CARBON NANOTUBE BASED ORGANIC SOLAR CELLS Arun Tej M. PhD Student EE Dept. and SCDT
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CARBON NANOTUBE BASED ORGANIC SOLAR CELLS
Arun Tej M.
PhD Student
EE Dept. and SCDT
• Carbon Nanotubes• Properties Useful for Solar Cells• Efficiency Limiting Factors• Nanotubes in Organic Solar Cells• Results and Future Challenges
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Outline
• S. Iijima - MWNT (1990), SWNT (1993)• Rolled graphene sheet with end caps• Large aspect ratios• Unique properties• Finds applications in
• Conductive plastics and adhesives• Energy storage• Efficient heat conduits• Structural composites• Biomedical devices
• Numerous electronic applications www.applied-nanotech.com
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Carbon Nanotubes
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Nanotube Field Emission Display
W.B. Choi, Samsung, APL, 1999
Thomas Rueckes, Nantero, 2000 5
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Nanotube Random Access Memory
Type of Memory
Most Important Feature
Applications
DRAM High Density Computer Operating Memory
SRAMFlash Memory
High SpeedNon-volatility
Cell Phones,Computer CachesPDAs, Cameras
MRAM High DensityHigh SpeedNon-volatility
All Uses
NRAM High DensityHigh SpeedNon-volatility
All Uses
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Nanotube Liquid Flow Sensor
A.K.Sood, IISc Bangalore, Science, 2003
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5 Stage Ring Oscillator on one SWNTZ.Chen, IBM, 2006
Nanotube Integrated Circuit
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Nanotube Based Inorganic Solar Cell
W.J.Ready, Georgia Tech, JOM, 2007
• High carrier mobilities (~1,20,000 cm2 V-1 s-1)
• Large surface areas (~1600 m2 g-1)
• Absorption in the IR range (Eg: 0.48 to 1.37 eV)
• Conductance - Independent of the channel length• Enormous current carrying capability – 109 A cm-2
• Semiconducting CNTs – Ideal solar cells• Mechanical strength & Chemical stability
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Nanotube Properties Useful for Solar Cells
Split-Gate device, Energy band diagram and I-V characteristics
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Combine the advantages of Organics and SWNTs 11
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Efficiency Improvement with SWNTs
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• Exciton dissociation sites• As electron acceptors in bulk heterojunction solar cells • Carrier transport• Thin transparent films of m-SWNTs as electrodes
Chhowalla et al, APL, 2005Wu et al, Science, 2004
Nanotubes in Organic Solar Cells
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Results (1)
Photoluminescence Quenching Higher Efficiency
Arun Tej M, S.S.K.Iyer, and B.Mazhari, IEEE INEC, 2008, Shanghai
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Results (2)
0 1 2 3 4 5 6 70
5
10
15
20
25
30
35
40
JP3HT
JSWNT (1wt%)
Cur
rent
Den
sity
(m
A/c
m2
)Forward Voltage
Negative resistanceregion showing tunneling behavior
Trap filling behaviour Tunneling behaviour
Arun Tej M, S.S.K.Iyer, and B.Mazhari, IEEE PVSC, 2008, San Diego
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0 20 40 60 80 1000.2
0.4
0.6
0.8
1.0
1.2
P3HT+SWNT (1wt%)
P3OT+SWNT (1wt%)
Op
en C
ircu
it V
olt
age
(v)
Light Intensity (mW cm-2)
High Voc of 1.15V at 1 Sun
High Open Circuit Voltages with Bulk Heterojunction Devices
Results (3)
Our WorkTo be published
• Synthesis of stable organic compounds• Separate semiconducting and metallic SWCNTs• Aligned CNTs inside the semiconducting polymers
give improved charge transport
e-
e-
e-
h+
h+
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h+
Future REACH (1)
• Add nanoparticles, quantum dots, fullerenes etc to the side walls of SWNTs
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e-
h+
h+
e-e-
h+
e-
h+
e-
Future REACH (2)
“A Solar Cell with Improved Light Absorption Capacity”
S. Sundar Kumar Iyer and Arun Tej M.Patent Appln. No. 933/DEL/2006
Dt: 31st March, 2006
New device structures
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Future REACH (3)
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Acknowledgements
• Faculty, Staff and Students, SCDT• Prof. Ashutosh Sharma, Chemical Engineering
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Schematic and energy diagram of a typical polymer solar cell and its operation
e-
h+
Anode Cathode Donor Acceptor
Exciton formation
Exciton diffusionExciton dissociationCarrier transport
Charge collection
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Organic Solar Cell
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Conjugated polymers Conduction due to
sp2– hybridised carbon atoms
and (pz-pz)bonds electrons are
delocalised in nature giving high electronic polarisability
High absorption in the UV-Visible range of the solar spectrum
H.Hoppe and N.S. Sariciftci, 2004
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METALLIC SWNTSMETALLIC SWNTS
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Conductance is independent of the channel length. 25
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Conductance through a barrier with transmission probability T.
Landauer Formula:
With N parallel 1D channels (subbands):
m-SWNTs: Only two subbands cross EF (N=2)
Source of R: Mismatch in the number of conduction channels in the SWNT and the macroscopic metal leads.
Th
eG
22
)(2
)(2
Fn
nF ETh
eEG
kR
Sh
e
h
eG
5.6~
1554
2*2 22
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