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STUDENT 1: We would like
to present to you PV Next

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Gen, Earth-Abundant Materials.

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So the reason we're
doing this project

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is because there
are current limits

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to the high-quality
crystalline silicon

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cells that we're producing.

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There's too high of an
energy cost and too high

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of a carbon footprint.

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So we decided to identify
likely sources of failure

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for earth-abundant PV.

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We focus on tin sulfide, lead
sulfide, and cuprous oxide.

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So we took the approach
of subjecting these PV

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cells into a climate chamber
to sort of simulate aging,

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and accelerated aging, and the
effects of long-term operation

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out in the field.

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00:01:03,770 --> 00:01:05,406
So for a little bit
of a background,

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this is a graph that we'd
like to provide you with.

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If you notice, the graph
is centered around zero,

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which is crystalline silicon.

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00:01:12,360 --> 00:01:14,790
And on the x-axis,
it's kind of inverted.

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So the negative's on the right.

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00:01:16,340 --> 00:01:18,130
But this graph
sort of illustrates

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that where we want to
be, in our research,

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is in that quadrant
within the circle.

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Because that's where we have
the lowest materials extraction

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costs.

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And we have the highest
annual electricity potential.

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00:01:28,389 --> 00:01:29,930
So those are the
kind of technologies

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00:01:29,930 --> 00:01:32,090
that we want to be looking at.

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00:01:32,090 --> 00:01:34,810
And as you can see in the
arrowhead, cuprous oxide

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and lead sulfide are
in that quadrant.

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00:01:44,340 --> 00:01:45,910
JOEL: So we've
established, we've

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showed you how these kinds of
materials can be less expensive

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and, potentially, produce
more electricity than silicon.

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00:01:56,110 --> 00:01:58,670
However, they haven't
had the same kinds

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00:01:58,670 --> 00:02:02,370
of decades of experience
in testing as silicon has.

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00:02:02,370 --> 00:02:05,450
So we're trying to figure
out how they could possibly

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00:02:05,450 --> 00:02:09,479
fail under actual years
of operation in the field.

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00:02:09,479 --> 00:02:12,420
First, we're going to
talk about tin sulfide.

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Certainly, tin and
sulfur are both elements

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with which we're very familiar.

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Tin has a wide
manufacturing base.

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00:02:19,400 --> 00:02:24,720
Sulfur is part of all of our
biology, pretty easy to find.

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The band gap of this material
is 1.3 electronvolts,

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a little bit higher
than silicon.

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But that, actually,
brings it closer

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to the optimum of the
Shockley-Quiesser efficiency

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limits for a
single-junction solar cell.

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The maximum possible
efficiency is 32%.

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However, the current record
efficiency, for tin sulfide

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cells, is only 1.3%.

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So that gives you
an idea of the state

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of development of this field.

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Often, it seems that devices
are limited by their charge

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extraction.

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There is an interface
between the absorber layer

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and buffer layers that block
electron and hole transport.

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I'm going to talk about that a
little more on the next slide.

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But this interface has
been, unfortunately,

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not very well
characterized to date

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and is often a site of
high recombination rates

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that can limit the
current extracted.

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However, tin sulfide is a good
material for photovoltaics.

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Because it's crystal structure
is amenable to doping.

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You can add substituent
atoms and tune

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the electronic
properties that way.

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Also, it has a high
absorption coefficient.

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So it can be made into
thin film devices.

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And the device that we're
going to show you today

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was made using atomic
layer deposition.

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Here's that schematic
that I was mentioning.

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So as in this diagram, the light
is coming in from the bottom.

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Don't be alarmed.

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The bottom substrate, that
things are subsequently

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deposited onto, is
a glass pane that

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is coated with
fluorine-doped tin oxide.

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This is like indium tin oxide.

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It's another transparent
conducting material.

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And then, this layer here
is the tin sulfide absorber.

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And you can see that
on either side of it,

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there is a hole-blocking layer
and an electron-blocking layer,

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which prevents
charge from flowing

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in the opposite direction
that we want it to.

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And then, both the absorber
and the front contact

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have these metal stack
electrodes patterned onto them,

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00:04:36,830 --> 00:04:41,700
onto the same side of gold,
copper, and molybdenum.

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So this is a manufacturing idea
that could make tabbing easier

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00:04:47,350 --> 00:04:49,160
and eliminate shading losses.

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Because all of your electronics
contact to one side on the back

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00:04:53,850 --> 00:04:54,510
here.

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However, as we'll
discuss later, it

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00:04:56,877 --> 00:04:58,460
comes with some
challenges of its own.

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JOLENE: The other
material that we

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investigated, for this
project, was lead sulfide.

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Lead sulfide is also an
earth-abundant material.

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Lead is even more
abundant than tin.

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The bulk band gap
of lead sulfide

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is only 0.41 eV, which
is a little bit too

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00:05:18,260 --> 00:05:21,230
low to make it a good observer
material for photovoltaics.

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00:05:21,230 --> 00:05:25,741
But if you make nanocrystals,
you can tune the band gap.

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So there's confinement effects
that make it so that the band

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00:05:28,240 --> 00:05:30,360
gap can actually become larger.

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00:05:30,360 --> 00:05:32,630
So we looked at lead sulfide
quantum dot solar cells.

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00:05:32,630 --> 00:05:36,360
And in particular, we looked
at lead sulfide quantum dots

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00:05:36,360 --> 00:05:39,767
and a PCBM, which is a fullerene
derivative heterojunction,

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00:05:39,767 --> 00:05:41,600
where the lead sulfide
is a p-type material.

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00:05:41,600 --> 00:05:43,850
The PCBM is the n-type material.

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And we just made a
bilayer heterojunction.

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With these materials, the
major potential failure mode,

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that we identified,
was oxidation

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of both the lead sulfide
quantum dots and the fullerenes.

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00:05:54,460 --> 00:05:56,080
And then, there's
also possibilities

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00:05:56,080 --> 00:06:01,500
of hydrolysis of this
PCBM esther group

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00:06:01,500 --> 00:06:04,170
upon reaction with the
EVA encapsulant material.

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00:06:04,170 --> 00:06:06,870
That was something that we
thought might be a problem.

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00:06:06,870 --> 00:06:09,370
The current record efficiency
for these lead sulfide quantum

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00:06:09,370 --> 00:06:11,520
dot solar cells is only 2.1%.

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Also something, more
work needs to be done

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in improving that efficiency.

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00:06:16,420 --> 00:06:18,539
But a major advantage
of this material system

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is that both the lead sulfide
quantum dots and the fullerenes

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can be solution-processed.

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00:06:22,480 --> 00:06:24,900
So they can be spin cast
onto your substrate, which

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makes the processing
cost very low,

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especially compared to growing
a single crystalline wafer.

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The device architecture
that we used

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is, again, glass coated with
a transparent conducting oxide

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00:06:39,040 --> 00:06:40,580
electrode.

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And then, there's just a bilayer
heterojunction with the two

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00:06:43,630 --> 00:06:45,200
observing materials.

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00:06:45,200 --> 00:06:49,570
And then, finally, it's a metal
contact on the opposite side.

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00:06:49,570 --> 00:06:53,430
For our case, I've shown the
band structure of the devices

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00:06:53,430 --> 00:06:54,320
that we used.

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And, in particular,
I wanted to point out

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that the top
electrode, in our case,

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00:06:59,000 --> 00:07:02,200
was actually aluminum because
of the band alignment.

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00:07:02,200 --> 00:07:04,150
The work function
of aluminum makes it

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00:07:04,150 --> 00:07:06,820
so that the top band
aligns well with the PCBM.

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00:07:06,820 --> 00:07:08,650
And you can get charge
extraction the way

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00:07:08,650 --> 00:07:10,360
that you want.

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00:07:10,360 --> 00:07:12,450
And, again, our devices,
the quantum dots

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were tuned so that the
band gap was about 1 eV.

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And these are the parameters
for the devices that we used.

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STUDENT 4: All right, so what
we did is our initial plan

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was to collect IV curves of
before and after encapsulation

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00:07:32,740 --> 00:07:34,770
of our solar cells, and
after a period of time

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00:07:34,770 --> 00:07:36,710
spent in the
environmental chamber.

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00:07:36,710 --> 00:07:39,430
The encapsulation that we chose,
from a variety of materials,

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was EVA.

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Because it's an
industry standard.

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00:07:42,950 --> 00:07:46,410
For environmental chamber, we
kept it at 85 degrees Celsius

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00:07:46,410 --> 00:07:51,040
and at 85% relative humidity
to accelerate the degradation

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00:07:51,040 --> 00:07:52,610
process.

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00:07:52,610 --> 00:07:54,080
Then, we took
photos of our cells

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00:07:54,080 --> 00:07:56,570
over a period of seven days.

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00:07:56,570 --> 00:07:58,574
Here's a schematic of
an encapsulated cell.

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00:07:58,574 --> 00:08:00,615
It's a layer of glass
followed by a layer of EVA,

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00:08:00,615 --> 00:08:03,000
then the solar cell,
another layer of EVA,

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00:08:03,000 --> 00:08:07,960
and then a TPE backsheet--
again industry standard.

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00:08:07,960 --> 00:08:10,620
For our tin sulfide,
what we did is

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00:08:10,620 --> 00:08:13,000
we actually omitted the glass
layer in our encapsulation.

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00:08:13,000 --> 00:08:16,830
Because the cell came with
glass, was made with glass.

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00:08:16,830 --> 00:08:18,585
So to make the
contact, so we did

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00:08:18,585 --> 00:08:20,940
is we applied silver paste
to attach the tabbing.

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00:08:20,940 --> 00:08:24,140
And we baked them at 45 degrees
C to evaporate the solvent.

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00:08:24,140 --> 00:08:27,450
This yielded very
delicate contacts.

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00:08:27,450 --> 00:08:29,400
So we had to encapsulate
immediately in order

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00:08:29,400 --> 00:08:31,179
to hold the contacts in place.

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00:08:31,179 --> 00:08:32,720
Unfortunately, as
Joel was mentioning

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00:08:32,720 --> 00:08:35,130
about how the two
electrodes are on the back,

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00:08:35,130 --> 00:08:37,620
during the encapsulation
process, we shorted our cell.

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00:08:37,620 --> 00:08:39,590
So we were unable
to take an IV curve.

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00:08:42,390 --> 00:08:44,650
For the lead sulfide,
initially-- as

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00:08:44,650 --> 00:08:47,260
Jolene said-- we had
aluminum contacts.

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00:08:47,260 --> 00:08:48,810
Unfortunately, when
exposed to air,

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00:08:48,810 --> 00:08:51,280
this forms a layer of
aluminum oxide, which is

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00:08:51,280 --> 00:08:53,400
nearly impossible to solder to.

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00:08:53,400 --> 00:08:56,710
So we switched the
aluminum with silver,

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00:08:56,710 --> 00:09:01,390
even though it's less than
ideal for a charge extraction.

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00:09:01,390 --> 00:09:03,400
And with these
contacts, we were only

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00:09:03,400 --> 00:09:07,120
able to achieve a contact
with a large amount of solder.

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00:09:07,120 --> 00:09:08,900
And again, we could
not encapsulate.

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00:09:08,900 --> 00:09:13,560
Because we risk breaking the
cell with these contacts.

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00:09:13,560 --> 00:09:17,480
What we decided to do, then,
was encapsulate unsoldered cells

192
00:09:17,480 --> 00:09:20,700
with aluminum contacts, and
do a qualitative assessment

193
00:09:20,700 --> 00:09:22,690
of the color change,
which would indicate

194
00:09:22,690 --> 00:09:28,250
a reaction with the encapsulant
or with the water oxygen.

195
00:09:28,250 --> 00:09:30,800
So basically, unfortunately,
despite our initial plan,

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00:09:30,800 --> 00:09:33,482
we were unable to collect IV
curves for either type of cell

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00:09:33,482 --> 00:09:34,315
after encapsulation.

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00:09:47,480 --> 00:09:50,720
DANNY: So we did a series of
cross-sectional [INAUDIBLE]

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00:09:50,720 --> 00:09:55,530
images on tin sulfide device
before and after several days

200
00:09:55,530 --> 00:09:58,210
in the environmental chamber.

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00:09:58,210 --> 00:10:01,140
So on the left, you have an
image of the tin sulfide layer

202
00:10:01,140 --> 00:10:03,970
before exposure to the chamber.

203
00:10:03,970 --> 00:10:06,610
And we can see the columnar
structure of the tin sulfide

204
00:10:06,610 --> 00:10:08,060
layer.

205
00:10:08,060 --> 00:10:10,500
However, after several
days, on the right

206
00:10:10,500 --> 00:10:14,800
is an image of the tin sulfide
layer having some changes,

207
00:10:14,800 --> 00:10:17,430
having undergone some
changes to its structure.

208
00:10:17,430 --> 00:10:21,770
This may be due to either
thermal degradation or a result

209
00:10:21,770 --> 00:10:25,330
of [? cleavage ?] of the cell.

210
00:10:25,330 --> 00:10:30,040
We also did a series of photos
over the course of several days

211
00:10:30,040 --> 00:10:31,520
on the devices.

212
00:10:31,520 --> 00:10:34,270
And we noticed that there
was some color changes

213
00:10:34,270 --> 00:10:35,350
in the device.

214
00:10:35,350 --> 00:10:38,540
The tin sulfide
layer has undergone,

215
00:10:38,540 --> 00:10:42,050
the color of tin sulfide
layer darkened over time,

216
00:10:42,050 --> 00:10:44,593
especially near the
corners of the cell,

217
00:10:44,593 --> 00:10:49,830
like around this edge here.

218
00:10:49,830 --> 00:10:51,560
For the photo on
the extreme right,

219
00:10:51,560 --> 00:10:54,100
you may notice some
yellowish tinge.

220
00:10:54,100 --> 00:10:57,940
And that is due to the lighting
the photo was taken in and not

221
00:10:57,940 --> 00:11:01,016
an actual change in the cell.

222
00:11:01,016 --> 00:11:04,580
So as for lead sulfide, we
did a similar series of photos

223
00:11:04,580 --> 00:11:05,520
on the device.

224
00:11:05,520 --> 00:11:07,630
And you notice a
similar color change

225
00:11:07,630 --> 00:11:10,990
has occurred across the device.

226
00:11:10,990 --> 00:11:13,520
You also notice that
at the four corners,

227
00:11:13,520 --> 00:11:14,790
there are contacts there.

228
00:11:14,790 --> 00:11:19,720
And these contacts have been
tarnished significantly.

229
00:11:19,720 --> 00:11:22,770
So we think that the color
changes, on both devices,

230
00:11:22,770 --> 00:11:26,376
may be due to, one, the
leakage of the encapsulant,

231
00:11:26,376 --> 00:11:29,220
two, the reaction
with the encapsulant,

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00:11:29,220 --> 00:11:31,500
and lastly, due to
thermal degradation.

233
00:11:41,950 --> 00:11:43,860
KATHERINE: So if
we're going to achieve

234
00:11:43,860 --> 00:11:47,410
terawatt-scale electricity
output with solar energy,

235
00:11:47,410 --> 00:11:52,150
we need new materials that
are cheap and efficient.

236
00:11:52,150 --> 00:11:54,530
However, the materials
we investigated still

237
00:11:54,530 --> 00:11:57,370
have a lot of work to be done
before they can achieve that.

238
00:11:57,370 --> 00:12:01,460
In particular, they have
very low efficiencies.

239
00:12:01,460 --> 00:12:03,470
And that's something
that absolutely

240
00:12:03,470 --> 00:12:05,260
needs to be overcome.

241
00:12:05,260 --> 00:12:08,410
However, we focused more on
some of the other issues,

242
00:12:08,410 --> 00:12:09,700
such as the contacts.

243
00:12:09,700 --> 00:12:11,870
Right now, they're still
in the research phase.

244
00:12:11,870 --> 00:12:15,550
So, for example, using
aluminum as a contact is fine.

245
00:12:15,550 --> 00:12:18,850
However, when moving
into commercialization,

246
00:12:18,850 --> 00:12:20,322
aluminum contacts
will have to be

247
00:12:20,322 --> 00:12:21,530
replaced with something else.

248
00:12:21,530 --> 00:12:24,297
Or something else will
have to be deposited

249
00:12:24,297 --> 00:12:25,255
on top of the aluminum.

250
00:12:28,640 --> 00:12:32,480
We saw degradation of the
encapsulated cells, which

251
00:12:32,480 --> 00:12:35,350
indicates that the current
encapsulant will not

252
00:12:35,350 --> 00:12:36,685
work with these new materials.

253
00:12:39,720 --> 00:12:44,030
In particular, we think that we
need an encapsulant that will,

254
00:12:44,030 --> 00:12:46,170
does not have an acidic
degradation product.

255
00:12:46,170 --> 00:12:51,780
Because that was a serious
issue with the PbS quantum dot

256
00:12:51,780 --> 00:12:57,450
solar cells, with
the fullerene part

257
00:12:57,450 --> 00:13:00,350
can react with acid and degrade.

258
00:13:00,350 --> 00:13:05,190
So we think, we did talk
about wanting class Evb?

259
00:13:05,190 --> 00:13:05,940
JOEL: PVB.

260
00:13:05,940 --> 00:13:07,480
KATHERINE: PVB.

261
00:13:07,480 --> 00:13:11,130
But we did not have
access to that material.

262
00:13:11,130 --> 00:13:13,770
And we think that the
method that we came up

263
00:13:13,770 --> 00:13:16,890
with of testing materials
in the environmental chamber

264
00:13:16,890 --> 00:13:18,290
will be useful in the future.

265
00:13:18,290 --> 00:13:20,725
And ideally, you could
test different encapsulants

266
00:13:20,725 --> 00:13:24,830
and see how well
the IV curves stay

267
00:13:24,830 --> 00:13:27,380
after the environmental testing.

268
00:13:27,380 --> 00:13:29,460
So we'd like to
thank several people

269
00:13:29,460 --> 00:13:32,710
for helping with our
project, in particular Andy

270
00:13:32,710 --> 00:13:36,680
at Fraunhofer, who's
actually here today.

271
00:13:36,680 --> 00:13:40,330
We had to go to
Fraunhofer several times

272
00:13:40,330 --> 00:13:43,570
to-- we had several iterations
of getting the cells.

273
00:13:43,570 --> 00:13:46,230
And then, once we put
them in the chamber,

274
00:13:46,230 --> 00:13:47,810
we had to take
pictures every day.

275
00:13:47,810 --> 00:13:51,440
So he was there and was
able to help us with that.

276
00:13:51,440 --> 00:13:53,560
Also we'd like to thank
Darcy of the Bawendi Group

277
00:13:53,560 --> 00:13:57,550
for making the PbS
quantum dot cells for us.

278
00:13:57,550 --> 00:14:01,740
And also the Gordon Group for
making the tin sulfide cells.

279
00:14:01,740 --> 00:14:04,350
And then, finally Professor
Buonassisi and Joe

280
00:14:04,350 --> 00:14:09,880
for teaching us all the
fundamentals of the devices.

281
00:14:09,880 --> 00:14:12,090
So before we go
to questions, we'd

282
00:14:12,090 --> 00:14:16,190
like to pass around
the cells we had.

283
00:14:16,190 --> 00:14:18,000
While people are
asking questions,

284
00:14:18,000 --> 00:14:23,240
we ask that you don't take them
out of the bag or the boxes

285
00:14:23,240 --> 00:14:27,080
just because some them contain
lead, which it can be harmful.

286
00:14:27,080 --> 00:14:31,319
But we can pass this around
while we open for questions.

287
00:14:31,319 --> 00:14:32,485
PROFESSOR: Thank you, group,

288
00:14:32,485 --> 00:14:34,465
[APPLAUSE]

289
00:14:46,345 --> 00:14:47,335
JOEL: David.

290
00:14:47,335 --> 00:14:50,305
AUDIENCE: So why, does
FTO have a different work

291
00:14:50,305 --> 00:14:51,295
function from ITO?

292
00:14:51,295 --> 00:14:55,250
Or for what was the reason that
you used FTO in the consultant

293
00:14:55,250 --> 00:14:55,750
itself?

294
00:14:55,750 --> 00:14:59,730
JOEL: I'd like to direct
that question to Danny.

295
00:14:59,730 --> 00:15:02,420
DANNY: FTO is typically much
cheaper compared to ITO.

296
00:15:02,420 --> 00:15:05,010
So for research
purposes, we prefer FTO.

297
00:15:09,110 --> 00:15:12,479
JOEL: Is it, light leaves
out the indium, right?

298
00:15:12,479 --> 00:15:13,020
DANNY: Right.

299
00:15:13,020 --> 00:15:14,497
So indium's a rare matel.

300
00:15:14,497 --> 00:15:16,580
And it's very expensive
and the price is going up.

301
00:15:16,580 --> 00:15:19,820
So we try not to use
indium in our TCO.

302
00:15:19,820 --> 00:15:22,630
AUDIENCE: Is it the
same conductivity?

303
00:15:22,630 --> 00:15:23,130
DANNY: No.

304
00:15:23,130 --> 00:15:24,840
For ITO, the conductivity
is much better

305
00:15:24,840 --> 00:15:26,980
but, yeah, much better than FTO.

306
00:15:29,790 --> 00:15:34,210
JOEL: Still working on
the transparent oxide

307
00:15:34,210 --> 00:15:36,628
side of earth-abundancy.

308
00:15:36,628 --> 00:15:39,399
Different project,
though, I guess.

309
00:15:39,399 --> 00:15:41,857
AUDIENCE: Can you guys go back
to the environmental chamber

310
00:15:41,857 --> 00:15:44,098
pictures for, I
think, tin sulfide?

311
00:15:47,086 --> 00:15:48,090
Yeah.

312
00:15:48,090 --> 00:15:51,200
So, yeah, can you just
walk me through this again?

313
00:15:51,200 --> 00:15:54,030
The yellow is not what my
eye should be drawn to?

314
00:15:54,030 --> 00:15:57,120
JOEL: Yeah, that's a
really unfortunate side

315
00:15:57,120 --> 00:16:05,000
effect of the way that
the camera was that day.

316
00:16:05,000 --> 00:16:07,620
But it's, I think,
it would show up

317
00:16:07,620 --> 00:16:09,990
better if we turn
down the room lights.

318
00:16:09,990 --> 00:16:15,780
But there is a darkening
from Day 2 to Day 3,

319
00:16:15,780 --> 00:16:16,950
and then, also, to Day 6.

320
00:16:16,950 --> 00:16:20,690
But that's kind of overwhelmed
by the yellow glare.

321
00:16:20,690 --> 00:16:23,190
Yeah, maybe now you can
see it a little bit better.

322
00:16:23,190 --> 00:16:28,330
And we also wanted to point
out that although this happens

323
00:16:28,330 --> 00:16:32,060
across the whole device,
there's particularly

324
00:16:32,060 --> 00:16:35,230
more change around the edges.

325
00:16:35,230 --> 00:16:38,660
So that to us says
that there's definitely

326
00:16:38,660 --> 00:16:42,490
something happening here where
the atmosphere is leaking in

327
00:16:42,490 --> 00:16:46,760
through the encapsulant and
reacting with the device.

328
00:16:46,760 --> 00:16:48,890
Because that will
happen from the outside

329
00:16:48,890 --> 00:16:52,460
in, as opposed to a reaction
with the encapsulant

330
00:16:52,460 --> 00:16:55,070
itself or a thermal
process, which

331
00:16:55,070 --> 00:16:57,495
would affect the whole
device uniformly.

332
00:16:57,495 --> 00:16:59,670
AUDIENCE: And this was EVA?

333
00:16:59,670 --> 00:17:00,490
JOEL: Yes.

334
00:17:00,490 --> 00:17:02,934
AUDIENCE: So, I mean, EVA's
a pretty standard encapsulant

335
00:17:02,934 --> 00:17:03,434
material.

336
00:17:03,434 --> 00:17:03,851
JOEL: Yep.

337
00:17:03,851 --> 00:17:06,040
AUDIENCE: Do you think that
there is something like the EVA

338
00:17:06,040 --> 00:17:07,079
process that you used?

339
00:17:07,079 --> 00:17:09,287
Or do you think there's some
reaction between the tin

340
00:17:09,287 --> 00:17:14,188
sulfide and the EVA that
caused these EVA films to not

341
00:17:14,188 --> 00:17:15,650
be good encapsulants?

342
00:17:15,650 --> 00:17:19,609
JOLENE: So this one,
the process that we

343
00:17:19,609 --> 00:17:23,440
used to encapsulate these
were not at Fraunhofer.

344
00:17:23,440 --> 00:17:26,290
These were encapsulated
in Joel's lab.

345
00:17:26,290 --> 00:17:29,365
And so I think that,
and the devices,

346
00:17:29,365 --> 00:17:31,490
both devices that we worked
with were kind of hard.

347
00:17:31,490 --> 00:17:33,830
They aren't meant
to be encapsulated.

348
00:17:33,830 --> 00:17:36,000
So I think that
part of the problem

349
00:17:36,000 --> 00:17:38,270
is just the geometry of
the device and the presses

350
00:17:38,270 --> 00:17:39,436
that we used and everything.

351
00:17:39,436 --> 00:17:41,290
We probably just didn't
get a very good seal

352
00:17:41,290 --> 00:17:43,190
around the outside.

353
00:17:43,190 --> 00:17:45,410
And so in this
case in particular,

354
00:17:45,410 --> 00:17:48,410
I think that it's
more likely that it's

355
00:17:48,410 --> 00:17:49,900
just not a very good seal.

356
00:17:49,900 --> 00:17:52,560
So we're getting some leakage
rather than the tin sulfide

357
00:17:52,560 --> 00:17:53,970
is reacting with the EVA.

358
00:17:53,970 --> 00:17:56,160
For the quantum dots, it's
a little bit less clear

359
00:17:56,160 --> 00:17:59,580
if there's a reaction
with the EVA or not.

360
00:17:59,580 --> 00:18:01,690
Because there's a
little bit, there's

361
00:18:01,690 --> 00:18:04,970
both degradation
from, or color changes

362
00:18:04,970 --> 00:18:08,020
from the outside that affect
particularly the outside.

363
00:18:08,020 --> 00:18:11,820
And there's, also, color changes
that affect the whole device.

364
00:18:11,820 --> 00:18:14,620
And so, then, it's either
the quantum dots are somehow

365
00:18:14,620 --> 00:18:17,505
changing or there may
be some kind of reaction

366
00:18:17,505 --> 00:18:18,380
with the encapsulant.

367
00:18:18,380 --> 00:18:22,874
But when we took the SEM
images, the EDX aspect of it

368
00:18:22,874 --> 00:18:23,540
was not working.

369
00:18:23,540 --> 00:18:29,640
So it was difficult to do any
kind of elemental analysis

370
00:18:29,640 --> 00:18:30,240
there.

371
00:18:30,240 --> 00:18:32,450
AUDIENCE: And just
one other question,

372
00:18:32,450 --> 00:18:36,630
in this sort of accelerated
aging process, how long

373
00:18:36,630 --> 00:18:39,100
would you want to see
stability for a, say,

374
00:18:39,100 --> 00:18:40,820
a 30-year or 20-year?

375
00:18:40,820 --> 00:18:43,304
If you were going to
warranty this cell for me,

376
00:18:43,304 --> 00:18:44,513
how long would you might say?

377
00:18:44,513 --> 00:18:46,845
KATHERINE: I think, usually,
they do at least six weeks.

378
00:18:46,845 --> 00:18:47,724
AUDIENCE: Six weeks?

379
00:18:47,724 --> 00:18:48,224
JOEL: Yeah.

380
00:18:48,224 --> 00:18:48,716
JOLENE: Yeah.

381
00:18:48,716 --> 00:18:50,924
KATHERINE: And so this was,
we didn't have six weeks.

382
00:18:50,924 --> 00:18:53,144
But we still
[INAUDIBLE] that said.

383
00:18:53,144 --> 00:18:53,980
So.

384
00:18:53,980 --> 00:18:55,900
JOLENE: More work
should be done.

385
00:18:55,900 --> 00:18:58,340
AUDIENCE: So how long's
your warranty on the cell?

386
00:18:58,340 --> 00:18:59,280
JOLENE: Like a day.

387
00:18:59,280 --> 00:19:01,160
[LAUGHTER]

388
00:19:04,650 --> 00:19:06,600
JOEL: There were
other encapsulants

389
00:19:06,600 --> 00:19:09,910
available at Fraunhofer.

390
00:19:09,910 --> 00:19:13,110
Notably, there's
this, a thermoplastic

391
00:19:13,110 --> 00:19:14,770
and an ionomer encapsulant.

392
00:19:14,770 --> 00:19:19,490
But these are both new and have
entirely proprietary chemical

393
00:19:19,490 --> 00:19:20,590
composition.

394
00:19:20,590 --> 00:19:23,620
So we didn't think it would
be very informative to study

395
00:19:23,620 --> 00:19:24,390
for our project.

396
00:19:24,390 --> 00:19:26,700
Because if we saw
something happen,

397
00:19:26,700 --> 00:19:29,860
we wouldn't really be
able to hypothesize

398
00:19:29,860 --> 00:19:32,000
where that came from.

399
00:19:32,000 --> 00:19:33,850
But there are other
materials out there

400
00:19:33,850 --> 00:19:37,740
besides the standard EVA and
the polyvinyl butyrate, the PVB

401
00:19:37,740 --> 00:19:40,490
that Katherine
mentioned at the end.

402
00:19:40,490 --> 00:19:43,100
Just not quite as far along.

403
00:19:46,972 --> 00:19:47,940
Yeah.

404
00:19:47,940 --> 00:19:50,844
AUDIENCE: So how would you
compare the degradation

405
00:19:50,844 --> 00:19:53,270
between ITO and FTO like--

406
00:19:53,270 --> 00:19:55,140
JOEL: The degradation
of ITO and FTO?

407
00:19:55,140 --> 00:19:56,759
AUDIENCE: How would
you compare this?

408
00:19:56,759 --> 00:19:58,300
Which one would you
pick [INAUDIBLE]?

409
00:19:58,300 --> 00:20:01,800
I mean, in terms of
cost, OK. [INAUDIBLE].

410
00:20:01,800 --> 00:20:04,702
In terms of technique,
it would be--

411
00:20:04,702 --> 00:20:06,410
AUDIENCE: So can you
repeat the question?

412
00:20:06,410 --> 00:20:10,080
JOEL: The question is if there's
a difference in the degradation

413
00:20:10,080 --> 00:20:13,040
between ITO, the
indium tin oxide,

414
00:20:13,040 --> 00:20:16,660
and FTO, the fluorine
doped tin oxide that we

415
00:20:16,660 --> 00:20:22,010
used in our tin sulfide cells.

416
00:20:22,010 --> 00:20:23,120
Yeah.

417
00:20:23,120 --> 00:20:24,745
Do you know anything
about that, Danny?

418
00:20:24,745 --> 00:20:28,840
DANNY: Yeah, so they normally
degrade when you expose them

419
00:20:28,840 --> 00:20:32,275
to extended temperatures above
650 degrees Celsius, which

420
00:20:32,275 --> 00:20:34,740
is unlikely to happen in
a normal day situation.

421
00:20:34,740 --> 00:20:37,730
So there's no difference
in this [INAUDIBLE].

422
00:20:37,730 --> 00:20:41,410
Yeah, we didn't expose
them to 650 Celsius

423
00:20:41,410 --> 00:20:43,534
in our accelerated
testing either.

424
00:20:47,166 --> 00:20:49,690
AUDIENCE: I have a question
about the aluminum contacts.

425
00:20:49,690 --> 00:20:51,442
First of all, how
did you deposit them?

426
00:20:55,140 --> 00:20:59,800
JOLENE: The aluminum
contacts were thermally

427
00:20:59,800 --> 00:21:02,731
evaporated onto the, yeah.

428
00:21:02,731 --> 00:21:04,699
AUDIENCE: So would
it be possible just

429
00:21:04,699 --> 00:21:06,106
to evaporate the [INAUDIBLE].

430
00:21:09,109 --> 00:21:10,650
JOLENE: Yeah,
absolutely, absolutely.

431
00:21:10,650 --> 00:21:13,024
We were working with cells
that had previously been made.

432
00:21:13,024 --> 00:21:16,100
That this was not our group,
we were getting materials from,

433
00:21:16,100 --> 00:21:18,556
generous donations
from another group.

434
00:21:18,556 --> 00:21:20,680
And so there were cells
that had already been made,

435
00:21:20,680 --> 00:21:22,263
already had aluminum
contacts on them.

436
00:21:22,263 --> 00:21:24,999
And so then, it would've
been much more involved

437
00:21:24,999 --> 00:21:27,290
to get other people in other
groups to do stuff for us.

438
00:21:27,290 --> 00:21:29,095
So we just used the
materials that we had.

439
00:21:29,095 --> 00:21:31,580
AUDIENCE: And I'm guessing
they don't see these problems

440
00:21:31,580 --> 00:21:34,489
because they don't solder their
contacts, just scrub them?

441
00:21:34,489 --> 00:21:36,120
JOLENE: Yeah.

442
00:21:36,120 --> 00:21:38,130
All the tests for the
lead sulfide cells

443
00:21:38,130 --> 00:21:40,080
are done in a glovebox,
an inner atmosphere.

444
00:21:40,080 --> 00:21:42,210
And they have pins
that just come down.

445
00:21:42,210 --> 00:21:44,053
AUDIENCE: Right, so
it just [INAUDIBLE].

446
00:21:44,053 --> 00:21:46,018
JOLENE: Yeah.

447
00:21:46,018 --> 00:21:46,518
Mm-hm?

448
00:21:46,518 --> 00:21:47,268
PROFESSOR: Ashley.

449
00:21:47,268 --> 00:21:49,810
AUDIENCE: I'm just curious,
more of a logistical question,

450
00:21:49,810 --> 00:21:53,155
did you guys have a camera
in the environmental chamber?

451
00:21:53,155 --> 00:21:55,151
Or do you have to take
them out each day?

452
00:21:55,151 --> 00:21:57,646
KATHERINE: And so we would
have to turn off the chamber,

453
00:21:57,646 --> 00:22:01,139
cool it down, take the
cell out, take a picture,

454
00:22:01,139 --> 00:22:03,135
put the cell back in,
then turn it back on.

455
00:22:03,135 --> 00:22:05,140
AUDIENCE: OK.

456
00:22:05,140 --> 00:22:08,366
JOEL: So in a sense, we actually
put extra stress on them.

457
00:22:08,366 --> 00:22:12,179
Because there was thermal
cycling [INAUDIBLE].

458
00:22:12,179 --> 00:22:14,262
AUDIENCE: So maybe a two-day
warranty [INAUDIBLE].

459
00:22:14,262 --> 00:22:14,970
KATHERINE: Mm-hm.

460
00:22:17,571 --> 00:22:19,696
AUDIENCE: Did you try
leaving the cells [INAUDIBLE]

461
00:22:19,696 --> 00:22:24,636
in the glovebox
after you [INAUDIBLE]

462
00:22:24,636 --> 00:22:28,872
go down and, then,
try to [INAUDIBLE]?

463
00:22:28,872 --> 00:22:31,080
AUDIENCE: Can he just repeat
the question again, too?

464
00:22:31,080 --> 00:22:31,760
Sorry.

465
00:22:31,760 --> 00:22:34,600
KATHERINE: Yeah, so he was
asking about the contacting,

466
00:22:34,600 --> 00:22:37,440
the PVS devices.

467
00:22:37,440 --> 00:22:42,260
And we did have, we
had two things we did.

468
00:22:42,260 --> 00:22:45,390
One was we took
them in the glovebox

469
00:22:45,390 --> 00:22:48,320
and tried to scratch off
the aluminum oxide layer,

470
00:22:48,320 --> 00:22:51,520
and then put silver
paste on, and then make

471
00:22:51,520 --> 00:22:53,190
the contacts to that.

472
00:22:53,190 --> 00:22:54,690
And that still didn't work.

473
00:22:54,690 --> 00:22:57,685
And then, we also got new
devices with silver contacts

474
00:22:57,685 --> 00:22:58,997
on them.

475
00:22:58,997 --> 00:23:00,080
And that also didn't work.

476
00:23:00,080 --> 00:23:01,936
Because it either would
stick to the device,

477
00:23:01,936 --> 00:23:03,310
or it would stick
to the contact.

478
00:23:03,310 --> 00:23:05,112
But it wouldn't stick
to both at once.

479
00:23:05,112 --> 00:23:06,320
And they would just peel off.

480
00:23:10,689 --> 00:23:12,230
JOLENE: The contacts
on those devices

481
00:23:12,230 --> 00:23:16,670
are less than 50
nanometers thick.

482
00:23:16,670 --> 00:23:20,100
So it, in general,
soldering to them

483
00:23:20,100 --> 00:23:22,414
was going to be challenging.

484
00:23:22,414 --> 00:23:23,455
STUDENT 1: We tried hard.

485
00:23:23,455 --> 00:23:24,887
[LAUGHTER]

486
00:23:25,387 --> 00:23:27,330
JOLENE: Yep.

487
00:23:27,330 --> 00:23:28,890
AUDIENCE: Is there
any future plans

488
00:23:28,890 --> 00:23:31,556
to continue with this work, with
either Bawendi or Gordon Group?

489
00:23:31,556 --> 00:23:34,085
Or are they, was just
kind of included?

490
00:23:34,085 --> 00:23:35,960
JOLENE: Well, I think
both of these materials

491
00:23:35,960 --> 00:23:39,210
are so much still in the
trying to boost efficiency

492
00:23:39,210 --> 00:23:45,912
phase that it is less important
to be able to say, to talk

493
00:23:45,912 --> 00:23:48,370
about the long-term stability
than to say that they're even

494
00:23:48,370 --> 00:23:52,080
viable materials to begin with.

495
00:23:52,080 --> 00:23:54,080
I think that they are
interested in the results.

496
00:23:54,080 --> 00:23:56,342
But, yeah.

497
00:23:56,342 --> 00:23:58,246
JOEL: I mean, this is
Danny's thesis, so.

498
00:23:58,246 --> 00:23:59,174
[LAUGHTER]

499
00:23:59,674 --> 00:24:03,320
DANNY: All right, so
[INAUDIBLE] from Gordon's Group,

500
00:24:03,320 --> 00:24:06,300
we have much more problems
much greater than whether they

501
00:24:06,300 --> 00:24:08,299
can last a week or two.

502
00:24:08,299 --> 00:24:09,796
[LAUGHTER]

503
00:24:10,833 --> 00:24:12,291
PROFESSOR: One more
question, guys.

504
00:24:12,291 --> 00:24:13,788
Yes.

505
00:24:13,788 --> 00:24:20,562
AUDIENCE: Do you IV curves
for Day 1 and Day 8?

506
00:24:20,562 --> 00:24:22,770
KATHERINE: Yeah, so we
weren't able to get IV curves.

507
00:24:22,770 --> 00:24:25,389
Because the tin
sulfide self-shorted,

508
00:24:25,389 --> 00:24:28,258
and we weren't able to make
contacts to the lead sulfide,

509
00:24:28,258 --> 00:24:28,758
so.

510
00:24:28,758 --> 00:24:30,216
AUDIENCE: Make
enough as to make up

511
00:24:30,216 --> 00:24:36,243
for what would be the
drop in-- [INAUDIBLE].

512
00:24:36,243 --> 00:24:40,235
KATHERINE: So Danny has
taken tin sulfide IV

513
00:24:40,235 --> 00:24:42,559
curves before the
encapsulation, right?

514
00:24:42,559 --> 00:24:43,100
DANNY: Right.

515
00:24:43,100 --> 00:24:44,730
So I [INAUDIBLE]
encapsulation and they

516
00:24:44,730 --> 00:24:47,610
do what you see here,
pretty decent IV curve.

517
00:24:47,610 --> 00:24:50,210
But before we did
the encapsulation,

518
00:24:50,210 --> 00:24:52,300
the cell shorted and
[INAUDIBLE] died.

519
00:24:52,300 --> 00:24:55,010
So we couldn't-- there's no
point in doing IV curve after

520
00:24:55,010 --> 00:24:55,590
the test.

521
00:24:57,805 --> 00:24:58,930
KATHERINE: So we took them.

522
00:24:58,930 --> 00:25:02,381
But it's just a straight line.

523
00:25:02,381 --> 00:25:04,425
AUDIENCE: [INAUDIBLE]

524
00:25:04,425 --> 00:25:05,675
JOEL: All right, Thanks, guys.

525
00:25:05,675 --> 00:25:06,966
Let's thank our speakers again.

526
00:25:06,966 --> 00:25:08,490
[APPLAUSE]

527
00:25:10,480 --> 00:25:13,124
JACKSON: All right, this is
Ron, Rachel, Ben, Kirsten.

528
00:25:13,124 --> 00:25:13,790
And I'm Jackson.

529
00:25:13,790 --> 00:25:16,800
I'm going to introduce the
Lighting Africa project.

530
00:25:16,800 --> 00:25:19,490
So the main problem behind
our project is the following.

531
00:25:19,490 --> 00:25:22,990
There's about 580 million people
living off-the-grid in Africa,

532
00:25:22,990 --> 00:25:24,930
and about 10 million
small businesses

533
00:25:24,930 --> 00:25:27,200
operating off-grid in Africa.

534
00:25:27,200 --> 00:25:29,300
And as you can imagine,
after dark, they

535
00:25:29,300 --> 00:25:30,790
have a major lighting problem.

536
00:25:30,790 --> 00:25:35,130
So kids need lighting for
education, for reading,

537
00:25:35,130 --> 00:25:36,360
for studying, et cetera.

538
00:25:36,360 --> 00:25:38,942
And then, families need it
to interact with one another.

539
00:25:38,942 --> 00:25:40,400
And small businesses,
a lot of them

540
00:25:40,400 --> 00:25:42,960
would like to continue
operating after dark.

541
00:25:42,960 --> 00:25:45,380
And currently, what they
do is they use kerosene.

542
00:25:45,380 --> 00:25:47,430
But there's many problems
with kerosene lamps.

543
00:25:47,430 --> 00:25:50,320
So the first of which is that
it's a major health issue.

544
00:25:50,320 --> 00:25:54,130
So burning kerosene is about,
and like, for one night,

545
00:25:54,130 --> 00:25:56,360
is about smoking two
packs of cigarettes

546
00:25:56,360 --> 00:25:57,830
in terms of health issues.

547
00:25:57,830 --> 00:26:00,520
In addition, it's very
expensive for these families.

548
00:26:00,520 --> 00:26:01,850
They can barely afford to eat.

549
00:26:01,850 --> 00:26:03,810
And so buying a weekly
supply of kerosene

550
00:26:03,810 --> 00:26:05,930
is extremely hard for them.

551
00:26:05,930 --> 00:26:08,380
And furthermore, actually the
widespread use of kerosene,

552
00:26:08,380 --> 00:26:12,380
although low per capita, is
causing a large increase in CO2

553
00:26:12,380 --> 00:26:14,050
in the atmosphere.

554
00:26:14,050 --> 00:26:16,571
So this brings up a
large opportunity for us.

555
00:26:16,571 --> 00:26:18,320
And the World Bank
Lighting Africa project

556
00:26:18,320 --> 00:26:20,500
has proposed the
following solution.

557
00:26:20,500 --> 00:26:23,190
And that's solar portable
lanterns, or SPLs.

558
00:26:23,190 --> 00:26:25,480
And these are small
devices, maybe this big,

559
00:26:25,480 --> 00:26:28,460
that have a compact
fluorescent or an LED on them.

560
00:26:28,460 --> 00:26:29,890
And they have solar
panels on top.

561
00:26:29,890 --> 00:26:31,960
And you set the whole
device out during the day.

562
00:26:31,960 --> 00:26:33,640
And you can bring it
in during the night

563
00:26:33,640 --> 00:26:35,970
and use it to light your homes.

564
00:26:35,970 --> 00:26:38,610
And these are, right now, of
a fairly small market share,

565
00:26:38,610 --> 00:26:41,600
compared to the kerosene, but
are growing very substantially

566
00:26:41,600 --> 00:26:44,104
with a 40% to 50%
projected annual growth.

567
00:26:44,104 --> 00:26:45,520
And as you can see
from the graph,

568
00:26:45,520 --> 00:26:47,190
I'm sure you guys
are aware Africa

569
00:26:47,190 --> 00:26:50,640
has a huge solar resource
as a great opportunity.

570
00:26:50,640 --> 00:26:53,330
So the goals for our specific
project are the following.

571
00:26:53,330 --> 00:26:55,360
How will next generation
solar technologies

572
00:26:55,360 --> 00:26:58,490
help bring solar PV lights
to rural sub-Saharan Africa?

573
00:26:58,490 --> 00:27:00,720
So our specific project
is the following.

574
00:27:00,720 --> 00:27:04,480
How we looked at the next
generation of solar, so

575
00:27:04,480 --> 00:27:08,200
future technologies that are
emerging in the next six months

576
00:27:08,200 --> 00:27:10,620
to 10 years, and how they're
going to specifically affect

577
00:27:10,620 --> 00:27:11,187
our project.

578
00:27:11,187 --> 00:27:13,520
So to do this, we looked at
a few different time frames.

579
00:27:13,520 --> 00:27:16,524
We looked at the six to 12 month
time frame, the one to five

580
00:27:16,524 --> 00:27:18,690
year time frame, and the
five to 10 year time frame,

581
00:27:18,690 --> 00:27:21,479
and made technological
prospectus of each one,

582
00:27:21,479 --> 00:27:23,520
looked at a wide gamut of
different technologies,

583
00:27:23,520 --> 00:27:25,690
and selected a few that
we thought would most

584
00:27:25,690 --> 00:27:27,230
positively affect our project.

585
00:27:27,230 --> 00:27:29,880
And we focus on the one
to five year time frame.

586
00:27:29,880 --> 00:27:32,510
Because we thought that this
would be the most important to

587
00:27:32,510 --> 00:27:33,500
look at.

588
00:27:33,500 --> 00:27:36,000
So to do this, we looked at
a few, a couple different

589
00:27:36,000 --> 00:27:36,500
consumers.

590
00:27:36,500 --> 00:27:38,920
So the first consumer
is a low cost consumer.

591
00:27:38,920 --> 00:27:42,110
And this is somebody who can
barely afford to eat every day

592
00:27:42,110 --> 00:27:46,270
and, really, buys kerosene,
maybe, on a week-to-week basis.

593
00:27:46,270 --> 00:27:47,910
It's extremely
expensive for them.

594
00:27:47,910 --> 00:27:49,951
So we need to minimize
the costs of these devices

595
00:27:49,951 --> 00:27:54,060
as much as possible so that
they have a low buyback time

596
00:27:54,060 --> 00:27:55,860
with compared to kerosene.

597
00:27:55,860 --> 00:27:57,560
And these devices
are often integrated.

598
00:27:57,560 --> 00:27:59,040
So there's a solar
panel on the device.

599
00:27:59,040 --> 00:28:00,570
And you put the whole
device out during the day.

600
00:28:00,570 --> 00:28:02,510
And you bring the whole
device in at night.

601
00:28:02,510 --> 00:28:06,469
The second consumer we looked at
is a higher performance device.

602
00:28:06,469 --> 00:28:08,010
And so this is a
consumer who, maybe,

603
00:28:08,010 --> 00:28:10,176
has a little bit more money
although still very poor

604
00:28:10,176 --> 00:28:12,380
relative to our standards.

605
00:28:12,380 --> 00:28:14,320
And then, often these
devices are separated.

606
00:28:14,320 --> 00:28:15,470
So you'll have a
separate solar panel

607
00:28:15,470 --> 00:28:16,870
that goes out during the day.

608
00:28:16,870 --> 00:28:19,370
And then, you'll bring either
the solar panel in or leave it

609
00:28:19,370 --> 00:28:19,650
outside.

610
00:28:19,650 --> 00:28:21,500
And maybe there's a
cable that connects it.

611
00:28:21,500 --> 00:28:23,626
And sometimes, these
are even on the roof.

612
00:28:23,626 --> 00:28:26,000
And these have a little bit
some added features that I'll

613
00:28:26,000 --> 00:28:28,435
talk about in a little bit.

614
00:28:28,435 --> 00:28:30,810
So to look at this, we looked
at a few different metrics.

615
00:28:30,810 --> 00:28:32,190
So the first,
obviously, is cost.

616
00:28:32,190 --> 00:28:33,610
And that's the most
important metric.

617
00:28:33,610 --> 00:28:36,276
So we looked at dollars per watt
of all these different devices,

618
00:28:36,276 --> 00:28:38,470
projected dollars per watt.

619
00:28:38,470 --> 00:28:40,334
And like I said
before, minimizing cost

620
00:28:40,334 --> 00:28:41,500
is the most important thing.

621
00:28:41,500 --> 00:28:44,830
Because these people
need an attractive device

622
00:28:44,830 --> 00:28:48,120
that will pay itself back fairly
quickly in terms of kerosene,

623
00:28:48,120 --> 00:28:50,907
and will be affordable.

624
00:28:50,907 --> 00:28:53,490
The second thing we looked at
is a performance, so efficiency,

625
00:28:53,490 --> 00:28:54,250
basically.

626
00:28:54,250 --> 00:28:57,080
So we looked at the parameter
watts per centimeter squared.

627
00:28:57,080 --> 00:28:58,570
And so we need to
minimize the size

628
00:28:58,570 --> 00:29:00,760
so that it can fit on a
device if it's integrated,

629
00:29:00,760 --> 00:29:03,080
or minimize the size
of a solar panel

630
00:29:03,080 --> 00:29:05,850
if you're going to lug
it in and out every day.

631
00:29:05,850 --> 00:29:08,700
And as performance goes up, you
can get a few added features.

632
00:29:08,700 --> 00:29:09,810
So one of the,
actually, big problems

633
00:29:09,810 --> 00:29:11,351
that, maybe, is
surprising is there's

634
00:29:11,351 --> 00:29:14,630
about 50 million off-grid mobile
phones at the current time.

635
00:29:14,630 --> 00:29:16,751
So these people live off-grid.

636
00:29:16,751 --> 00:29:18,750
They need a place to
charge their mobile phones.

637
00:29:18,750 --> 00:29:20,360
And often, they have to
bring in to the city center,

638
00:29:20,360 --> 00:29:21,940
or they use hand
cranks or something

639
00:29:21,940 --> 00:29:23,190
to charge their mobile phones.

640
00:29:23,190 --> 00:29:26,040
And it's expensive and
difficult for them to charge.

641
00:29:26,040 --> 00:29:28,490
So adding a charging
feature, to these devices,

642
00:29:28,490 --> 00:29:30,590
can be extremely helpful
and save a lot of money.

643
00:29:30,590 --> 00:29:32,790
In addition is you get
higher performance devices.

644
00:29:32,790 --> 00:29:35,800
You can start adding radios,
fans, and TV to improve

645
00:29:35,800 --> 00:29:36,717
their quality of life.

646
00:29:36,717 --> 00:29:38,549
So now, I'm going to
pass it off to Kirsten.

647
00:29:38,549 --> 00:29:41,220
And she's going to talk about
our six to 12 month prospectus.

648
00:29:41,220 --> 00:29:41,845
KIRSTEN: Great.

649
00:29:49,380 --> 00:29:50,340
Thanks, Jackson.

650
00:29:50,340 --> 00:29:53,270
So it's important to note
that the Lighting Africa

651
00:29:53,270 --> 00:29:54,770
project doesn't
actually manufacture

652
00:29:54,770 --> 00:29:55,720
photovoltaic devices.

653
00:29:55,720 --> 00:29:59,430
That is they actually cooperate
with small companies which

654
00:29:59,430 --> 00:30:02,040
are risk averse, which means
at least in the next 12 months,

655
00:30:02,040 --> 00:30:04,535
they're interested in the
most established manufacturing

656
00:30:04,535 --> 00:30:05,160
infrastructure.

657
00:30:05,160 --> 00:30:07,290
For that reason, in the
six to 12th month range,

658
00:30:07,290 --> 00:30:09,236
we've just looked at silicon.

659
00:30:09,236 --> 00:30:11,360
So we've compared mono-
and polycrystalline silicon

660
00:30:11,360 --> 00:30:12,410
with amorphous silicon.

661
00:30:12,410 --> 00:30:14,440
Of course, as you all know,
monocrystalline silicon

662
00:30:14,440 --> 00:30:15,856
has a higher
efficiency but, also,

663
00:30:15,856 --> 00:30:17,970
higher price per watt peak.

664
00:30:17,970 --> 00:30:21,160
It's important to note that
in the Lighting Africa project

665
00:30:21,160 --> 00:30:22,895
because the lifetime
of these devices

666
00:30:22,895 --> 00:30:24,770
is not limited by the
photovoltaic component,

667
00:30:24,770 --> 00:30:28,700
but rather by the LED,
the CFL, the battery,

668
00:30:28,700 --> 00:30:30,290
it opens up an
interesting opportunity

669
00:30:30,290 --> 00:30:32,370
in that the photovoltaic
component doesn't

670
00:30:32,370 --> 00:30:34,411
have to last as long as
an installation you might

671
00:30:34,411 --> 00:30:35,610
put on a roof in Cambridge.

672
00:30:35,610 --> 00:30:38,690
It could only, maybe, be three
to five years in lifetime.

673
00:30:38,690 --> 00:30:40,300
And for that reason,
we could decrease

674
00:30:40,300 --> 00:30:42,549
the cost of the encapsulation
materials, the commodity

675
00:30:42,549 --> 00:30:44,420
materials, the glass,
and the backing

676
00:30:44,420 --> 00:30:45,970
that would normally be required.

677
00:30:45,970 --> 00:30:48,417
So amorphous silicon might
be a better opportunity

678
00:30:48,417 --> 00:30:49,250
in this application.

679
00:30:51,580 --> 00:30:54,080
So let's compare crystalline
amorphous for the two consumers

680
00:30:54,080 --> 00:30:55,960
that Jackson mentioned
in the beginning.

681
00:30:55,960 --> 00:30:58,710
For Consumer 1, who's seeking
the lowest cost option,

682
00:30:58,710 --> 00:31:00,560
again, we want an
integrated module

683
00:31:00,560 --> 00:31:02,610
in the solar portable lantern.

684
00:31:02,610 --> 00:31:05,579
So for that reason,
amorphous silicon

685
00:31:05,579 --> 00:31:07,120
doesn't have a high
enough efficiency

686
00:31:07,120 --> 00:31:10,540
to integrate the
device into the SPL.

687
00:31:10,540 --> 00:31:13,036
It would require 400
centimeters squared.

688
00:31:13,036 --> 00:31:14,410
Because the devices
are so small,

689
00:31:14,410 --> 00:31:16,618
we're limiting that to the
crystalline silicon where,

690
00:31:16,618 --> 00:31:20,460
again, you're not going require
as many encapsulation materials

691
00:31:20,460 --> 00:31:22,700
as you would in a roof
insulation in Cambridge.

692
00:31:22,700 --> 00:31:24,144
But, still.

693
00:31:24,144 --> 00:31:26,560
And then, for Consumer 2, who's
seeking higher performance

694
00:31:26,560 --> 00:31:30,740
modules, you could either
use amorphous silicon,

695
00:31:30,740 --> 00:31:33,280
remove the
encapsulation materials,

696
00:31:33,280 --> 00:31:37,290
and have a very large area solar
cell, which you could, again,

697
00:31:37,290 --> 00:31:39,460
bring in and out during the day.

698
00:31:39,460 --> 00:31:41,280
Or it opens up
another opportunity

699
00:31:41,280 --> 00:31:43,730
in that you could use
crystalline silicon,

700
00:31:43,730 --> 00:31:47,960
encapsulate it with standard
glass aluminum frame.

701
00:31:47,960 --> 00:31:50,520
And this photovoltaic
module could actually

702
00:31:50,520 --> 00:31:52,154
exceed the lifetime
of the device.

703
00:31:52,154 --> 00:31:54,320
That is a person could buy
a solar portable lantern,

704
00:31:54,320 --> 00:31:56,410
to which would only last
three to five years,

705
00:31:56,410 --> 00:31:59,230
and replace the SPL later,
replace the LED in the battery

706
00:31:59,230 --> 00:32:03,210
but still use the same
photovoltaic module.

707
00:32:03,210 --> 00:32:05,990
So for both consumers, low
cost and high performance

708
00:32:05,990 --> 00:32:07,780
seeking consumers,
crystalline silicon

709
00:32:07,780 --> 00:32:09,652
presents a better solution.

710
00:32:09,652 --> 00:32:11,110
With that, I'll
pass it off to Ben,

711
00:32:11,110 --> 00:32:13,462
who will talk about the one
to five year prospectus.

712
00:32:13,462 --> 00:32:13,962
So.

713
00:32:27,570 --> 00:32:30,490
BEN: So for the one to
five year time frame,

714
00:32:30,490 --> 00:32:34,340
we looked at two different
technologies, which we've,

715
00:32:34,340 --> 00:32:35,965
well, we considered
crystalline silicon

716
00:32:35,965 --> 00:32:38,182
to offer kind of a
baseline for cost.

717
00:32:38,182 --> 00:32:39,640
And then, we looked
at technologies

718
00:32:39,640 --> 00:32:42,720
where we could achieve
a cost reduction.

719
00:32:42,720 --> 00:32:45,620
We focused on micromorph
silicon thin films

720
00:32:45,620 --> 00:32:48,470
and organic solar cells.

721
00:32:48,470 --> 00:32:52,280
These are both kind of thin
film type technologies.

722
00:32:52,280 --> 00:32:55,742
You might wonder why we didn't
include cad-tel or CIGS.

723
00:32:55,742 --> 00:32:58,460
The reason is because
since they contain cadmium,

724
00:32:58,460 --> 00:33:01,120
they have to be recycled
at the end of their life.

725
00:33:01,120 --> 00:33:04,770
And we don't think that was
very realistic in this context.

726
00:33:04,770 --> 00:33:09,220
So first, I'll talk
about micromorph silicon.

727
00:33:09,220 --> 00:33:13,200
And this is a tandem thin film
cell with amorphous silicon

728
00:33:13,200 --> 00:33:15,180
and microcrystalline silicon.

729
00:33:15,180 --> 00:33:17,790
It's on the verge
of commercialization

730
00:33:17,790 --> 00:33:19,870
within the next few years.

731
00:33:19,870 --> 00:33:22,680
Cost estimates are
about $0.70 a watt.

732
00:33:22,680 --> 00:33:26,610
And efficiency
estimates are about 10%.

733
00:33:26,610 --> 00:33:31,500
So first, we considered
the low cost option.

734
00:33:31,500 --> 00:33:37,210
How inexpensive can we make a
basic solar portable lantern?

735
00:33:37,210 --> 00:33:41,710
So here, you see the
historical cost in 2010.

736
00:33:41,710 --> 00:33:45,650
And then, under
various scenarios

737
00:33:45,650 --> 00:33:49,140
you have the cost
estimates for 2015.

738
00:33:49,140 --> 00:33:50,640
The crystalline
silicon was assumed

739
00:33:50,640 --> 00:33:55,326
to be the same as it is today,
basically a dollar a watt.

740
00:33:55,326 --> 00:33:57,075
Micromorph silicon was
assume to be $0.70.

741
00:33:57,075 --> 00:33:59,530
And then, on the
far right, we have

742
00:33:59,530 --> 00:34:02,750
kind of a really
optimistic scenario where

743
00:34:02,750 --> 00:34:06,620
we've reduced cost even further
by reducing encapsulation

744
00:34:06,620 --> 00:34:09,315
materials just for
this application.

745
00:34:09,315 --> 00:34:12,530
And so we're down
to $0.55 a watt.

746
00:34:12,530 --> 00:34:14,139
What you can see
is that the costs

747
00:34:14,139 --> 00:34:18,340
are going to go down regardless
of what PV platform is used.

748
00:34:18,340 --> 00:34:22,820
And micromorph silicon provides
about a 5% additional cost

749
00:34:22,820 --> 00:34:25,110
decrease compared to
crystalline silicon.

750
00:34:25,110 --> 00:34:27,679
And that doesn't sound
like a lot to us perhaps.

751
00:34:27,679 --> 00:34:33,739
But it's not insignificant
in this context.

752
00:34:33,739 --> 00:34:37,980
Next, we looked at these
high-performance options.

753
00:34:37,980 --> 00:34:40,864
Because since the
cost of the device

754
00:34:40,864 --> 00:34:44,100
is dominated by the
non-PV materials

755
00:34:44,100 --> 00:34:48,159
for these basic devices, as
you add more PV material,

756
00:34:48,159 --> 00:34:52,530
you leverage the
low cost of the PV.

757
00:34:52,530 --> 00:34:57,960
So we split us up into three
different high-performance

758
00:34:57,960 --> 00:35:01,060
products-- the basic, the
medium or multifunctional,

759
00:35:01,060 --> 00:35:03,370
and the ultra high.

760
00:35:03,370 --> 00:35:07,090
And to kind of give you an idea
of what these are capable of,

761
00:35:07,090 --> 00:35:10,580
the basic might
be able to provide

762
00:35:10,580 --> 00:35:14,680
about five hours of light a
day and a cellphone charge.

763
00:35:14,680 --> 00:35:18,150
The medium one could
charge 20 cellphones.

764
00:35:18,150 --> 00:35:22,120
So this could act as a community
sort of cellphone charging

765
00:35:22,120 --> 00:35:23,050
center.

766
00:35:23,050 --> 00:35:25,990
And then, the high-performance
one could even power things

767
00:35:25,990 --> 00:35:29,430
like sewing machines,
TVs, things like this,

768
00:35:29,430 --> 00:35:33,980
so lifestyle changes or
entrepreneurial opportunities.

769
00:35:33,980 --> 00:35:38,460
So now, Rachel will
talk about organic PV.

770
00:35:54,980 --> 00:35:57,730
RACHEL: OK, so the second
low cost alternative

771
00:35:57,730 --> 00:36:00,310
to crystalline silicon, that we
considered in the one to five

772
00:36:00,310 --> 00:36:02,860
year range, was
organic photovoltaics.

773
00:36:02,860 --> 00:36:05,620
And organics are unique because
they're made up entirely

774
00:36:05,620 --> 00:36:07,586
of carbon-based
plastic material, which

775
00:36:07,586 --> 00:36:09,710
means that they're
manufacturing costs can actually

776
00:36:09,710 --> 00:36:12,210
be substantially lower
than that of silicon.

777
00:36:12,210 --> 00:36:16,725
And in fact, they're forecast
only cost $0.50 a watt by 2015.

778
00:36:16,725 --> 00:36:18,629
And unfortunately,
their efficiencies

779
00:36:18,629 --> 00:36:19,420
are less promising.

780
00:36:19,420 --> 00:36:21,680
Because they're
only about 1% to 3%.

781
00:36:21,680 --> 00:36:24,300
But Heliatek, which is
a Dresden based company,

782
00:36:24,300 --> 00:36:27,630
has recently set a new
record for almost 10%

783
00:36:27,630 --> 00:36:29,802
with their tandem organic cell.

784
00:36:29,802 --> 00:36:31,510
So the first thing
we're going to look at

785
00:36:31,510 --> 00:36:36,210
is how organic PV could play
a role in the inexpensive SPL

786
00:36:36,210 --> 00:36:37,540
for the first customer.

787
00:36:37,540 --> 00:36:41,500
And this is a plot of the module
area required for various power

788
00:36:41,500 --> 00:36:42,670
generation capacities.

789
00:36:42,670 --> 00:36:45,880
And it compares 20%
efficient silicon

790
00:36:45,880 --> 00:36:48,790
with 3% and 5%
efficient organic PV.

791
00:36:48,790 --> 00:36:50,300
And basically,
what this shows is

792
00:36:50,300 --> 00:36:53,440
that to generate the same amount
of power as a silicon cell,

793
00:36:53,440 --> 00:36:56,350
you need a substantially
larger area of organics.

794
00:36:56,350 --> 00:36:58,950
Because it's so much less
efficient than the silicon.

795
00:36:58,950 --> 00:37:00,810
So this affects
the first customer.

796
00:37:00,810 --> 00:37:03,780
Because in order just to
generate the 2.5 watts

797
00:37:03,780 --> 00:37:05,890
necessary for the
SPL, you actually

798
00:37:05,890 --> 00:37:08,640
need over 800 square
centimeters of 3%

799
00:37:08,640 --> 00:37:11,289
efficient organic material,
which is not reasonably

800
00:37:11,289 --> 00:37:13,080
something that you
could fit onto a lantern

801
00:37:13,080 --> 00:37:15,230
that you have to
carry around with you.

802
00:37:15,230 --> 00:37:18,280
So because the first customer
requires a solar panel that

803
00:37:18,280 --> 00:37:21,470
could be entirely integrated
onto a handheld device,

804
00:37:21,470 --> 00:37:24,117
its organic PV doesn't really
represent a great option,

805
00:37:24,117 --> 00:37:25,700
at least in the one
to five year term,

806
00:37:25,700 --> 00:37:27,241
because it's
efficiencies are so low.

807
00:37:30,184 --> 00:37:32,100
OK, so the second thing
we're going to look at

808
00:37:32,100 --> 00:37:34,280
is how organic PV
might be useful

809
00:37:34,280 --> 00:37:35,960
to the high-performance
modules that

810
00:37:35,960 --> 00:37:39,490
are entirely separated from
the devices that they charge.

811
00:37:39,490 --> 00:37:41,380
This is the second customer.

812
00:37:41,380 --> 00:37:43,660
So this is a plot
of the manufacturing

813
00:37:43,660 --> 00:37:47,580
cost of the entire device and
versus the power generation

814
00:37:47,580 --> 00:37:48,550
capacity.

815
00:37:48,550 --> 00:37:51,610
And it compares a dollar
per watt silicon with $0.50

816
00:37:51,610 --> 00:37:54,350
and $0.35 per watt organic PV.

817
00:37:54,350 --> 00:37:56,610
And basically, what this
shows-- this is pretty much

818
00:37:56,610 --> 00:37:58,818
the same plot that Ben just
showed except it compares

819
00:37:58,818 --> 00:38:03,230
organics-- is that as we look at
a more high-performance device,

820
00:38:03,230 --> 00:38:06,210
the cost savings, that
you get from switching

821
00:38:06,210 --> 00:38:08,990
from silicon to organics, are
actually quite substantial.

822
00:38:08,990 --> 00:38:13,000
And in fact, for the same cost
as a given silicon device,

823
00:38:13,000 --> 00:38:15,250
you can actually get almost
twice the power generation

824
00:38:15,250 --> 00:38:17,600
capacity by switching
to organics.

825
00:38:17,600 --> 00:38:20,420
So for this reason, and also
because a module area is not

826
00:38:20,420 --> 00:38:21,977
really a constraint
in this context,

827
00:38:21,977 --> 00:38:24,560
because we're just talking about
building a module that you're

828
00:38:24,560 --> 00:38:26,610
going to leave in your
yard, and not carry around

829
00:38:26,610 --> 00:38:29,630
with you on a
lantern, organic PV

830
00:38:29,630 --> 00:38:32,630
is actually an excellent option
as a low cost alternative

831
00:38:32,630 --> 00:38:34,902
to crystalline silicon in
the one to five year range

832
00:38:34,902 --> 00:38:36,235
despite its very low efficiency.

833
00:38:39,530 --> 00:38:42,030
OK, so the conclusions for
the one to five year term,

834
00:38:42,030 --> 00:38:45,200
basically, are that the
manufacturing cost of the SPL

835
00:38:45,200 --> 00:38:47,210
can be moderately
decreased by switching

836
00:38:47,210 --> 00:38:49,420
from crystalline
silicon to micromorph.

837
00:38:49,420 --> 00:38:52,850
And there are greater
cost reductions

838
00:38:52,850 --> 00:38:55,640
available in the higher
performance modules.

839
00:38:55,640 --> 00:38:58,920
Because as the lower costs
of micromorph and organic

840
00:38:58,920 --> 00:39:00,580
PV can be more fully
leveraged as we

841
00:39:00,580 --> 00:39:03,564
consider a device with greater
power generating capacity.

842
00:39:03,564 --> 00:39:05,730
So with that, I will give
it to Ron for the 10-year.

843
00:39:20,400 --> 00:39:24,070
RON : OK, so moving on to the
five to 10 year prospectus,

844
00:39:24,070 --> 00:39:28,130
this had a unique challenge
in that, oftentimes,

845
00:39:28,130 --> 00:39:32,570
research cell modules
will have a huge barrier

846
00:39:32,570 --> 00:39:33,890
to commercialization.

847
00:39:33,890 --> 00:39:36,820
And these are things that the
probability of them actually

848
00:39:36,820 --> 00:39:39,620
realizing commercialization,
in the five to 10 year period,

849
00:39:39,620 --> 00:39:41,390
decreases significantly.

850
00:39:41,390 --> 00:39:44,630
So what we did is we tried to
look at modules that we're not

851
00:39:44,630 --> 00:39:48,160
like thermal photovoltaics or
interband gap transition cells.

852
00:39:48,160 --> 00:39:50,382
Because we were afraid that
the probability of those

853
00:39:50,382 --> 00:39:51,840
actually reaching
commercialization

854
00:39:51,840 --> 00:39:52,940
were very low.

855
00:39:52,940 --> 00:39:54,790
So one option that
stood out to us

856
00:39:54,790 --> 00:39:57,290
was actually an extension of
the one to five year period,

857
00:39:57,290 --> 00:40:01,020
was the mature organics as
the benefits that both Ben

858
00:40:01,020 --> 00:40:03,510
and that Rachel mentioned.

859
00:40:03,510 --> 00:40:09,390
Specifically, that as the
areas of the cell get larger,

860
00:40:09,390 --> 00:40:11,690
they could have a very
good cost leverage.

861
00:40:11,690 --> 00:40:14,130
Because they could power
other household items

862
00:40:14,130 --> 00:40:17,430
such as TV, fans, and radios.

863
00:40:17,430 --> 00:40:18,000
Granted.

864
00:40:18,000 --> 00:40:20,836
also they have extremely
attractive dollar

865
00:40:20,836 --> 00:40:23,210
per watt peak performances
because of their extremely low

866
00:40:23,210 --> 00:40:25,480
cost and moderate performances.

867
00:40:25,480 --> 00:40:27,160
Also, we expect that
commercialization

868
00:40:27,160 --> 00:40:29,600
will be set to begin and that,
actually, the efficiencies

869
00:40:29,600 --> 00:40:32,300
of commercial scale modules
will reach 5% to 8%,

870
00:40:32,300 --> 00:40:36,346
which are actually pretty
good performance modules.

871
00:40:36,346 --> 00:40:37,762
Another thing that
stood out to us

872
00:40:37,762 --> 00:40:40,000
was actually cadmium-free
CIGS technology.

873
00:40:40,000 --> 00:40:43,560
And as Ben mentioned, cadmium
has a huge environmental impact

874
00:40:43,560 --> 00:40:46,820
and would require a recycling
process, which is not practical

875
00:40:46,820 --> 00:40:48,120
given this context.

876
00:40:48,120 --> 00:40:50,690
So we looked at a
cadmium-free CIGS technology

877
00:40:50,690 --> 00:40:52,849
that would actually have
the benefits of thin films

878
00:40:52,849 --> 00:40:54,640
in their low cost and
moderate performance,

879
00:40:54,640 --> 00:40:56,890
but not have the actual
environmental concerns

880
00:40:56,890 --> 00:40:58,330
associated with them.

881
00:40:58,330 --> 00:41:02,550
So currently, in lab, there
have been a few options

882
00:41:02,550 --> 00:41:04,790
to replace the cadmium
sulfide buffer layer.

883
00:41:04,790 --> 00:41:07,530
There's been zinc oxide,
and also zinc indium

884
00:41:07,530 --> 00:41:13,170
selenide compounds that can,
actually, be grown epitaxially

885
00:41:13,170 --> 00:41:15,570
in the manufacturing
process, making

886
00:41:15,570 --> 00:41:17,760
it really easy for
roll-to-roll processing.

887
00:41:17,760 --> 00:41:22,640
So currently, in the
research cell modules,

888
00:41:22,640 --> 00:41:25,100
they are reaching about 10%
to 12% efficiencies, which

889
00:41:25,100 --> 00:41:27,110
is really promising
given they're actually,

890
00:41:27,110 --> 00:41:29,250
it hasn't been
studied for that long.

891
00:41:29,250 --> 00:41:32,270
So we expect that in the
five to 10 year period,

892
00:41:32,270 --> 00:41:36,880
we could actually realize this
high-efficiency cadmium-free

893
00:41:36,880 --> 00:41:40,270
CIG cells, especially since
manufacturing processes have

894
00:41:40,270 --> 00:41:44,390
already been developed
for the CIGS cells.

895
00:41:44,390 --> 00:41:47,590
So for the long-term
conclusions,

896
00:41:47,590 --> 00:41:50,510
we think that the cadmium-free
CIGS modules be great

897
00:41:50,510 --> 00:41:54,190
for Consumer 1 because of
their moderate performance

898
00:41:54,190 --> 00:41:58,710
and their attractive dollar
per watt peak metrics,

899
00:41:58,710 --> 00:42:01,430
making them, actually,
integratable on a small area,

900
00:42:01,430 --> 00:42:04,920
and providing the 2.5
watts for the SPL.

901
00:42:04,920 --> 00:42:07,390
For Consumer 2, we
actually thought

902
00:42:07,390 --> 00:42:10,910
a large, mature organics
module in their backyard

903
00:42:10,910 --> 00:42:13,250
would be great because
of their really low cost,

904
00:42:13,250 --> 00:42:15,980
and also because
of their ability

905
00:42:15,980 --> 00:42:20,060
to possibly charge
other household devices

906
00:42:20,060 --> 00:42:22,810
as their performance increases.

907
00:42:22,810 --> 00:42:24,820
And these are, basically,
the conclusions

908
00:42:24,820 --> 00:42:26,570
of all my other
colleagues in front of me.

909
00:42:26,570 --> 00:42:28,690
The six to 12 month mono-
and multicrystalline

910
00:42:28,690 --> 00:42:30,020
are the best options.

911
00:42:30,020 --> 00:42:32,430
In the one to five year
period, micromorph and organics

912
00:42:32,430 --> 00:42:33,880
will play a larger role.

913
00:42:33,880 --> 00:42:37,170
And in the five to 10
year, organics and CF CIGS

914
00:42:37,170 --> 00:42:39,390
stand out as very
attractive options.

915
00:42:39,390 --> 00:42:42,560
So in conclusion, next
generation photovoltaic

916
00:42:42,560 --> 00:42:45,140
technologies definitely have
the capability, especially as

917
00:42:45,140 --> 00:42:47,210
alternatives to current
crystalline technology,

918
00:42:47,210 --> 00:42:50,275
to provide a green and positive
difference in the Lighting

919
00:42:50,275 --> 00:42:50,900
Africa project.

920
00:42:53,620 --> 00:42:55,096
[APPLAUSE]

921
00:43:01,589 --> 00:43:03,214
AUDIENCE: Have you
worked with anybody,

922
00:43:03,214 --> 00:43:06,860
like D-Lab or any other
nonprofits that have

923
00:43:06,860 --> 00:43:08,110
done this kind of work before?

924
00:43:08,110 --> 00:43:10,570
Because, sometimes, it's
about the relationships

925
00:43:10,570 --> 00:43:12,538
that you can build
with the companies,

926
00:43:12,538 --> 00:43:16,240
the kind of discounted products
that they can give you.

927
00:43:16,240 --> 00:43:18,770
And that's, sometimes,
kind of takes over.

928
00:43:18,770 --> 00:43:20,854
JACKSON: Yeah, so, I guess,
we skipped this slide.

929
00:43:20,854 --> 00:43:21,811
Or we didn't get to it.

930
00:43:21,811 --> 00:43:23,810
But we actually worked
with the World Bank,

931
00:43:23,810 --> 00:43:25,842
the Lighting Africa is
with the World Bank.

932
00:43:25,842 --> 00:43:27,300
We also worked with
people who were

933
00:43:27,300 --> 00:43:29,280
working on it at Humboldt
State University,

934
00:43:29,280 --> 00:43:31,410
and talked a lot to them.

935
00:43:31,410 --> 00:43:33,490
And right now, so one
thing that's important

936
00:43:33,490 --> 00:43:35,200
is that the Lighting
Africa project

937
00:43:35,200 --> 00:43:38,830
is, they provide a lot of
education and information

938
00:43:38,830 --> 00:43:39,410
to companies.

939
00:43:39,410 --> 00:43:40,826
But the companies
are the one that

940
00:43:40,826 --> 00:43:42,724
actually build the devices.

941
00:43:42,724 --> 00:43:44,015
Does that answer your question?

942
00:43:44,015 --> 00:43:45,166
AUDIENCE: So it's
up to the companies

943
00:43:45,166 --> 00:43:46,160
to decide which one [INAUDIBLE].

944
00:43:46,160 --> 00:43:47,118
JACKSON: Exactly, yeah.

945
00:43:47,118 --> 00:43:50,470
And so the Lighting Africa
provides information to them.

946
00:43:50,470 --> 00:43:53,410
And our report will be provided
to the companies as well.

947
00:43:53,410 --> 00:43:55,840
But in the end, it's
up to them to decide

948
00:43:55,840 --> 00:43:56,942
what's most profitable.

949
00:43:56,942 --> 00:43:58,927
KIRSTEN: And also,
there's several companies

950
00:43:58,927 --> 00:44:00,760
that the Lighting Africa
project works with.

951
00:44:00,760 --> 00:44:06,550
And each company provides a
slightly different solution.

952
00:44:06,550 --> 00:44:09,940
So there's a whole spectrum of
the number of watts you have,

953
00:44:09,940 --> 00:44:11,856
the number of kilowatt hours.

954
00:44:11,856 --> 00:44:13,772
So there are several
different solutions based

955
00:44:13,772 --> 00:44:14,897
on the different companies.

956
00:44:17,578 --> 00:44:19,542
AUDIENCE: So when
[INAUDIBLE] dollar

957
00:44:19,542 --> 00:44:23,402
per watt, what about thermal
degradation for all [INAUDIBLE]

958
00:44:23,402 --> 00:44:24,943
that could be a
major problem, right?

959
00:44:24,943 --> 00:44:29,362
I mean, like [INAUDIBLE] itself,
I mean, that's why they're not,

960
00:44:29,362 --> 00:44:30,835
I think, [INAUDIBLE].

961
00:44:33,790 --> 00:44:37,180
RON : So what's, actually,
really positive about this

962
00:44:37,180 --> 00:44:39,890
project is that we're not
really looking for high lifetime

963
00:44:39,890 --> 00:44:40,390
devices.

964
00:44:40,390 --> 00:44:43,290
So it's, actually,
limited by the batteries

965
00:44:43,290 --> 00:44:44,990
and by the other
components of the SPL.

966
00:44:44,990 --> 00:44:47,240
So that's only, they only
have about two to three year

967
00:44:47,240 --> 00:44:47,860
lifetime.

968
00:44:47,860 --> 00:44:51,270
So we think that even though,
obviously, Africa's hot,

969
00:44:51,270 --> 00:44:53,410
there the thermal
degradation will actually not

970
00:44:53,410 --> 00:44:56,080
be the limiting
factor in this case,

971
00:44:56,080 --> 00:44:58,555
especially if they're
encapsulated with relative--

972
00:44:58,555 --> 00:45:01,520
AUDIENCE: So that could
increase the cost, right?

973
00:45:01,520 --> 00:45:03,850
RON : No, actually
if you reduce,

974
00:45:03,850 --> 00:45:07,150
since the cost is dominated
by non-PV materials,

975
00:45:07,150 --> 00:45:10,890
we could actually reduce the
encapsulant costs significantly

976
00:45:10,890 --> 00:45:14,749
and still have a
relatively good lifetime.

977
00:45:14,749 --> 00:45:16,790
AUDIENCE: So could you
comment on that, actually,

978
00:45:16,790 --> 00:45:17,360
a little bit?

979
00:45:17,360 --> 00:45:19,193
What kind of lifetimes
would you expect out

980
00:45:19,193 --> 00:45:22,260
of the current
production organic cells?

981
00:45:22,260 --> 00:45:23,620
RON : [INAUDIBLE]

982
00:45:23,620 --> 00:45:25,260
JACKSON: Yeah, Rachel.

983
00:45:25,260 --> 00:45:26,670
[LAUGHTER]

984
00:45:27,610 --> 00:45:30,910
RACHEL: OK, great.

985
00:45:30,910 --> 00:45:35,060
So, oftentimes, you'll find that
current commercialized organic

986
00:45:35,060 --> 00:45:36,924
cells only last a
couple of days actually.

987
00:45:36,924 --> 00:45:39,340
Although it has been proven
that certain cells can last up

988
00:45:39,340 --> 00:45:42,674
to three years, which would be
sufficient for the lifetimes

989
00:45:42,674 --> 00:45:43,590
that we're looking at.

990
00:45:43,590 --> 00:45:45,947
And this is also in the
one to five year range.

991
00:45:45,947 --> 00:45:47,780
We're not talking about
doing this tomorrow.

992
00:45:47,780 --> 00:45:51,740
So, hopefully,
that sort of metric

993
00:45:51,740 --> 00:45:53,772
would be improved
within that time frame.

994
00:45:53,772 --> 00:45:55,230
AUDIENCE: And you
guys have a sense

995
00:45:55,230 --> 00:45:58,232
is it an encapsulation challenge
or a fundamental materials

996
00:45:58,232 --> 00:45:59,224
challenge?

997
00:45:59,224 --> 00:46:00,216
RACHEL: I think it's a
fundamental materials

998
00:46:00,216 --> 00:46:00,716
challenge.

999
00:46:00,716 --> 00:46:01,733
It's the actual--

1000
00:46:01,733 --> 00:46:03,316
JACKSON: Yeah, and
this actually gives

1001
00:46:03,316 --> 00:46:05,550
a great place for organics
because of our time frame.

1002
00:46:05,550 --> 00:46:08,960
Usually in the US
or, the modules last

1003
00:46:08,960 --> 00:46:10,140
for 20 or 30 years.

1004
00:46:10,140 --> 00:46:11,640
But here, the
lifetime of the device

1005
00:46:11,640 --> 00:46:13,056
is really two or three years.

1006
00:46:13,056 --> 00:46:15,390
So it's a great
opportunity for organics.

1007
00:46:15,390 --> 00:46:17,015
KIRSTEN: Yeah, and
then the opportunity

1008
00:46:17,015 --> 00:46:18,370
for decreasing module costs.

1009
00:46:18,370 --> 00:46:20,370
It just doesn't go all
the way across the board.

1010
00:46:20,370 --> 00:46:23,520
It's more important for
silicon than organics.

1011
00:46:23,520 --> 00:46:27,480
Because, again, organics
aren't as [INAUDIBLE].

1012
00:46:27,480 --> 00:46:31,869
RON : And also I know that
hydrolysis of the carbon-based

1013
00:46:31,869 --> 00:46:33,410
compounds is one of
the big problems.

1014
00:46:33,410 --> 00:46:35,055
So they're really
not good for, like,

1015
00:46:35,055 --> 00:46:36,305
relatively humid environments.

1016
00:46:36,305 --> 00:46:37,390
And in this case,
we're going to be

1017
00:46:37,390 --> 00:46:38,877
in the sub-Saharan
African desert.

1018
00:46:38,877 --> 00:46:40,460
So it's going, that
won't be an issue.

1019
00:46:43,630 --> 00:46:48,110
AUDIENCE: Did you, do you have
any idea about what market,

1020
00:46:48,110 --> 00:46:50,563
what the size of
the market would

1021
00:46:50,563 --> 00:46:53,942
be for different possible
costs that you outlined

1022
00:46:53,942 --> 00:46:55,910
on some of those line graphs?

1023
00:46:55,910 --> 00:47:00,210
Say your total lantern
cost is $40 or something.

1024
00:47:00,210 --> 00:47:05,620
How many people can buy it
if that's what the price is?

1025
00:47:05,620 --> 00:47:08,625
KIRSTEN: So we've, the
top 10% of the population

1026
00:47:08,625 --> 00:47:12,897
in sub-Saharan Africa
earns 40% of the GDP.

1027
00:47:12,897 --> 00:47:15,230
So there would be very few
people in the second customer

1028
00:47:15,230 --> 00:47:16,220
bracket.

1029
00:47:16,220 --> 00:47:18,740
Whereas, most people, I guess,
earn less than a dollar a day

1030
00:47:18,740 --> 00:47:22,260
and would be our target
for the first archetypal,

1031
00:47:22,260 --> 00:47:24,024
as the first
archetypal customer.

1032
00:47:24,024 --> 00:47:26,440
AUDIENCE: So if most of the
people earn less than a dollar

1033
00:47:26,440 --> 00:47:31,010
a day, are they going to save
up couple months of income

1034
00:47:31,010 --> 00:47:34,056
somehow in order to
buy a $30 lantern.

1035
00:47:34,056 --> 00:47:35,720
That's what I'm asking.

1036
00:47:35,720 --> 00:47:38,870
JACKSON: Yeah, so currently,
the buy back time on these

1037
00:47:38,870 --> 00:47:39,840
are about eight months.

1038
00:47:39,840 --> 00:47:41,760
So it's very significant.

1039
00:47:41,760 --> 00:47:44,030
And that's why there's not
widespread proliferation.

1040
00:47:44,030 --> 00:47:45,780
But right now, the
Lighting Africa project

1041
00:47:45,780 --> 00:47:47,890
is working on education.

1042
00:47:47,890 --> 00:47:49,380
And in areas that
they've started

1043
00:47:49,380 --> 00:47:52,004
these educational programs, the
proliferation of these products

1044
00:47:52,004 --> 00:47:53,580
have actually
increased dramatically.

1045
00:47:53,580 --> 00:47:55,950
And people have started saving
up for them, and buying them.

1046
00:47:55,950 --> 00:47:58,660
And actually, there's one of the
main problems with the project

1047
00:47:58,660 --> 00:48:00,190
that there's a wide
scale, there's,

1048
00:48:00,190 --> 00:48:01,731
like, Chinese
companies that come in.

1049
00:48:01,731 --> 00:48:04,490
And they'll sell very,
very cheap devices

1050
00:48:04,490 --> 00:48:05,880
that are extremely shoddy.

1051
00:48:05,880 --> 00:48:07,609
They last maybe a few
weeks or something.

1052
00:48:07,609 --> 00:48:08,650
And they're really cheap.

1053
00:48:08,650 --> 00:48:10,570
But they don't really
do too much good.

1054
00:48:10,570 --> 00:48:13,130
So increasing
education about those,

1055
00:48:13,130 --> 00:48:17,770
and the Lighting Africa project
gives certification of devices

1056
00:48:17,770 --> 00:48:19,110
that will last a few years.

1057
00:48:19,110 --> 00:48:21,380
And so increasing
education and decreasing

1058
00:48:21,380 --> 00:48:24,968
buy back time, which is one of
the main things we'll increase.

1059
00:48:24,968 --> 00:48:27,000
AUDIENCE: Sounds like
you do consumer reports.

1060
00:48:27,000 --> 00:48:28,250
JACKSON: Yeah.

1061
00:48:28,250 --> 00:48:29,950
RON : And also,
one of the, I mean,

1062
00:48:29,950 --> 00:48:31,820
this is actually more
towards customer too.

1063
00:48:31,820 --> 00:48:34,720
But one of the positive
things about this project

1064
00:48:34,720 --> 00:48:37,830
is that communities could pool
resources together and actually

1065
00:48:37,830 --> 00:48:41,306
have their household
items be charged together

1066
00:48:41,306 --> 00:48:43,556
in one person's house, in
the middle of the community.

1067
00:48:43,556 --> 00:48:45,807
Could have that.

1068
00:48:45,807 --> 00:48:47,390
AUDIENCE: Yeah, I
have a question sort

1069
00:48:47,390 --> 00:48:49,790
of like all these lights
I'm assuming use batteries,

1070
00:48:49,790 --> 00:48:52,430
like the cadmium batteries
or [? lithium ?] batteries,

1071
00:48:52,430 --> 00:48:54,210
and so on, so forth.

1072
00:48:54,210 --> 00:48:55,700
And those are
hazardous materials.

1073
00:48:55,700 --> 00:48:58,290
And I'm sure they're either
dealing with them or they

1074
00:48:58,290 --> 00:48:59,170
aren't.

1075
00:48:59,170 --> 00:49:03,280
So given that fact, doesn't
that make your assumption

1076
00:49:03,280 --> 00:49:06,190
that you ruled out
cad-tel or CIGS

1077
00:49:06,190 --> 00:49:09,112
cells to be incorrect
in that you already

1078
00:49:09,112 --> 00:49:12,315
have hazardous materials
in the batteries.

1079
00:49:12,315 --> 00:49:12,940
JACKSON: Right.

1080
00:49:12,940 --> 00:49:14,670
So right now, I
think, for the most,

1081
00:49:14,670 --> 00:49:16,840
they are [INAUDIBLE]
in these batteries.

1082
00:49:16,840 --> 00:49:20,620
Most of the batteries are
fairly well sealed and such.

1083
00:49:20,620 --> 00:49:24,520
But I think, ethically,
we couldn't suggest

1084
00:49:24,520 --> 00:49:26,171
more hazardous materials.

1085
00:49:26,171 --> 00:49:28,420
And so you're saying that
just because there's already

1086
00:49:28,420 --> 00:49:30,740
a problem, why don't we
just add another one.

1087
00:49:30,740 --> 00:49:33,974
I don't think that's
necessarily a good option.

1088
00:49:33,974 --> 00:49:35,515
But you're right
about the batteries.

1089
00:49:38,054 --> 00:49:40,470
AUDIENCE: So for your tier one
customer, your lower income

1090
00:49:40,470 --> 00:49:43,114
customer, you're pretty much
only providing them lighting.

1091
00:49:43,114 --> 00:49:43,780
Is that correct?

1092
00:49:43,780 --> 00:49:44,320
Or do you think--

1093
00:49:44,320 --> 00:49:44,630
JACKSON: Right.

1094
00:49:44,630 --> 00:49:46,004
AUDIENCE: --that
there's options?

1095
00:49:46,004 --> 00:49:50,250
I mean, you have a lot of
graphs that had area of device

1096
00:49:50,250 --> 00:49:53,270
in cost, and for the
different technologies.

1097
00:49:53,270 --> 00:49:54,890
Do you have any
idea, if I wanted

1098
00:49:54,890 --> 00:49:56,270
to charge a
cellphone, where we'd

1099
00:49:56,270 --> 00:49:57,701
have to lie on those graphs?

1100
00:49:57,701 --> 00:49:58,242
RACHEL: Yeah.

1101
00:49:58,242 --> 00:50:01,411
It's a good question.

1102
00:50:01,411 --> 00:50:02,661
JACKSON: [INAUDIBLE] appendix.

1103
00:50:02,661 --> 00:50:04,327
KIRSTEN: Should we
skip to the appendix?

1104
00:50:04,327 --> 00:50:05,610
RON: Yeah, of course.

1105
00:50:05,610 --> 00:50:07,450
BEN: Yeah, so
charging a cellphone--

1106
00:50:07,450 --> 00:50:09,180
AUDIENCE: I mean, so if you
want lighting and cellphone,

1107
00:50:09,180 --> 00:50:10,638
how much does that
add to the cost?

1108
00:50:10,638 --> 00:50:11,350
BEN: Yeah.

1109
00:50:11,350 --> 00:50:13,184
AUDIENCE: Is there a
larger market for that?

1110
00:50:13,184 --> 00:50:15,349
BEN: So there could be a
very large market for that.

1111
00:50:15,349 --> 00:50:17,525
Because it doesn't, actually,
take that much energy.

1112
00:50:17,525 --> 00:50:21,790
It takes about four watt-hours
to charge a cellphone.

1113
00:50:21,790 --> 00:50:25,460
So for a very basic
device that maybe produces

1114
00:50:25,460 --> 00:50:30,800
nine watt-hours a day, you
could get five hours of light,

1115
00:50:30,800 --> 00:50:33,420
for instance, depending on
the efficiency of your LED,

1116
00:50:33,420 --> 00:50:35,360
and, then, also
charge a cellphone.

1117
00:50:35,360 --> 00:50:38,795
So it's actually, it's
not a great threshold

1118
00:50:38,795 --> 00:50:41,720
to overcome to be able to
charge other things, especially

1119
00:50:41,720 --> 00:50:42,220
cellphones.

1120
00:50:42,220 --> 00:50:44,774
JACKSON: And the non-PV
aspect of the cellphone charge

1121
00:50:44,774 --> 00:50:46,092
is also very cheap.

1122
00:50:51,526 --> 00:50:53,500
AUDIENCE: Could you
please comment again

1123
00:50:53,500 --> 00:50:56,380
on why you say that, or do
you see higher potential

1124
00:50:56,380 --> 00:50:59,550
in organics for the
one to five year period

1125
00:50:59,550 --> 00:51:03,650
than in cadmium-free CIGS cells?

1126
00:51:03,650 --> 00:51:07,864
So why did you get
to the conclusion

1127
00:51:07,864 --> 00:51:10,925
to recommend organics
for the one to five

1128
00:51:10,925 --> 00:51:12,834
and CIGS for the longer term?

1129
00:51:12,834 --> 00:51:14,250
RON: We wanted to
be conservative.

1130
00:51:14,250 --> 00:51:17,440
And cadmium-free
CIG cells have only

1131
00:51:17,440 --> 00:51:21,340
been recently not
discovered, but researched

1132
00:51:21,340 --> 00:51:22,634
in the past year or two.

1133
00:51:22,634 --> 00:51:25,050
So we wanted to be kind of
conservative with our estimates

1134
00:51:25,050 --> 00:51:26,150
and take into account
that there might

1135
00:51:26,150 --> 00:51:27,930
be big hurdles to
commercialization.

1136
00:51:27,930 --> 00:51:29,596
So we put in the five
to 10 year period.

1137
00:51:32,535 --> 00:51:34,265
Thanks.

1138
00:51:34,265 --> 00:51:36,014
AUDIENCE: So one of
the interesting things

1139
00:51:36,014 --> 00:51:39,162
about electricity generation
in Africa, it seems,

1140
00:51:39,162 --> 00:51:40,960
is the lack of a legacy system.

1141
00:51:40,960 --> 00:51:43,236
And so you really do have
this question of like,

1142
00:51:43,236 --> 00:51:45,777
what is the most cost effective
way of delivering power today

1143
00:51:45,777 --> 00:51:48,277
rather than what's the most
cost effective way of delivering

1144
00:51:48,277 --> 00:51:49,820
power when you have
electricity grid?

1145
00:51:49,820 --> 00:51:52,100
But what, do you guys
have a sense of sort

1146
00:51:52,100 --> 00:51:54,892
of the cost per person at
which electrification by grid

1147
00:51:54,892 --> 00:51:56,860
becomes a compelling
thing to do?

1148
00:52:00,274 --> 00:52:02,440
JACKSON: Yeah, that sounds
something we looked into.

1149
00:52:02,440 --> 00:52:05,500
[LAUGHTER]

1150
00:52:05,500 --> 00:52:09,090
JACKSON: Definitely, I think
the cost would be pretty high,

1151
00:52:09,090 --> 00:52:10,580
at least compared
to these devices.

1152
00:52:10,580 --> 00:52:12,930
I mean, of course, you
have a lot of, it's very,

1153
00:52:12,930 --> 00:52:16,180
very spread out, and a lot
of small villages, and what

1154
00:52:16,180 --> 00:52:18,490
not, which these are
targeted towards.

1155
00:52:18,490 --> 00:52:20,630
One of the other ideas,
one of the other concepts

1156
00:52:20,630 --> 00:52:23,520
that was looked at was
a larger scale version

1157
00:52:23,520 --> 00:52:27,850
of this where you have a
large PVA ray or a few panels

1158
00:52:27,850 --> 00:52:29,720
in the city or the city center.

1159
00:52:29,720 --> 00:52:31,940
And then, all the villagers
could come in and charge

1160
00:52:31,940 --> 00:52:32,939
your batteries that way.

1161
00:52:32,939 --> 00:52:35,260
And they all have
little [INAUDIBLE],

1162
00:52:35,260 --> 00:52:39,730
which was another model
that is being looked at.

1163
00:52:39,730 --> 00:52:41,890
AUDIENCE: So it sounds
like what you're

1164
00:52:41,890 --> 00:52:46,260
saying is that if you push
more towards concentrated

1165
00:52:46,260 --> 00:52:50,350
populations, then the
hereto kind of becomes

1166
00:52:50,350 --> 00:52:52,525
more favorable where
you can have larger

1167
00:52:52,525 --> 00:52:54,654
installations and
central locations

1168
00:52:54,654 --> 00:52:57,668
that communities pool
together and share.

1169
00:52:57,668 --> 00:52:59,334
JACKSON: Yeah, that's
where we're going.

1170
00:52:59,334 --> 00:53:01,250
BEN: Yeah, there's two
different demographics.

1171
00:53:01,250 --> 00:53:03,815
So you have your
off-grid suburban.

1172
00:53:03,815 --> 00:53:07,440
And then, you have
off-grid very rural.

1173
00:53:07,440 --> 00:53:13,890
So often, in the relatively high
income bracket, the tier two,

1174
00:53:13,890 --> 00:53:16,400
these are people living in kind
of off-grid suburban areas.

1175
00:53:16,400 --> 00:53:19,109
There just outskirts of
cities and things like that.

1176
00:53:19,109 --> 00:53:20,650
JACKSON: And another
thing, actually,

1177
00:53:20,650 --> 00:53:24,290
is that we talk
about off-grid a lot.

1178
00:53:24,290 --> 00:53:27,060
But the actual grid
in Africa is so poor

1179
00:53:27,060 --> 00:53:29,470
that these products are actually
very applicable to them.

1180
00:53:29,470 --> 00:53:34,640
Some people have
blackouts daily or weekly,

1181
00:53:34,640 --> 00:53:37,120
such that these devices
become necessary as well.

1182
00:53:42,882 --> 00:53:45,090
PROFESSOR: All right, let's
thank our speakers again.

1183
00:53:45,090 --> 00:53:46,584
[APPLAUSE]

1184
00:53:50,241 --> 00:53:51,365
STUDENT 1: So hi, everyone.

1185
00:53:51,365 --> 00:53:52,910
We are Team 6.

1186
00:53:52,910 --> 00:53:55,980
And we are going to talk about
the potential of simulation

1187
00:53:55,980 --> 00:54:00,150
softwares to predict the
photovoltaic performances.

1188
00:54:00,150 --> 00:54:04,160
And our team members are
[INAUDIBLE], Noami, myself,

1189
00:54:04,160 --> 00:54:06,040
[INAUDIBLE], and Omar, here.

1190
00:54:09,040 --> 00:54:12,710
OK, so this is the
figure that you guys

1191
00:54:12,710 --> 00:54:15,140
are very much familiar with.

1192
00:54:15,140 --> 00:54:19,770
So we all do know that
silicon solar cells show

1193
00:54:19,770 --> 00:54:24,800
the benefit of high efficiency,
whereas the efficiency

1194
00:54:24,800 --> 00:54:27,880
of the thin film, or
emerging photovoltaics,

1195
00:54:27,880 --> 00:54:29,340
are relatively low.

1196
00:54:29,340 --> 00:54:32,550
But they are definitely
under a spotlight.

1197
00:54:32,550 --> 00:54:36,870
Because they do
have the advantage

1198
00:54:36,870 --> 00:54:41,090
over the silicon such as
higher absorption efficient,

1199
00:54:41,090 --> 00:54:45,400
and lower manufacturing
costs, and the flexibility.

1200
00:54:45,400 --> 00:54:49,750
So we are going to simulate
based on the materials used

1201
00:54:49,750 --> 00:54:53,040
in these types of solar cells.

1202
00:54:53,040 --> 00:54:56,000
So our model, in
general, because they

1203
00:54:56,000 --> 00:54:59,840
do have a lot of benefits,
such as it is very much useful.

1204
00:54:59,840 --> 00:55:02,870
But it is impossible or
impractical to create

1205
00:55:02,870 --> 00:55:04,814
certain experimental conditions.

1206
00:55:04,814 --> 00:55:06,230
And also, [? doing ?]
assimilation

1207
00:55:06,230 --> 00:55:10,320
is much more efficient in
terms of money and time taken.

1208
00:55:10,320 --> 00:55:12,480
And also, we can do the
fundamental and simple

1209
00:55:12,480 --> 00:55:16,540
understanding at a very small
scale such as atomic scale.

1210
00:55:16,540 --> 00:55:19,420
But there's one very
critical limitation.

1211
00:55:19,420 --> 00:55:21,420
That is the accuracy problem.

1212
00:55:21,420 --> 00:55:26,060
So this means in many
cases, the accuracy matters.

1213
00:55:26,060 --> 00:55:31,800
Like it's not really accurate
as the [INAUDIBLE] happens.

1214
00:55:31,800 --> 00:55:36,230
So the system to be modeled
will be explained in detail

1215
00:55:36,230 --> 00:55:37,230
by following speaker.

1216
00:55:37,230 --> 00:55:41,340
However, if I speak,
if I say very briefly,

1217
00:55:41,340 --> 00:55:43,630
it can be divided into three.

1218
00:55:43,630 --> 00:55:47,870
First, all organic such
as P3HT and PCBM system.

1219
00:55:47,870 --> 00:55:52,175
And the second one is all
inorganic, such as lead

1220
00:55:52,175 --> 00:55:54,880
sulfide quantum dot and
titanium [? fullerene. ?]

1221
00:55:54,880 --> 00:55:59,000
And the last one is some
combination of those, so called

1222
00:55:59,000 --> 00:56:00,580
hybrid cells.

1223
00:56:00,580 --> 00:56:06,020
So our aims here, our first, we
are going to introduce the two

1224
00:56:06,020 --> 00:56:08,590
simulation packages
and, then, followed

1225
00:56:08,590 --> 00:56:13,330
by the comparison of the
performance by, sorry,

1226
00:56:13,330 --> 00:56:15,850
performance from the
simulation with the values

1227
00:56:15,850 --> 00:56:17,280
from the literature.

1228
00:56:17,280 --> 00:56:19,460
And in the detailed
study section,

1229
00:56:19,460 --> 00:56:23,260
we basically change everything
in the simulation package,

1230
00:56:23,260 --> 00:56:25,680
such as layer
thickness, temperature,

1231
00:56:25,680 --> 00:56:30,490
band energy levels including
the electron affinity and band

1232
00:56:30,490 --> 00:56:32,850
gaps, and lastly,
the carrier mobility.

1233
00:56:32,850 --> 00:56:35,880
And then, the presentation
will be concluded

1234
00:56:35,880 --> 00:56:37,790
with sensitivity studies here.

1235
00:56:50,060 --> 00:56:51,980
STUDENT 2: So the
question raised

1236
00:56:51,980 --> 00:56:54,870
as to which simulation
packages we should use.

1237
00:56:54,870 --> 00:56:57,300
So you all are
familiar with PC1D,

1238
00:56:57,300 --> 00:57:01,440
which is industry standard for
simulating crystalline silicon.

1239
00:57:01,440 --> 00:57:05,050
However, given that we're
simulating organic materials,

1240
00:57:05,050 --> 00:57:08,120
inorganic materials
at very low transport,

1241
00:57:08,120 --> 00:57:12,840
we opted to go with more
generic simulators called AMPS,

1242
00:57:12,840 --> 00:57:16,080
from Penn State
University, and SCAPS.

1243
00:57:16,080 --> 00:57:19,150
And I'll discuss why.

1244
00:57:19,150 --> 00:57:22,280
So with these organic
materials, and these thin film

1245
00:57:22,280 --> 00:57:26,290
materials, traps and
recombination are a huge issue.

1246
00:57:26,290 --> 00:57:30,270
And the question arises as
to how to model these traps.

1247
00:57:30,270 --> 00:57:33,340
So at the highest level
of abstraction, that most

1248
00:57:33,340 --> 00:57:36,980
top-level view, you can just
look at the bulk recombination

1249
00:57:36,980 --> 00:57:40,620
time and simulate with that,
which is the approach that's

1250
00:57:40,620 --> 00:57:43,710
used by PC1D.

1251
00:57:43,710 --> 00:57:45,310
The second level
of abstraction is

1252
00:57:45,310 --> 00:57:47,540
to break up your bulk
recombination times

1253
00:57:47,540 --> 00:57:49,900
into the different components.

1254
00:57:49,900 --> 00:57:53,040
And in particular,
Shockley-Read-Hawk

1255
00:57:53,040 --> 00:57:55,990
recombination is very
important for these materials.

1256
00:57:55,990 --> 00:57:59,390
So as you remember from
class, you basically

1257
00:57:59,390 --> 00:58:01,680
have traps between your
conduction band and valence

1258
00:58:01,680 --> 00:58:02,370
band.

1259
00:58:02,370 --> 00:58:05,470
You have [? curves ?] that
are in these two bands.

1260
00:58:05,470 --> 00:58:07,540
And when they recombine,
that effectively

1261
00:58:07,540 --> 00:58:08,500
reduces your current.

1262
00:58:11,040 --> 00:58:14,450
So both AMPS and
SCAPS actually allow

1263
00:58:14,450 --> 00:58:19,040
for simulating these
physical traps.

1264
00:58:19,040 --> 00:58:22,330
So you can simulate it
with-- and these traps

1265
00:58:22,330 --> 00:58:25,310
have different spectrums
with respect to energy.

1266
00:58:25,310 --> 00:58:28,830
So for example, you can have
traps that decay exponentially

1267
00:58:28,830 --> 00:58:30,190
from the band edges.

1268
00:58:30,190 --> 00:58:32,660
Or you can just have
discrete level traps

1269
00:58:32,660 --> 00:58:35,210
that are certain energy level.

1270
00:58:35,210 --> 00:58:38,400
And you can have traps that
have a Gaussian distribution.

1271
00:58:38,400 --> 00:58:41,740
Both AMPS and SCAPS
allow for that.

1272
00:58:41,740 --> 00:58:46,080
At the same time, SCAPS allows
for spatial non-uniformities

1273
00:58:46,080 --> 00:58:47,040
for traps.

1274
00:58:47,040 --> 00:58:50,060
So for example, let's
say if I have a layer,

1275
00:58:50,060 --> 00:58:52,050
and at the top layer,
there's a lot of traps.

1276
00:58:52,050 --> 00:58:54,250
But by the time, by the
bottom of the layer,

1277
00:58:54,250 --> 00:58:58,800
there aren't that many traps,
I can model that in SCAPS.

1278
00:58:58,800 --> 00:59:01,640
However in AMPS, I
only have, I can only

1279
00:59:01,640 --> 00:59:04,860
model a uniform distribution
of traps spatially.

1280
00:59:04,860 --> 00:59:07,400
So I can't have any Gaussian
distributions or anything

1281
00:59:07,400 --> 00:59:08,110
like that.

1282
00:59:11,080 --> 00:59:15,930
The second key component for
solar cells are your contacts.

1283
00:59:15,930 --> 00:59:21,400
For PC1D, you can only feed it
shunt resistances and series

1284
00:59:21,400 --> 00:59:24,690
resistances, which is nice
in that it's convenient.

1285
00:59:24,690 --> 00:59:28,030
But if you don't know them
or if you can't measure them

1286
00:59:28,030 --> 00:59:29,540
because you don't
have the cells,

1287
00:59:29,540 --> 00:59:31,380
then that's a hindering factor.

1288
00:59:31,380 --> 00:59:33,460
So therefore, it's nice
to be able to model

1289
00:59:33,460 --> 00:59:36,670
the physics of your contacts
by taking the barrier

1290
00:59:36,670 --> 00:59:39,040
height of your metal
and semiconductor,

1291
00:59:39,040 --> 00:59:41,650
and by looking at the
recombination velocity.

1292
00:59:41,650 --> 00:59:44,900
So both SCAPS and
AMPS allows for that.

1293
00:59:44,900 --> 00:59:47,610
And at the same time, SCAPS
also allows for modeling

1294
00:59:47,610 --> 00:59:51,441
with your shunt resistance
and series resistance.

1295
00:59:51,441 --> 00:59:53,690
So that's nice in that if
you have those measurements,

1296
00:59:53,690 --> 00:59:56,040
you can just do that
instead of mucking around

1297
00:59:56,040 --> 00:59:58,770
with the physics.

1298
00:59:58,770 --> 01:00:01,770
So other considerations include
the total number of flares

1299
01:00:01,770 --> 01:00:03,630
that you can simulate.

1300
01:00:03,630 --> 01:00:05,780
AMPS is actually,
has an advantage

1301
01:00:05,780 --> 01:00:08,340
in that you can simulate
up to 30 layers.

1302
01:00:08,340 --> 01:00:10,640
So if you have graded
materials, it's

1303
01:00:10,640 --> 01:00:14,250
a good approximation to be able
to just simulate 30 layers.

1304
01:00:14,250 --> 01:00:17,440
They all pretty much do same
basic set of simulations,

1305
01:00:17,440 --> 01:00:20,220
including simulating
under dark conditions,

1306
01:00:20,220 --> 01:00:25,110
under illuminated conditions,
and band calculations.

1307
01:00:25,110 --> 01:00:30,510
SCAPS, and at PC1D also allow
for additional measurements,

1308
01:00:30,510 --> 01:00:32,980
like capacitance measurements
as a function of frequency,

1309
01:00:32,980 --> 01:00:35,630
or as a function of voltage,
which is very nice for physics.

1310
01:00:38,180 --> 01:00:42,330
Other considerations include
documentation and ease of use.

1311
01:00:42,330 --> 01:00:44,350
AMPS probably had the
best documentation.

1312
01:00:44,350 --> 01:00:46,790
You had an 80-page user manual.

1313
01:00:46,790 --> 01:00:49,720
SCAPS was this composed of
random PowerPoint slides

1314
01:00:49,720 --> 01:00:51,360
that were thrown on the website.

1315
01:00:51,360 --> 01:00:53,920
So it's a little bit
harder to figure out.

1316
01:00:53,920 --> 01:00:55,795
And finally, in
terms of ease of use,

1317
01:00:55,795 --> 01:00:59,640
I'd say PC1D is the easiest
just because you don't really

1318
01:00:59,640 --> 01:01:00,740
delve into the physics.

1319
01:01:00,740 --> 01:01:02,870
You just type in values.

1320
01:01:02,870 --> 01:01:04,040
And it simulates.

1321
01:01:04,040 --> 01:01:07,630
Whereas, with AMPS and SCAPS, if
you get your parameters wrong,

1322
01:01:07,630 --> 01:01:12,160
it won't simulate, or it'll
freeze, or things like that.

1323
01:01:12,160 --> 01:01:16,180
So here's this brief
run through of the user,

1324
01:01:16,180 --> 01:01:18,670
of the interface for SCAPS.

1325
01:01:18,670 --> 01:01:22,590
So this is the main page
where you set your measurement

1326
01:01:22,590 --> 01:01:26,590
parameters like your lighting
conditions, your voltages.

1327
01:01:26,590 --> 01:01:28,850
And then, from there, you
can define the structure

1328
01:01:28,850 --> 01:01:29,830
that you're simulating.

1329
01:01:29,830 --> 01:01:32,620
So in this case, this is for
a p-i-n amorphous silicon

1330
01:01:32,620 --> 01:01:34,056
structure.

1331
01:01:34,056 --> 01:01:35,680
And then, you can
define the properties

1332
01:01:35,680 --> 01:01:37,150
for each of those layers.

1333
01:01:37,150 --> 01:01:38,890
So this, for example,
are the properties

1334
01:01:38,890 --> 01:01:40,170
for the p-type layer.

1335
01:01:40,170 --> 01:01:42,090
So these are basic
material properties

1336
01:01:42,090 --> 01:01:45,070
like your electron
mobility, your band gaps,

1337
01:01:45,070 --> 01:01:46,150
so on, so forth.

1338
01:01:46,150 --> 01:01:49,790
And on the left, you
can define your traps.

1339
01:01:49,790 --> 01:01:51,810
As for AMPS, it's
got a little bit more

1340
01:01:51,810 --> 01:01:56,650
of a minimalistic layout, which
is more pleasing to the eye.

1341
01:01:56,650 --> 01:01:58,905
So this is like your basic page.

1342
01:01:58,905 --> 01:02:01,540
And then, from there, if you
can define each of your layers.

1343
01:02:05,400 --> 01:02:07,818
So with that, I'll
pass it on to Naomi.

1344
01:02:18,480 --> 01:02:21,170
NAOMI: So for six
organic materials and six

1345
01:02:21,170 --> 01:02:24,660
inorganic materials, we found
all their physical properties

1346
01:02:24,660 --> 01:02:25,760
from literature.

1347
01:02:25,760 --> 01:02:28,330
So we use either
well-known properties,

1348
01:02:28,330 --> 01:02:31,240
or the most common properties
for these materials

1349
01:02:31,240 --> 01:02:33,240
for the most common
crystalline structure,

1350
01:02:33,240 --> 01:02:37,440
or the crystallinity that we
would use for solar cells. .

1351
01:02:37,440 --> 01:02:39,300
And for some
materials, it was very

1352
01:02:39,300 --> 01:02:42,550
hard to find certain properties,
such as the density of states,

1353
01:02:42,550 --> 01:02:43,330
for example.

1354
01:02:43,330 --> 01:02:46,860
And we had to approximate
these numbers.

1355
01:02:46,860 --> 01:02:48,620
And then, we used
these properties,

1356
01:02:48,620 --> 01:02:52,770
these basic properties to
compare the performance

1357
01:02:52,770 --> 01:02:54,600
from literature
versus the values

1358
01:02:54,600 --> 01:02:57,840
that we obtained
from AMPS and SCAPS.

1359
01:02:57,840 --> 01:03:00,150
So for inorganic
solar cells, we can

1360
01:03:00,150 --> 01:03:03,200
see that there's a
good correspondence

1361
01:03:03,200 --> 01:03:07,010
between literature values
and both simulation tools.

1362
01:03:07,010 --> 01:03:08,840
And this is likely
due to the fact

1363
01:03:08,840 --> 01:03:11,920
that inorganic materials
have more similar properties

1364
01:03:11,920 --> 01:03:14,610
to silicon than
organic materials.

1365
01:03:14,610 --> 01:03:17,110
And the simulation tools
were based on silicon

1366
01:03:17,110 --> 01:03:18,560
when they were created.

1367
01:03:18,560 --> 01:03:22,200
So we looked at the open-circuit
voltage, short-circuit current,

1368
01:03:22,200 --> 01:03:25,980
the fill factor, and the
power conversion efficiency.

1369
01:03:25,980 --> 01:03:29,020
But then, when we had an
organic component to the device,

1370
01:03:29,020 --> 01:03:32,030
we see that there are more
significant discrepancies

1371
01:03:32,030 --> 01:03:35,110
between literature values
and the simulations.

1372
01:03:35,110 --> 01:03:38,730
So for example, in this case,
we had usually an overestimation

1373
01:03:38,730 --> 01:03:42,330
of the performance with
SCAPS and an underestimation

1374
01:03:42,330 --> 01:03:43,910
with AMPS.

1375
01:03:43,910 --> 01:03:46,140
And we also have
to note that we're

1376
01:03:46,140 --> 01:03:49,000
expecting lower performance
from our simulations

1377
01:03:49,000 --> 01:03:49,930
than the literature.

1378
01:03:49,930 --> 01:03:52,170
Because usually in
literature, the values

1379
01:03:52,170 --> 01:03:54,450
are reported for
bulk heterojunctions.

1380
01:03:54,450 --> 01:03:56,090
So a mixture of
the two materials

1381
01:03:56,090 --> 01:03:58,810
while in the simulation,
we use only flat bilayer

1382
01:03:58,810 --> 01:04:00,790
heterojunctions.

1383
01:04:00,790 --> 01:04:05,180
So here we can see that we have
been very little fill factors

1384
01:04:05,180 --> 01:04:08,970
for SCAPS and very
high efficiencies.

1385
01:04:08,970 --> 01:04:11,040
So that's the main discrepancy.

1386
01:04:11,040 --> 01:04:13,570
And for organic
solar cells, we also

1387
01:04:13,570 --> 01:04:17,020
obtained a very high
efficiencies from SCAP

1388
01:04:17,020 --> 01:04:21,760
as well as open-circuit voltage,
and some very significant

1389
01:04:21,760 --> 01:04:25,060
underestimations from AMPS,
of the short-circuit current,

1390
01:04:25,060 --> 01:04:26,900
and the efficiency.

1391
01:04:26,900 --> 01:04:29,260
But due to the
[INAUDIBLE] use of SCAP,

1392
01:04:29,260 --> 01:04:31,270
AMPS was taking longer to run.

1393
01:04:31,270 --> 01:04:33,970
And it was more sensitive to
small changes in property.

1394
01:04:33,970 --> 01:04:36,400
Sometimes we would have
convergence failures.

1395
01:04:36,400 --> 01:04:39,130
So we decided to
look mostly at SCAPS.

1396
01:04:39,130 --> 01:04:41,640
And we varied some
parameter properties

1397
01:04:41,640 --> 01:04:43,420
to look at how these
softwares would

1398
01:04:43,420 --> 01:04:46,361
respond to changes in
the physical properties

1399
01:04:46,361 --> 01:04:46,860
[INAUDIBLE].

1400
01:04:51,140 --> 01:04:58,440
STUDENT 4: So this is a where
the detailed study comes.

1401
01:04:58,440 --> 01:05:00,050
And the first thing
we have looked at

1402
01:05:00,050 --> 01:05:02,650
is the temperature [INAUDIBLE].

1403
01:05:02,650 --> 01:05:05,790
So only a representative
figure is shown here.

1404
01:05:05,790 --> 01:05:09,140
So as you learned in the class,
if we increase the temperature

1405
01:05:09,140 --> 01:05:14,570
from 250 to 350, the efficiency
and open-circuit voltage

1406
01:05:14,570 --> 01:05:15,760
is the equation.

1407
01:05:15,760 --> 01:05:21,510
And this is kind of
expected, because decreasing.

1408
01:05:21,510 --> 01:05:27,360
So we can explain the reduction
of open-circuit voltage

1409
01:05:27,360 --> 01:05:31,060
by, yeah, so if we
increase the temperature,

1410
01:05:31,060 --> 01:05:35,920
the electrons gets easier to
excite to the conduction band.

1411
01:05:35,920 --> 01:05:39,160
So that effective band gap
is actually decreasing.

1412
01:05:39,160 --> 01:05:41,680
And also we didn't show the
short-circuit current data

1413
01:05:41,680 --> 01:05:42,180
here.

1414
01:05:42,180 --> 01:05:45,502
But there's a slight increase
of short-circuit current.

1415
01:05:45,502 --> 01:05:47,710
And this could be, also,
explained by the same thing,

1416
01:05:47,710 --> 01:05:51,840
like it's easier to get
excited to the conduction band.

1417
01:05:51,840 --> 01:05:54,790
And the second thing we have
looked at is layer thickness.

1418
01:05:54,790 --> 01:05:58,740
And also, here, there only
a representative figure

1419
01:05:58,740 --> 01:06:00,010
is showing here.

1420
01:06:00,010 --> 01:06:03,840
So if we increase the
thickness from 0 to 1,000

1421
01:06:03,840 --> 01:06:06,610
for the [INAUDIBLE],
the efficiency

1422
01:06:06,610 --> 01:06:09,330
and the short-circuit current
is initially going up.

1423
01:06:09,330 --> 01:06:13,140
And after certain point,
the efficiency, [INAUDIBLE],

1424
01:06:13,140 --> 01:06:14,550
is slowly going down.

1425
01:06:14,550 --> 01:06:16,150
And this is also expected.

1426
01:06:16,150 --> 01:06:21,840
Because for the
observing material,

1427
01:06:21,840 --> 01:06:27,540
when we first initially
increased the layer thickness,

1428
01:06:27,540 --> 01:06:30,230
it gets more,
initially more light.

1429
01:06:30,230 --> 01:06:33,280
But after certain point,
absorbing more light effect

1430
01:06:33,280 --> 01:06:34,360
is already saturated.

1431
01:06:34,360 --> 01:06:38,110
So increased layer thickness
just means the more distance

1432
01:06:38,110 --> 01:06:39,360
to the electrodes.

1433
01:06:39,360 --> 01:06:42,950
However, whereas for
the acceptor material,

1434
01:06:42,950 --> 01:06:46,710
there's no significant of
effect of the layer thickness

1435
01:06:46,710 --> 01:06:49,272
on the performances.

1436
01:06:49,272 --> 01:06:51,730
AUDIENCE: It's like will you
help me with this graph, which

1437
01:06:51,730 --> 01:06:52,253
ones are--

1438
01:06:52,253 --> 01:06:53,086
STUDENT 1: Question?

1439
01:06:53,086 --> 01:06:55,300
AUDIENCE: Are the dotted
lines the current?

1440
01:06:55,300 --> 01:06:58,025
STUDENT 1: Yeah, so the
solid line is efficiency.

1441
01:06:58,025 --> 01:07:02,516
And the dashed line is current.

1442
01:07:02,516 --> 01:07:04,996
AUDIENCE: And one is for
SCAPS and one is for AMPS?

1443
01:07:04,996 --> 01:07:07,500
STUDENT 4: No, All
the simulations

1444
01:07:07,500 --> 01:07:11,140
done in SCAPS actually.

1445
01:07:11,140 --> 01:07:13,767
STUDENT 5: So I'm going to
talk about how you change

1446
01:07:13,767 --> 01:07:15,850
your particle size, you
will change your band gap,

1447
01:07:15,850 --> 01:07:18,420
and also change your
result of the simulation.

1448
01:07:18,420 --> 01:07:21,470
So as you know, changing
your particle size

1449
01:07:21,470 --> 01:07:24,740
of the [INAUDIBLE] will change
the band gap of the material.

1450
01:07:24,740 --> 01:07:29,280
And this is very important
for organic solar cell.

1451
01:07:29,280 --> 01:07:31,390
From the table
above, you can see

1452
01:07:31,390 --> 01:07:34,520
when we change the lead
sulfide, lead sulfide particle

1453
01:07:34,520 --> 01:07:37,800
size from bulk material
to 2.4 nanometer,

1454
01:07:37,800 --> 01:07:43,170
you can change your band gap
from 0.4 increase to 2.1.

1455
01:07:43,170 --> 01:07:47,290
So we will use these numbers
into the simulation tools

1456
01:07:47,290 --> 01:07:50,990
to simulate the
efficiency of two system.

1457
01:07:50,990 --> 01:07:52,820
One is lead sulfide zinc oxide.

1458
01:07:52,820 --> 01:07:56,040
The other one is lead
sulfide titanium.

1459
01:07:56,040 --> 01:07:59,950
So you can see the white
dot on the figures.

1460
01:07:59,950 --> 01:08:01,520
That's mean efficiency.

1461
01:08:01,520 --> 01:08:07,410
The highest efficiency occur
at the band gap is around 1.5.

1462
01:08:07,410 --> 01:08:09,850
So that's mean the
particle size is

1463
01:08:09,850 --> 01:08:12,210
smaller than the bulk material.

1464
01:08:12,210 --> 01:08:14,250
So which just mean if
you use smaller particle

1465
01:08:14,250 --> 01:08:17,560
size with the
higher band gap, you

1466
01:08:17,560 --> 01:08:20,490
can get a higher efficiency
because two reasons.

1467
01:08:20,490 --> 01:08:23,160
The first is your [INAUDIBLE]
increased because your band

1468
01:08:23,160 --> 01:08:24,240
gap increased.

1469
01:08:24,240 --> 01:08:27,029
And the second is that
your [? fill ?] factor also

1470
01:08:27,029 --> 01:08:30,500
increased in both systems.

1471
01:08:30,500 --> 01:08:35,430
So how is this simulation
[INAUDIBLE] of this simulation

1472
01:08:35,430 --> 01:08:36,950
compared to the literature?

1473
01:08:36,950 --> 01:08:39,630
So we choose the lead
sulfide titanium system.

1474
01:08:39,630 --> 01:08:44,340
So we used the structure in
the right, above figures.

1475
01:08:44,340 --> 01:08:46,710
Now, there's titanium
lead sulfide.

1476
01:08:46,710 --> 01:08:49,590
And then, the
[INAUDIBLE] is gold.

1477
01:08:49,590 --> 01:08:52,819
And then, the world record
efficiency, right now,

1478
01:08:52,819 --> 01:08:54,819
is around 5.1%.

1479
01:08:54,819 --> 01:08:57,434
So the particle size
of this literature used

1480
01:08:57,434 --> 01:09:00,250
is five nanometer.

1481
01:09:00,250 --> 01:09:03,189
So find the nanometer
in our simulation.

1482
01:09:03,189 --> 01:09:06,550
The result is around
4% to 5%, which is,

1483
01:09:06,550 --> 01:09:08,470
it's very close to each other.

1484
01:09:08,470 --> 01:09:11,950
But our simulation result
can help the future direction

1485
01:09:11,950 --> 01:09:14,740
of this research regime.

1486
01:09:14,740 --> 01:09:16,700
Because you can see
the simulation result.

1487
01:09:16,700 --> 01:09:20,500
If you change the particle
size to the lower,

1488
01:09:20,500 --> 01:09:24,010
to the smaller particle, you can
increase the efficiency to 8%.

1489
01:09:24,010 --> 01:09:27,729
So that's how simulation
can helps the research.

1490
01:09:27,729 --> 01:09:31,431
So I would just pass to
the sensitivity part.

1491
01:09:38,620 --> 01:09:42,710
STUDENT 6: We also to determine
the critical parameters

1492
01:09:42,710 --> 01:09:46,870
to which [INAUDIBLE] that
the performance [INAUDIBLE]

1493
01:09:46,870 --> 01:09:51,090
we calculated sensitivity.

1494
01:09:51,090 --> 01:09:57,890
Sensitivities are calculated
from changes in efficiency,

1495
01:09:57,890 --> 01:10:03,700
[INAUDIBLE] by varying
parameters, simulation

1496
01:10:03,700 --> 01:10:06,950
parameters, or
material properties.

1497
01:10:06,950 --> 01:10:11,205
They were expressed
in terms of change,

1498
01:10:11,205 --> 01:10:18,080
a 1% change of efficiency in the
parameter of relative to basis

1499
01:10:18,080 --> 01:10:19,050
value.

1500
01:10:19,050 --> 01:10:23,540
So as we can say, we found
four major parameters.

1501
01:10:23,540 --> 01:10:25,500
And the [INAUDIBLE]
two things out,

1502
01:10:25,500 --> 01:10:28,480
there were no band gaps
and electron affinity,

1503
01:10:28,480 --> 01:10:31,450
which are well-known
material properties.

1504
01:10:31,450 --> 01:10:34,990
And others are [INAUDIBLE]
thickness and temperature,

1505
01:10:34,990 --> 01:10:40,030
which can be controlled the
[? web ?] by it's [INAUDIBLE].

1506
01:10:40,030 --> 01:10:43,160
So from this
sensitivity [INAUDIBLE],

1507
01:10:43,160 --> 01:10:47,110
we strength, I mean,
confidence of our simulations.

1508
01:10:56,840 --> 01:10:59,650
NAOMI: So to conclude, after
doing all these simulations,

1509
01:10:59,650 --> 01:11:02,260
we found that the these
simulation softwares

1510
01:11:02,260 --> 01:11:06,340
were useful tools to simulate
efficiency trends as opposed

1511
01:11:06,340 --> 01:11:08,190
to absolute values
of the performance

1512
01:11:08,190 --> 01:11:11,360
parameters, which remain
challenging to simulate,

1513
01:11:11,360 --> 01:11:14,130
especially for
organic compounds.

1514
01:11:14,130 --> 01:11:16,940
However, the
sensitivity analysis

1515
01:11:16,940 --> 01:11:20,420
was good to validate that
the most well-known material

1516
01:11:20,420 --> 01:11:22,740
properties seem to
have the highest

1517
01:11:22,740 --> 01:11:24,350
influence on the efficiency.

1518
01:11:24,350 --> 01:11:27,440
And we can usually also
control temperature and layer

1519
01:11:27,440 --> 01:11:29,580
thickness, which
we're also very, very

1520
01:11:29,580 --> 01:11:33,220
influent for the efficiency.

1521
01:11:33,220 --> 01:11:35,820
So this project was
useful to collect

1522
01:11:35,820 --> 01:11:37,670
a lot of material properties.

1523
01:11:37,670 --> 01:11:39,620
And we could potentially
create a database

1524
01:11:39,620 --> 01:11:43,350
of properties that could be
useful for solar research.

1525
01:11:43,350 --> 01:11:45,170
And this could be
included in such,

1526
01:11:45,170 --> 01:11:48,260
in a project such as the
Materials Project, which

1527
01:11:48,260 --> 01:11:50,860
incorporates lots of
databases about materials

1528
01:11:50,860 --> 01:11:52,410
for different applications.

1529
01:11:52,410 --> 01:11:55,200
And then, if you could connect
these material databases

1530
01:11:55,200 --> 01:11:57,020
to the simulation
tools directly,

1531
01:11:57,020 --> 01:12:00,020
it would be good for a
user who simply wants

1532
01:12:00,020 --> 01:12:02,330
to input a pair of materials.

1533
01:12:02,330 --> 01:12:05,070
And then, we could
get the output

1534
01:12:05,070 --> 01:12:07,780
as performance
parameters directly.

1535
01:12:07,780 --> 01:12:11,470
And finally, we want to thank
Professor Buonassisi, as well

1536
01:12:11,470 --> 01:12:13,970
as the research groups
from Gent University

1537
01:12:13,970 --> 01:12:16,810
and from Pennsylvania State
University for the use

1538
01:12:16,810 --> 01:12:20,642
of their simulations softwares.

1539
01:12:20,642 --> 01:12:22,130
[APPLAUSE]

1540
01:12:29,602 --> 01:12:31,102
AUDIENCE: You said
you had a problem

1541
01:12:31,102 --> 01:12:33,746
modeling the bulk
heterojunction organics?

1542
01:12:33,746 --> 01:12:35,749
I mean, because it's bulk
heterojunction instead

1543
01:12:35,749 --> 01:12:36,290
of a bilayer.

1544
01:12:36,290 --> 01:12:38,750
Did you try just
modeling a single layer

1545
01:12:38,750 --> 01:12:42,806
with the properties that
are a mixture of materials?

1546
01:12:42,806 --> 01:12:43,780
NAOMI: So.

1547
01:12:43,780 --> 01:12:52,400
STUDENT 1: Yeah, so actually, we
tried to do bulk heterojunction

1548
01:12:52,400 --> 01:12:53,620
modeling as well.

1549
01:12:53,620 --> 01:12:57,620
But it is limited by the
simulation capabilities.

1550
01:12:57,620 --> 01:13:01,426
So we can define the layer.

1551
01:13:01,426 --> 01:13:04,910
Yeah, so you can define
several layers in here.

1552
01:13:04,910 --> 01:13:08,817
But we--

1553
01:13:08,817 --> 01:13:10,650
STUDENT 4: We can show
the software to them.

1554
01:13:10,650 --> 01:13:12,830
STUDENT 1: Uh-huh.

1555
01:13:12,830 --> 01:13:17,310
So if we want to do the
bulk heterojunction,

1556
01:13:17,310 --> 01:13:21,900
we could do, just put one layer
where the effected material

1557
01:13:21,900 --> 01:13:22,826
properties.

1558
01:13:22,826 --> 01:13:26,330
However, the hard
thing was, the shifts

1559
01:13:26,330 --> 01:13:29,840
at the band gap,
actually, the parameter.

1560
01:13:29,840 --> 01:13:32,220
However, you could not
define the band gap.

1561
01:13:32,220 --> 01:13:35,170
Because even if we
did just one layer,

1562
01:13:35,170 --> 01:13:37,220
it is a mixture of
two different layers.

1563
01:13:37,220 --> 01:13:38,690
So it's hard to
define band gaps.

1564
01:13:38,690 --> 01:13:40,546
So it will mess up everything.

1565
01:13:40,546 --> 01:13:41,474
So we couldn't.

1566
01:13:44,730 --> 01:13:46,310
AUDIENCE: Your
last slide made me

1567
01:13:46,310 --> 01:13:51,270
think of some recent publicity
from a group, Harvard, I think.

1568
01:13:51,270 --> 01:13:55,970
Some guy trying to use
the distributed computing

1569
01:13:55,970 --> 01:13:59,200
idea similar Folding@home
or [? Study at Home, ?]

1570
01:13:59,200 --> 01:14:01,560
wants people to download
his screensaver,

1571
01:14:01,560 --> 01:14:05,450
and screen thousands of
different organic materials,

1572
01:14:05,450 --> 01:14:07,480
I think, for photovoltaics.

1573
01:14:07,480 --> 01:14:07,980
NAOMI: Yeah.

1574
01:14:07,980 --> 01:14:11,695
AUDIENCE: Do You know what
software they used for that?

1575
01:14:14,158 --> 01:14:14,908
NAOMI: Don't know.

1576
01:14:14,908 --> 01:14:15,396
AUDIENCE: Custom software.

1577
01:14:15,396 --> 01:14:16,372
AUDIENCE: Custom software?

1578
01:14:16,372 --> 01:14:16,872
OK.

1579
01:14:20,770 --> 01:14:24,427
So can you guys go back to the,
you had an array of bar charts,

1580
01:14:24,427 --> 01:14:26,010
at some point, when
you were comparing

1581
01:14:26,010 --> 01:14:28,460
the different simulation tools.