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Chabot College Guest Lecture Michael Vosgueritchian PhD Candidate Prof. Zhenan Bao’s Group 2-19-2013. Carbon-Based Solar Cells. Research Overview. Carbon and Organic Electronics. Current Energy. World demand is 15 TW (15 trillion Watts) Enough power for 15 billion 100W light bulbs - PowerPoint PPT Presentation
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Carbon-Based Solar Cells
Chabot College Guest Lecture
Michael VosgueritchianPhD Candidate
Prof. Zhenan Bao’s Group2-19-2013
1
Research Overview Carbon and Organic Electronics
2
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
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)
3
Source: cleantech.org
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!
4
Source: Sandia National Lab
Solar Radiation and Market Enough <1% of landmass enough to provide energy
demand
5
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.
6
NREL.com
GEKonerka
Best Cell Efficiencies
7
Solar Cell Uses and Considerations Applications
Industrial Commercial Home Portable
Considerations Cost/efficiency Materials Lifetime Niche applications
8
NREL.com
Portable Solar Cells
Uses Power portable
electronic devices Lighting Transportation
Lighting Africa Project Main failure due to
cracks in the solar cells
9
Krebs et al. Energy Environ. Sci., 2010,3, 512-525
Transparent Electrodes (TEs) Materials that offer high conductivity and
high transparency, usually in thin film form
10
Displays
Sony.com
Solar Cells
• LEDs• Touch Screens• Energy Storage• Sensors• Transistors
Konarka.com
Why do we Need New Alternative Electrodes? Replace ITO
Enable flexible (stretchable) organic electronics
Images from
Google 11
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
12
Carbon Nanomaterials
13
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
Solar Cell Operation
14
Short Circuit Current (Jsc) High absorption Low recombination
Open circuit voltage (Voc) Optimum band gap
in
ocsc
PFFVJPCE
Fill factor (FF) Reduce parasitic
resistances
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
15
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
Film Fabrication
16
Spray-CoatingSpin-Coating
Roll-to-roll Coater
Konerka.com
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)
Active Layer Bilayer of sorted SWNTs and C60
SWNT spin coated from solution C60 evaporated in vacuum
18
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
5
10
15
20
25
30
35
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
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)
Reduced Graphene Oxide
20
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
Cathode – n-doped SWNT TE
21
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
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
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
23
Heterojunction
Electrodes Improve conductivity
Long Term Introduce flexibility Test stability All solution-processable
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
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.00
0.05
0.10
0.15
0.20
0.25
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
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
25
QUESTIONS?
26