the science behind dye-sensitized solar cells
DESCRIPTION
Brian Hardin of Stanford explains dye-sensitized solar cells.TRANSCRIPT
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The Dye Sensitized Solar CellBehind the Scenes of “Sunny Memories”
swissnex San Francisco 21 April 2010
Brian E. Hardin Stanford University
Filling in for:
Kevin Sivula Ecole Polytechnique Fédérale de Lausanne (EPFL)
Email: [email protected]
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Ecole Polytechnique Fédérale de Lausanne (EPFL)
• EPFL is one of the premier Science and Engineering Universities in Europe
• 6,000 Students • Over 100 Nationalities
with 50% of the teachers coming form outside of Switzerland.
• Michael Grätzel is the most highly cited solar scientist in the world. Grätzel lab is a five minute walk from Lac Léman
and beach volleyball courts.
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Dye-Sensitized Solar Cells are Photovoltaic Devices
mpmpPV VIP Power from Solar Cell:
On a sunny day, the power from the sun (Psun) is one kilowatt per meter
squared (1 kW/m2).
sun
PVPV P
PPower Conversion Efficiency:
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A new in paradigm in solar energy conversion
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Dye-Sensitized Solar Cell Components
Chemical Structure of N3 Dye
Sensitizing Dye Titania Nanoparticles
20 nm Titania nanoparticles
Electrolyte
Iodide/Tri-iodide Redox Couple
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Dye-Sensitized Solar Cell Schematic
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TiO2 Dye Electrolyte Cathode
Wide band-gap semiconductor
Current Generation in DSCs
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-0.5
0
0.5
TiO2
1.0
S*
S°/S+
Dye Electrolyte
OxRed
Cathode
Electron energy(eV vs. NHE)
-1.0
e-
Wide band-gap semiconductor
Current Generation in DSCs
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1. Light absorption -0.5
0
0.5
TiO2
1.0
S*
S°/S+
hν
Dye Electrolyte
OxRed
Cathode
1
Electron energy(eV vs. NHE)
-1.0
e-
Wide band-gap semiconductor
Current Generation in DSCs
h+
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1. Light absorption 2. Injection to
semiconductor3. Percolation
-0.5
0
0.5
TiO2
1.0
S*
S°/S+
hν
Dye Electrolyte
OxRed
Cathode
1
23
Electron energy(eV vs. NHE)
-1.0
e-
Wide band-gap semiconductor
Current Generation in DSCs
h+
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1. Light absorption 2. Injection to
semiconductor3. Percolation4. Regeneration of
oxidized dye
-0.5
0
0.5
TiO2
1.0
S*
S°/S+
hν
Dye Electrolyte
OxRed
Cathode
1
23
4
Electron energy(eV vs. NHE)
-1.0
Wide band-gap semiconductor
Current Generation in DSCs
e-
h+
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1. Light absorption 2. Injection to
semiconductor3. Percolation4. Regeneration of
oxidized dye5. Regeneration of
oxidized species
-0.5
0
0.5
TiO2
1.0
S*
S°/S+
hν
Dye Electrolyte
OxRed
Cathode
LOAD
e-
External circuit
1
23
4
Electron energy(eV vs. NHE)
-1.0
Wide band-gap semiconductor
Current Generation in DSCs
h+
5
h+
e-
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Maximum Voltage in DSCs
-0.5
0
0.5
TiO2
1.0
S*
S°/S+
Dye Electrolyte
OxRed
Maximum Voltage
Cathode
LOAD
e-
External circuit
Electron energy(eV vs. NHE)
-1.0
e-
Wide band-gap semiconductor
The voltage is determined mainly by the titania and redox couple in the electrolyte.
h+
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O’Regan and M. Gratzel, Nature 1991
Substrate
Dye monolayer
Dye Sensitized Mesoporous anatase TiO2
h+
Single crystal TiO2 ( <101> anatase)
Why Dye-Sensitized Solar Cells are nicknamed the “Grätzel Cell”
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Dye-Sensitized Solar Cells are 12% Efficient. What can we do to make
them better?
• Develop dyes to absorb more photons
• Create new electrolytes that provide higher voltages.
• Develop Dye-Sensitized Solar Cells that can last for 30 years
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Where do we need to absorb the light?
Solar Spectrum
400 600 800 1000 1200
0
1x1018
2x1018
3x1018
4x1018
5x1018
Ph
oto
ns/
(nm
m2
s)
Wavelength (nm)
AMA 1.5
Visible light Infrared Light
Dye-sensitized solar cells absorb >85% of visible light, but almost no light in the near-infrared.
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N
N
N
N
N
N
Ru
COOH
COOH
COOH
HOOC
HOOC
COOH
N
N
N
N
Ru
COOH
HOOC
HOOC
COOH
NC
S
NC
S
N
N
N
Ru
COOH
HOOC
HOOC N
C
S
NC
S
NC
S
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M.K. Nazeeruddin et al., J. Am. Chem.Soc. 123, 1613, (2001)
N749tri(cyanato)-2.22-terpyridyl-4,44-tricarboxylate)Ru(II)
N3cis-Ru(SCN)2L2
(L = 2,2-bipyridyl-4,4-dicarboxylate)
Design dyes that broadly absorb light
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Design Near-Infrared Absorbing Dyes
• Can increase power conversion efficiency from 12% to 14% by absorbing light out to 900 nm.
• Probably can’t make DSCs >14% using liquid electrolytes.
Stanford/EPFL collaboration through the Center for Advanced Molecular Photovoltaics (CAMP)
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Increase the maximum voltage using plastic hole conductors
-0.5
0
0.5
TiO2
1.0
S*
S°/S+
Dye Electrolyte
OxRed
Vliquid electrolyte
Cathode
LOAD
e-
External circuit
Electron energy(eV vs. NHE)
-1.0
e-
Wide band-gap semiconductor
Bach & Grätzel, Nature 1999
New Hole Conductors
Potential to make >20% efficient devices by replacing liquid electrolyte with plastic “solid-state” hole conductors.
Current “solid-state” DSCs are only 6.5% efficient.
Very promising research area.
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Aesthetic Advantages of Grätzel Cells versus conventional Solar Devices
• Dyes determine the color of the device.
• Can be transparent
• Can be flexible
• Easy to make
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Solar Powered Solar Panel Sun GlassesThe SIG, or “Self-Energy Converting Sunglasses” are quite simple. The lenses of the glasses have dye solar cells, collecting energy and making it able to power your small devices through the power jack at the back of the frame. “Infinite Energy: SIG”
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Module UnitModule Unit Outdoor TestOutdoor Test
Real Outdoor Test of DSC Modules Real Outdoor Test of DSC Modules
Series connected 64 DSC cells
Kariya City at lat. 35°10’N, Asimuthal angle: 0°Facing due south, Tilted at 30°
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High School Students make their own solar cellHigh School Students make their own solar cell
anthocyanine dye from blackberries
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Stanford University, KAUST Center for Advanced Molecular Photovoltaics (CAMP),
Swiss CTI , CCEM-CHSwiss National Science Foundation, Swiss Energy OfficeUS Air Force (European Office of Aerospace
Research and Development)FP7 European Joule Projects: DSC-ROBUST *,
NANOPEC, INNOVASOLEuropean Research Council, Adv. Res. Grant.GRL Korea (with KRICT)Industrial Partners,
We are grateful for funding from:
* DSC-Robust project coordinated by ECN Patten , This proposal received highest rating (15/15) of all proposals in energy field during first EU-FP7 call.
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The DSC vs. Conventional Silicon PV
TiO2
Dye
Electrolyte
Cathode
Light
+
R n-typeSilicon
p-typeSilicon
+ R
+ R
+ R+ R
•Charge carriers (excited electrons) are produced throughout the semiconductor•Semiconductor considerations:
• Precise doping• high purity• high crystalinity
•Light absorption and charge transport are decoupled •Relaxed constraints on individual components (each can be separately tuned)•Only monolayer of dye on TiO2
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Solar Cell Efficiencies
Silicon Solar Cell Efficiencies:
Theoretical Maximum: 26%
Best in Lab: 25% (Green, UNSW)
Modules: 15-22%
Thin Film Solar Cell Efficiencies:
Theoretical Maximum: >22%
Best in Lab: 20% (Noufi, NREL)
Modules: 9-12%
Dye-Sensitized Solar Cell Efficiencies:
Theoretical Maximum: 14-20%
Best in Lab: 12% (Grätzel, EPFL)
Modules: 6-9%