Nanotechnology for Next Generation
Solar Cells
Group 1:
Amy Cornforth, Tony Grupp, Ana
D’Almeida
February 5, 2010
Presentation Overview
1.
2.
3.
4.
Solar cell introduction
Quantum dot solar cells
Dye-sensitized solar cells (DSSC)
Hybrid organic solar cells
Solar Cells
• Units that have the ability of converting sunlight
into electricity
• Made of semiconducting material
• Can be used for varied purposes, e.g. to power
watches, to light houses, and to provide power
to the electrical grids
Image found at: http://en.wikipedia.org/wiki/File:Borealis3windmills.jpg
How Solar Cells Work. http://solarpanelworld.com/how-solar-cells-work.php
Solar Cells
• How do they work?
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Light is absorbed by semiconductor
Energy of the electrons increases
Electrons move in the material
Charge carriers have to be present
• Limitations
– Band gap of the semi-conducting material
– Maximum efficiency of a solar cell (single
material) is about 30 %
How Solar Cells Work. http://solarpanelworld.com/how-solar-cells-work.php
Solar Cell Development
Three Generations of solar cell technology:
1. Single-crystal silicon based photovoltaic devices
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Good efficiency
High Cost
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Higher than traditionally-produced electricity
2. CuInGaSe2 (CIGS) polycrystalline semiconductor
thin films
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Low Cost
Less Efficiency
3. Nanotechnology-enhanced solar cells
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Low Cost
Medium Efficiency
Quantum Dots
Advantages
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Adjustable band-gap
Moldable
Facilitate collection and transport of carriers
Increase efficiency of solar cells
• by extending the band gap of solar cells
• by generating more charges from a single photon
Quantum Dots and Ultra-Efficient Solar Cells? http://www.i-sis.org.uk/QDAUESC.php
Quantum Dots
• Quantum dot sensitized solar cells
(QDSCs) are third-generation
photovoltaic devices
• Semiconductor sensitizers
– Very tunable
– Theoretically increase
efficiency of solar cells up to
44%
Image found at::
http://nanopatentsandinnovations.blogspot.com/2009_11_01_archive.
html
Published in:Ivn Mora-Ser, Sixto Gimnez, Francisco Fabregat-Santiago, Roberto Gmez, Qing Shen, Taro Toyoda, Juan Bisquert;Recombination in
Quantum Dot Sensitized Solar Cells.Accounts of Chemical Research 2009 42 (11), DOI: 10.1021/ar900134d , Copyright © 2009 ASC
Quantum Dots
• How to improve the performance and stability of
QDSCs?
•
Deposit CdSe quantum dots on nanostructured
mesoporous TiO2 electrodes
Image found at: www.mrl.ucsb.edu/.../RISE/interns01/AlysonW.html
Published in:Ivn Mora-Ser, Sixto Gimnez, Francisco Fabregat-Santiago, Roberto Gmez, Qing Shen, Taro Toyoda, Juan Bisquert;Recombination in
Quantum Dot Sensitized Solar Cells.Accounts of Chemical Research 2009 42 (11), DOI: 10.1021/ar900134d , Copyright © 2009 ASC
Dye-Sensitized Solar Cells
Published in: Hiroshi Imahori and Tomokazu Umeyama; J. Phys. Chem. C 2009, 113 (21).
DOI: 10.1021/jp9007448
Copyright © 2009 American Chemical Society
DSSC Basics
• Thin-film solar cell
– Think sandwich
• Electrons for movement are provided by the
photosensitive dye
– Electrons provided by silicon base in other cells
– Compare with previously demonstrated cell
• Nanomaterials used to create 3-D structure for
dye
– Greater number of dye molecules due to greater
internal surface area
Basic DSSC Layers:
1. Glass coated with
fluorine-doped tin
oxide
2. Titanium dioxide
layer (n-type
semiconductor)
3. Ruthenium dye
4. Electrolyte
solution
5. Glass coated with
platinum
Image found at http://en.wikipedia.org/wiki/Dye-sensitized_solar_cell, cited Secondary Article 2
a) Demonstration of DSSC cell
b) TiO Nanostructure
c) Electron energy levels
1. Electron injection from dye to conduction band
2. Electron recombination with dye cation
3. Dye regeneration from electrolyte
4. Electron recombination with electrolyte
5. Electron trapping in nanostructure
Published in: Qifeng Zhang, Christopher S. Dandeneau, Xiaoyuan Zhou, and Guozhong Cao; Advanced Materials. 2009, 21,
4087–4108. DOI: 10.1002/adma.200803827 Copyright © 2009 Wiley-VCH
DSSC Nanostructure
• Porous interconnected structure
• Surface area increased 1000 times
when compared to bulk materials
• Crystals cause light-scattering and
increase efficiency, but also cause
electron trapping
• Thickness, shape, material all effect cell
efficiency
Published in: Qifeng Zhang, Christopher S. Dandeneau, Xiaoyuan Zhou, and Guozhong Cao; Advanced Materials. 2009, 21,
4087–4108. DOI: 10.1002/adma.200803827 Copyright © 2009 Wiley-VCH
ZnO Nanostructures
Published in: Qifeng Zhang, Christopher S. Dandeneau, Xiaoyuan Zhou, and Guozhong Cao; Advanced Materials. 2009, 21,
4087–4108. DOI: 10.1002/adma.200803827 Copyright © 2009 Wiley-VCH
a) Diagram of cell with nanowires
b) Image of nanowires
c) Comparison of cell performance for various shapes
and types of nanostructures
Published in: Qifeng Zhang, Christopher S. Dandeneau, Xiaoyuan Zhou, and Guozhong Cao; Advanced Materials. 2009, 21,
4087–4108. DOI: 10.1002/adma.200803827 Copyright © 2009 Wiley-VCH
DSSC Modifications
• Replace organic electrolyte solution
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Volatile, undergoes expansion and contraction
Gel electrolyte
Polymer electrolyte
Solid organic conductor
Inorganic semiconductor
• Replace ruthenium dye
– Difficult to produce, environmentally dangerous
– Organic dyes
– Inorganic quantum dots
• Replace TiO2 layer
– SnO2
– ZnO
Published in: L. M. Peter; J. Phys. Chem. C 2007, 111 (18). DOI: 10.1021/jp069058b
Copyright © 2007 American Chemical Society
DSSC Development History
• 1991
– Nature paper by O'Regan and Grätzel
– First suggestion of workable DSSC
• 2006
– Use of nanowires and nanoparticles
– Demonstrated good chemical and thermal
resistance
• 2007, 2008
– Use of low-cost organic dyes and solvent-free
electrolyte solution investigated
Dye-Sensitized Solar Cell. Wikipedia. http://en.wikipedia.org/wiki/Dye-sensitized_solar_cell
DSSC Efficiency
• High chance of proton absorption and
high chance of electron movement
– 90% Quantum Efficiency for green light
• Quantum Efficiency-chance that one photon will
convert one electron
• Overall efficiency is 11% or less,
depending on materials of construction
Dye-Sensitized Solar Cell. Wikipedia. http://en.wikipedia.org/wiki/Dye-sensitized_solar_cell
DSSC Summary
• Medium efficiency
• Low cost
• Problems to be addressed:
– Liquid electrolyte (freezing, expanding,
volatility)
– Poor performance in red region of light
Dye-Sensitized Solar Cell. Wikipedia. http://en.wikipedia.org/wiki/Dye-sensitized_solar_cell
Organic Hybrid Solar Cells
• PT (polythiophene) and other oligomers have better
morphology and optoelectronic properties for
increased efficiency
• Based on P3HT (poly-3(hexylthiophene)) derivatives
Image at http://www.iae.kyoto-u.ac.jp/molecule/nedo-mirai.jpg
What is an Oligothiophene?
• Definition: Molecules in which two or more thiophene
rings are linked together
• Gives rise to many optical and electrical properties
such as fluorescence, semiconductance, and light
emission
Both images found at http://www.isof.cnr.it/ppage/capob/thiof.html
Scheme 1: Mechanism of Excited State Deactivation of
Higher Generation Thiophene Dendrimers
Published in: Guda Ramakrishna; Ajit Bhaskar; Peter Bauerle; Theodore Goodson; J. Phys. Chem. A 2008, 112, 2018-2026.
DOI: 10.1021/jp076048h Copyright © 2008 American Chemical Society
Why are oligothiophenes important?
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Highly versatile chemistry
Very simple to synthesize basic molecules
Used in organic light emitting diodes (LEDs)
Field effect transistors
– Uses an electric current to control the conductivity
of charge
• Organic photovoltaic and light harvesting devices
(solar cells)
P3HT – poly(3-hexylthiophene)
• One of the major layers in an organic solar cell to
increase efficiency
• In some lower quality solar cells the addition of P3HT
increased efficiency from 0.05% up to 0.29%
• The best organic solar cells can reach up to 4-5%
efficiency
• Current commercial solar cells use highly purified
silicon and reach 22% efficiency
PT and P3HT
• A) PT
• B) P3HT
• Both are derived from the
basic oligothiophene
structure
• P3HT has a hexane chain
added to the C5 position
of each thiophene ring
Image found at http://www.condensed-matter.uni-tuebingen.de/resources/pictures/molecules/P3HT.gif
Figure 1 Molecular structures of the investigated 3D
oligothiophene dendrimers.
Published in: Guda Ramakrishna; Ajit Bhaskar; Peter Bauerle; Theodore Goodson; J. Phys. Chem. A 2008, 112, 2018-2026.
DOI: 10.1021/jp076048h Copyright © 2008 American Chemical Society
Atomic structure in the case of (a) P3HT
with 2510 atoms and (b) P3HT with
10 040 atoms. Hydrogen atoms have
been removed for clarity. Main chains
are shown in black and side chains in
gray.
Published in: Nenad Vukmirović; Lin-Wang Wang; J. Phys. Chem. B 2009, 113, 409-415. DOI: 10.1021/jp808360y
Copyright © 2008 American Chemical Society
What is needed?
• Organic solar cells have two main objectives:
– 1. They must have efficient excitation
delocalization and energy transfer to best mimic
natural systems (such as plants)
– 2. Must be able to convert solar energy and have
large electron mobility properties (P3HT helps
considerably with this)
Published in: McGehee, M.; Mayer, A.; Parmer, J.; Rowell, M.; Topinka, M.; Burkhardt, G. Improving Organic Solar
Cells C 2007 Stanford University
Zinc and Titanium Oxide Nanorods
• Simple solar cell design where zinc oxide nanorods
are grown and a layer of titanium oxide is layered on
those rods
• P3HT is layered overtop the rods as the holeconducting polymer
• Significantly increases the voltage difference across
the cell, and can be exposed to atmospheric air to
increase efficiency
Published in: McGehee, M.; Mayer, A.; Parmer, J.; Rowell, M.; Topinka, M.; Burkhardt, G. Improving Organic Solar
Cells C 2007 Stanford University
How can we improve?
• One field of current research is to form a mesh of
carbon nanotubes with a P3HT light absorbing film
• The following slides show one experiment from
Stanford University with the current and voltage
across a solar cell
Published in: McGehee, M.; Mayer, A.; Parmer, J.; Rowell, M.; Topinka, M.; Burkhardt, G. Improving Organic Solar
Cells C 2007 Stanford University
Published in: McGehee, M.; Mayer, A.; Parmer, J.; Rowell, M.; Topinka, M.; Burkhardt, G. Improving Organic Solar
Cells C 2007 Stanford University
Published in: McGehee, M.; Mayer, A.; Parmer, J.; Rowell, M.; Topinka, M.; Burkhardt, G. Improving Organic Solar
Cells C 2007 Stanford University
Published in: McGehee, M.; Mayer, A.; Parmer, J.; Rowell, M.; Topinka, M.; Burkhardt, G. Improving Organic Solar
Cells C 2007 Stanford University
Published in: McGehee, M.; Mayer, A.; Parmer, J.; Rowell, M.; Topinka, M.; Burkhardt, G. Improving Organic Solar
Cells C 2007 Stanford University
Published in: McGehee, M.; Mayer, A.; Parmer, J.; Rowell, M.; Topinka, M.; Burkhardt, G. Improving Organic Solar
Cells C 2007 Stanford University
Published in: McGehee, M.; Mayer, A.; Parmer, J.; Rowell, M.; Topinka, M.; Burkhardt, G. Improving Organic Solar
Cells C 2007 Stanford University
Published in: McGehee, M.; Mayer, A.; Parmer, J.; Rowell, M.; Topinka, M.; Burkhardt, G. Improving Organic Solar
Cells C 2007 Stanford University
Published in: McGehee, M.; Mayer, A.; Parmer, J.; Rowell, M.; Topinka, M.; Burkhardt, G. Improving Organic Solar
Cells C 2007 Stanford University
Published in: McGehee, M.; Mayer, A.; Parmer, J.; Rowell, M.; Topinka, M.; Burkhardt, G. Improving Organic Solar
Cells C 2007 Stanford University
Published in: McGehee, M.; Mayer, A.; Parmer, J.; Rowell, M.; Topinka, M.; Burkhardt, G. Improving Organic Solar
Cells C 2007 Stanford University
Results
• Efficiency over the system was nearly triple from
previous experiments, going up to 3% using a 95%
transparent film over the top of the cell
• An increase in the carbon nanotube density of 20%
resulted in a increase of conductivity by 15-fold
• Increasing the thickness of the P3HT layer aided
electron transfer
• Research should be done to improve the
transparency of the top film layer to be above 95%
Sources
Main Article:
1.
Nanotechnology for Next Generation Solar Cells. Prashant V. Kamat and George
C. Schatz. J. Phys. Chem. C, 2009.
http://pubs.acs.org/doi/full/10.1021/jp905378n?cookieSet=1#citing
Secondary Articles:
1.
Hiroshi Imahori and Tomokazu Umeyama. Donor−Acceptor Nanoarchitecture on
Semiconducting Electrodes for Solar Energy Conversion. J. Phys. Chem. C 2009.
http://pubs.acs.org/doi/abs/10.1021/jp9007448
2.
Wikipedia. Dye-sensitized solar cell. http://en.wikipedia.org/wiki/Dyesensitized_solar_cell
3.
Qifeng Zhang, Christopher S. Dandeneau, Xiaoyuan Zhou, Guozhong Cao. ZnO
Nanostructures for Dye-Sensitized Solar Cells. Advanced Materials. C 2009.
http://www3.interscience.wiley.com/cgi-bin/fulltext/122498586/PDFSTART
4.
Peter, L. M. Characterization and modeling of dye-sensitized solar cells. J. Phys.
Chem. C 2007. http://dx.doi.org/10.1021/jp069058b
5.
Prashant V. Kamat. Meeting the Clean Energy Demand: Nanostructure Architectures
for Solar Energy Conversion. J. Phys. Chem. C 2007.
http://pubs.acs.org/doi/full/10.1021/jp066952u
6.
Yasuhiro Tachibana, Kazuya Umekita, Yasuhide Otsuka, Susumu Kuwabata. Charge
Recombination Kinetics at an in Situ Chemical Bath-Deposited CdS/Nanocrystalline
TiO2 Interface. J. Phys. Chem. C, 2009, 113 (16), pp 6852–6858
http://pubs.acs.org/doi/full/10.1021/jp809042z
Group S1 Rebuttal
• Most of the comments were positive, which were
appreciated.
• Of the negative comments, while we agree with
most, the ones we don’t agree with was our
shortened introduction. We believe that our topic
was a continuation of the solar cell discussion Dr.
Seminario gave on the first day of class, and
therefore a long introduction was not needed.
Group S1
Group S2:
Review of Solar Technology
Chris Heflin
Rachael Houk
Michael Jones
Positives
• Group S1 was the first to present, and
therefore had a harder time knowing what to
expect with the presentation. However, they
presented a professional, well organized
presentation.
• Each presenter was knowledgeable on their
respective areas of the topic, spoke clearly
and fluently.
Negatives
• The group should make use of the
microphones and vocal projection in order to
be well heard. Everything was very quiet.
• Many of the slides contained only words and
no pictures, making the presentation less
interesting.
• Some of the material was a bit more technical
than most were prepared for. A bit more
introduction would be beneficial.
GROUP S3:
REVIEW OF SOLAR TECHNOLOGY
Bradford Lamb
Michael Koetting
James Kancewick
Week 1 Additional Slides
Seminar
Group S3
RECOMMENDATIONS
We felt S1 should have had more detailed
background slides towards solar technology.
 The information that they presented was
somewhat lost on the audience because it was
too detailed without having a solid background.
 Thus, we attached two additional slides that
improve background knowledge.

Group S3
GENERAL KNOWLEDGE
Solar powered electrical generation relies on
heat engines and photovoltaics
 limited only by human ingenuity
 most common way is to use solar panels
 Passive solar or active solar

Group S3
WATER TREATMENT
used to make saline or brackish water potable
 Solar energy may be used in a water
stabilization pond to treat waste water without
chemicals or electricity

Group S3
Group S4
Review of Solar Cell Technology
Joshua Moreno
Scott Marwil
Danielle Miller
Group S4
Things Done Well
• The group created a very nice power point
that was full of good visuals and rich
information
• The group spoke very clearly and made
minimal use of words like “um.”
• The group presented the material in a fun and
interesting way.
Group S4
Things That Need Improvement
• The group needs to try to not fit so much
information on every slide. The slides got a bit
wordy in some areas.
• The group needs to develop the introduction a
little bit more. We felt like it was too short
and did a poor job of leading into the
material.
Group S4
Group S5
Review of Solar Cell Technology
Group 5
Pradip Rijal
Jason Savatsky
Trevor Seidel
Laura Young
Group S5
Presentation Review
• The group overall did a very good job.
• They talked about the use of DSSC and
Quantum Dots being used in Solar Cells but
they did not tell us what they were.
• Organization was satisfactory.
• Could work on speaking louder.
Group S5
Critiqued by S6
Michael Trevathan
Daniel Arnold
Michael Tran
John Baumhardt
Group S6
Summary
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Discussed new solar cell efficiencies resulting
from nanotechnology
Needed to discuss the feasibility of this
technology becoming a substantial source of
energy
Needed more analysis on cost – at least some
estimated ranges based on the material
They all dressed nicely and spoke clearly
They were knowledgeable and directed their
attention toward the audience
Overall – great presentation!
Group S6