Carbon-Based Solar Cells
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Transcript of Carbon-Based Solar Cells
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Carbon-Based Solar Cells
Chabot College Guest Lecture
Michael VosgueritchianPhD Candidate
Prof. Zhenan Bao’s Group2-19-2013
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Research Overview Carbon and Organic Electronics
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Substrate
Sc-CNT
Anode
Cathode
IR light
ExcitonElectronhole
C60
• Silver or• PDMS / unsorted
CNT
CNT
P3DDT
• ITO / PEDOT or• Graphene
-3.8
-5.1
-4
-6.2
Sc-CNT C60
-4.7
e-
AgITO
-4.25-5
PEDOT
Active layerAnode Cathode
HOMO
LUMO
Graphene
-5.3
P3DDT
-3.5
-5.3
CNT
-4
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Current Energy World demand is 15 TW (15 trillion Watts)
Enough power for 15 billion 100W light bulbs US 26% (even though 5% of population)
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Source: cleantech.org
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Sustainable Energy
Wind Energy Solar Energy Ocean Energy Geothermal Energy Biofuel
In ~1 hr we get enough solar power to power the earth for a year!
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Source: Sandia National Lab
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Solar Radiation and Market Enough <1% of landmass enough to provide energy
demand
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Solar Cells Technologies
Crystalline Si – 27.6% Thin-Film
• CIGS – 20.4%• CdTE – 18.3%• α- Si - 13.4%
OPVs – 11.1% Nanotechnology
• Quantum Dots – 7.0% • Carbon based PVs (CPVs) – 1.2%* (~0.5%)
Other: GaAs, dye-sensitized, etc.
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NREL.com
GEKonerka
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Best Cell Efficiencies
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Solar Cell Uses and Considerations Applications
Industrial Commercial Home Portable
Considerations Cost/efficiency Materials Lifetime Niche applications
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NREL.com
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Portable Solar Cells
Uses Power portable
electronic devices Lighting Transportation
Lighting Africa Project Main failure due to
cracks in the solar cells
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Krebs et al. Energy Environ. Sci., 2010,3, 512-525
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Transparent Electrodes (TEs) Materials that offer high conductivity and
high transparency, usually in thin film form
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Displays
Sony.com
Solar Cells
• LEDs• Touch Screens• Energy Storage• Sensors• Transistors
Konarka.com
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Why do we Need New Alternative Electrodes? Replace ITO
Enable flexible (stretchable) organic electronics
Images from
Google 11
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Carbon PVs (CPVs) New class of solar cells
First demonstration of all-C solar Cell Stability
Chemical/Environmental: water/O2, heat, etc. Physical: strains, flexible/stretchable devices
Potential for cheap solar cells Solution processable Roll-to-roll fabrication Lightweight
Near-infrared absorption Tandem cells
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Carbon Nanomaterials
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Carbon Nanotubes (CNTs) – 1D• Discovered in 1991 • Single and multi-walled• Semiconducting or Metallic
Fullerenes – 0D• Discovered in 1985 (C60)• C60, C70, C84 • Films – n-type semiconducting
Graphene – 2D • Discovered in 2004• 2010 Nobel Prize• Metallic/transparent
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Solar Cell Operation
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Short Circuit Current (Jsc) High absorption Low recombination
Open circuit voltage (Voc) Optimum band gap
in
ocsc
PFFVJPCE
Fill factor (FF) Reduce parasitic
resistances
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CPV Structure Design of first demonstration of all-Carbon
solar cell Bilayer active layer: P3DDT sorted CNTs, C60 Electrodes
• Anode: ITO/PEDOT reduced graphene oxide (rGO)
• Cathode: Ag n-doped CNTs
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Substrate
Sc-CNT
Anode
Cathode
IR light
ExcitonElectronhole
C60
• Silver or• PDMS / unsorted
CNT
CNT
P3DDT
• ITO / PEDOT or• Graphene
-3.8
-5.1
-4
-6.2
Sc-CNT C60
-4.7
e-
AgITO
-4.25-5
PEDOT
Active layerAnode Cathode
HOMO
LUMO
Graphene
-5.3
P3DDT
-3.5
-5.3
CNT
-4
M. Vosgueritchian et al. ACS Nano, 2012, 6 (11), pp 10384–10395
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Film Fabrication
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Spray-CoatingSpin-Coating
Roll-to-roll Coater
Konerka.com
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Sorting of SC-SWNTs
Lee, H. W. et al. Nature Communication 2011, 2, 541 17
Solution based method to selective sort SWNTs Semiconducting
selectivity by P3DDT
Can be solution deposited: spin-coating, spray coating, etc.
Absorbs in the infrared (IR)
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Active Layer Bilayer of sorted SWNTs and C60
SWNT spin coated from solution C60 evaporated in vacuum
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1 2 3 4
50
100
150
200
250
300 Batch 1 Batch 2
Number of Layers
Shee
t Res
istan
ce
sq)
70
75
80
85
90
95
100
% Transm
ittance (at 550nm)
a) b)
Quartz Substrate
Sc-CNT
Reduced GO
n-doped SWNT
IR light
ExcitonElectronhole
C60
c)
400 600 800 1000 1200 1400 16000
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10
15
20
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40
Tran
smiss
ion (%
)
Wavelength (nm)
Drop casting, thin area Spin coating 5X Spin coating 3X Spin coating 1X
M. Vosgueritchian et al. ACS Nano, 2012, 6 (11), pp 10384–10395
Absorption Spectrum
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Anode – Graphene Can make large area electrodes
Smooth (2D) structure
Can be made highly conductive (30 ohms/sq at 90%)
Bae et al., Nature Nanotechnology 5, 574–578 (2010) 19
1 2 3 4
50
100
150
200
250
300 Batch 1 Batch 2
Number of Layers
Shee
t Res
istan
ce
sq)
70
75
80
85
90
95
100
% Transm
ittance (at 550nm)
a) b)
Quartz Substrate
Sc-CNT
Reduced GO
n-doped SWNT
IR light
ExcitonElectronhole
C60
c)
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Reduced Graphene Oxide
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1 2 3 4
50
100
150
200
250
300 Batch 1 Batch 2
Number of Layers
Shee
t Res
istan
ce
sq)
70
75
80
85
90
95
100
% Transm
ittance (at 550nm)
a) b)
Quartz Substrate
Sc-CNT
Reduced GO
n-doped SWNT
IR light
ExcitonElectronhole
C60
c)
Oxidation
Reduced Graphene Oxide (rGO)
thermal
reduction
Deposit on Surface by spin-coating
rGO– 2D• Solution Processable• 102-103 Ω/□ at ~80% T • Cheap H. Becerril et al. ACS Nano, 2008, 2 (3), pp 463–470
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Cathode – n-doped SWNT TE
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Use stretchable SWNT films on PDMS as the cathode for all-carbon solar cells instead of metal Need n-doping: DMBI organic dopant Previously used as electrodes in pressure an strain
sensors Spray-coated from solution
Biaxially stretched
As-deposited
1 μm1 μm
N
N
o-MeO-DMBI
OH
1 2 3 4
50
100
150
200
250
300 Batch 1 Batch 2
Number of Layers
Shee
t Res
istan
ce
sq)
70
75
80
85
90
95
100
% Transm
ittance (at 550nm)
a) b)
Quartz Substrate
Sc-CNT
Reduced GO
n-doped SWNT
IR light
ExcitonElectronhole
C60
c)
M. Vosgueritchian et al. Nature Nanotech, 2008, 2 , pp 788-792
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Device Performance
With traditional electrodes• ~0.5% Efficiency for full spectrum• ~0.2% Efficiency in the IR
With carbon electrodes• ~0.01% Efficiency full and IR
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Improving Performance Theoretical Efficiency of ~9-
10% Morphological Issues
Smoothen films: roughness/aggregates can cause leakage/shorting
Contact Issues Better contact between films:
better charge transport, decrease recombination
Active Layer Materials Use variety of SWNTs: increase
absorption Heterojunctions Thicker films
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Heterojunction
Electrodes Improve conductivity
Long Term Introduce flexibility Test stability All solution-processable
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SWNTs absorb mostly in the infrared Film thickness only about 5 nm Different deposition process
Absorption Issues
24800 1000 1200 1400 1600 1800
0.00
0.02
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0.12
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0.16
0.18
0.00
0.05
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0.20
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Abs
orba
nce
(a.u
.)
Opt
ical
pow
er in
tens
ity (m
W/c
m2 )
Wavelength (nm)
Light intensity with filter Absorbance semiconducting SWNT
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Summary First demonstration of all-carbon Solar Cell
Sorted-SWNTs used as light absorber C60 used to separate excitons Carbon electrodes replace traditional ITO/metal
electrodes Lots of work needs to be done! Acknowledgments
Prof. Zhenan Bao Dr. Marc Ramuz Dr. Ghada Koleilat Evan Wang Ben Naab
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QUESTIONS?
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