Carbon-Based Solar Cells Chabot College Guest Lecture Michael Vosgueritchian PhD Candidate

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Carbon-Based Solar Cells
Chabot College Guest Lecture
Michael Vosgueritchian
PhD Candidate
Prof. Zhenan Bao’s Group
2-19-2013
1
Research Overview

Carbon and Organic Electronics
• Silver or
• PDMS / unsorted
CNT
IT
IR light
Cathode
C60
Exciton
Electron Sc-CNT
hole
Anode
Substrate
CNT
P3DDT
• ITO / PEDOT or
• Graphene
2
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)
Source: cleantech.org
3
Sustainable Energy





Wind Energy
Solar Energy
Ocean Energy
Geothermal Energy
Biofuel
Source: Sandia National Lab

In ~1 hr we get enough solar power to power the earth
for a year!
4
Solar Radiation and Market


Enough
<1% of landmass enough to provide energy demand
5
Solar Cells

Technologies





NREL.com
Crystalline Si – 27.6%
Thin-Film
• CIGS – 20.4%
• CdTE – 18.3%
Konerka
• 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.
GE
6
Best Cell Efficiencies
7
Solar Cell Uses and Considerations

Applications





Industrial
Commercial
Home
Portable
Considerations




Cost/efficiency
Materials
Lifetime
Niche applications
NREL.com
8
Portable Solar Cells

Uses




Power portable electronic
devices
Lighting
Transportation
Lighting Africa Project

Main failure due to cracks
in the solar cells
Krebs et al. Energy Environ. Sci., 2010,3, 512-525
9
Transparent Electrodes (TEs)

Materials that offer high conductivity and high
transparency, usually in thin film form
Displays
Solar Cells
• LEDs
• Touch Screens
• Energy Storage
• Sensors
• Transistors
Sony.com
Konarka.com
10
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


Stability



Chemical/Environmental: water/O2, heat, etc.
Physical: strains, flexible/stretchable devices
Potential for cheap solar cells




First demonstration of all-C solar Cell
Solution processable
Roll-to-roll fabrication
Lightweight
Near-infrared absorption

Tandem cells
12
Carbon Nanomaterials
Fullerenes – 0D
• Discovered in 1985 (C60)
• C60, C70, C84
• Films – n-type semiconducting
Carbon Nanotubes (CNTs) – 1D
• Discovered in 1991
• Single and multi-walled
• Semiconducting or Metallic
Graphene – 2D
• Discovered in 2004
• 2010 Nobel Prize
• Metallic/transparent
13
Solar Cell Operation
PCE 

Short Circuit Current (Jsc)



J sc Voc  FF
Pin
High absorption
Low recombination

Fill factor (FF)

Reduce parasitic resistances
Open circuit voltage (Voc)

Optimum band gap
14
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


• Silver or
• PDMS / unsorted
CNT
IR light
Graphene
Exciton
Electron Sc-CNT
hole
Anode
Substrate
-3.5
-3.8 e
CNT
-4.7
P3DDT
• ITO / PEDOT or
• Graphene
CNT
PEDOT Sc-CNT C60
ITO
Cathode
C60
P3DDT
-5.3
-5
-5.1
-5.3
Anode
M. Vosgueritchian et al. ACS Nano, 2012, 6 (11), pp 10384–10395
-4
Ag
-4
-4.25
-6.2
LUMO
HOMO
Active layer Cathode
15
Film Fabrication
Spin-Coating
Spray-Coating
Roll-to-roll Coater
Konerka.com
16
Sorting of SC-SWNTs

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)
Lee, H. W. et al. Nature Communication 2011, 2, 541
17
a)
300


Sheet Resistance sq)
85
150
80
100
75
50
70
1
2
3
IR light
n-doped SWNT
C60
Exciton
Electron
hole
Sc-CNT
Reduced GO
4
Number of Layers
Quartz Substrate
SWNT spin coated from solution
C60 evaporated in vacuum
Absorption Spectrum
35
30
Transmission (%)
90
200
c)
Bilayer of sorted SWNTs and C60

40
95
% Transmittance (at 550nm)
Active Layer
b)
100
Batch 1
Batch 2
250
Drop casting, thin area
Spin coating 5X
Spin coating 3X
Spin coating 1X
25
20
15
10
5
0
400
600
800
1000
1200
1400
1600
Wavelength (nm)
M. Vosgueritchian et al. ACS Nano, 2012, 6 (11), pp 10384–10395
18
a)
300
95
90
200
85
150
Anode – Graphene
80
100
75
50
1
% Transmittance (at 550nm)
Sheet Resistance sq)
b)
100
Batch 1
Batch 2
250
c)
IR light
n-doped SWNT
C60
Exciton
Electron
hole
70
2
3
Sc-CNT
Reduced GO
4
Number of Layers
Quartz Substrate

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
a)
300
Sheet Resistance sq)
90
200
85
150
% Transmittance (at 550nm)
95
c)
b)
100
Batch 1
Batch 2
250
n-doped SWNT
Reduced Graphene Oxide
80
100
75
50
70
1
2
3
Number of Layers
IR light
C60
Exciton
Electron
hole
Sc-CNT
Reduced GO
4
Quartz Substrate
Oxidation
thermal
reduction
Reduced Graphene Oxide (rGO)
rGO– 2D
• Solution Processable
• 102-103 Ω/□ at ~80% T
• Cheap
Deposit on Surface by spin-coating
H. Becerril et al. ACS Nano, 2008, 2 (3), pp 463–470
20
a)
300
Sheet Resistance sq)
90
200
85
150
% Transmittance (at 550nm)
95
c)
b)
100
Batch 1
Batch 2
250
n-doped SWNT
Cathode – n-doped SWNT TE
80
100
75
50
IR light
C60
Exciton
Electron
hole
70
1
2
3
Reduced GO
4
Number of Layers

Sc-CNT
Quartz Substrate
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
As-deposited
Biaxially
stretched
1 μm
M. Vosgueritchian et al. Nature Nanotech, 2008, 2 , pp 788-792
1 μm
21
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


Contact Issues


Smoothen films:
roughness/aggregates can cause
leakage/shorting
Better contact between films: better
charge transport, decrease
recombination

Electrodes


Improve conductivity
Long Term



Introduce flexibility
Test stability
All solution-processable
Heterojunction
Active Layer Materials



Use variety of SWNTs: increase
absorption
Heterojunctions
Thicker films
23
Absorption Issues
0.18
0.16
0.25
Light intensity with filter
Absorbance semiconducting SWNT
0.20
0.14
0.12
0.15
0.10
0.08
0.10
0.06
0.04
Absorbance (a.u.)

2

SWNTs absorb mostly in the infrared
Film thickness only about 5 nm
Different deposition process
Optical power intensity (mW/cm )

0.05
0.02
0.00
800
1000
1200
1400
Wavelength (nm)
1600
0.00
1800
24
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
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