how molecular structure influences device performance in organic solar cells
DESCRIPTION
How Molecular Structure Influences Device Performance in Organic Solar Cells. Fullerene Derivatives Kirsten Parratt, Loo Lab, 11/9/2010. How it works. Photons absorbed by the organic compounds in the active layer create an exciton which diffuses randomly - PowerPoint PPT PresentationTRANSCRIPT
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How Molecular Structure Influences Device Performance in Organic Solar Cells
Fullerene Derivatives
Kirsten Parratt, Loo Lab, 11/9/2010
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How it works
• Photons absorbed by the organic compounds in the active layer create an exciton which diffuses randomly
• Upon reaching the acceptor and donor interface, the electron dissociates from the hole
• Both electron and hole are transported to their respective electrode
Al
ITO ITO ITO
AlAl
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Why Organic Solar Cells?
An alternative to silicon solar cells:• Easier manufacturing• Low temperature processing• Solution processing • Lower costs• Flexible substrates
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• P3HT/PCBM cells currently have one of the highest efficiencies (~5-6%)
• PCBM: [6,6]phenyl-C61-butyric acid methyl ester, acceptor small molecule
• P3HT: Poly(3-hexylthiophene), donor polymer
P3HT
PCBMITO
Al
3.7 eV
5.1 eV
PCBM
Electron Acceptor and Donor
Al
ITO
P3HT
LUMO
HOMO
Light
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• P3HT/PCBM cells currently have one of the highest efficiencies (~5-6%)
• PCBM: [6,6]phenyl-C61-butyric acid methyl ester, acceptor small molecule
• P3HT: Poly(3-hexylthiophene), donor polymer• Charge transport through pi orbitals
P3HT
PCBMITO
Al
3.7 eV
5.1 eV PCBM P3HT
Electron Acceptor and Donor
Light
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• P3HT/PCBM cells currently have one of the highest efficiencies (~5-6%)
• PCBM: [6,6]phenyl-C61-butyric acid methyl ester, acceptor small molecule
• P3HT: Poly(3-hexylthiophene), donor polymer
P3HT
PCBMITO
Al
3.7 eV
5.1 eV
Electron Acceptor and Donor
PCBM P3HT
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• P3HT/PCBM cells currently have one of the highest efficiencies (~5-6%)
• PCBM: [6,6]phenyl-C61-butyric acid methyl ester, acceptor small molecule
• P3HT: Poly(3-hexylthiophene), donor polymer
P3HT
PCBMITO Al
3.7 eV
5.1 eV
Electron Acceptor and Donor
PCBM P3HT
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Overview of Morphology-Length Scales
Molecular ordering
Crystal size
Phase separation
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• Systematically altered fullerene for better packing• How the molecules pack effects device
performance
CF3-TNPS-Tet-Fu TNPS-Tet-Fu TES-Tet-Fu
Structure/Function Relationship
J. Anthony
Large
Side group
Small
Side group
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Desired Stacking
• Contact between fullerenes should have better charge transfer
• Fullerene-acene contact will be worse• Best packing comes from the closest fullerenes
J. Anthony
Bad transfer
Good transfer
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Stacking
CF3-TNPS-Tet-Fu TNPS-Tet-Fu TES-Tet-Fu
J. Anthony
Good
Transport
Bad
Transport
Bad transfer
Good transfer
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Single Carrier Diodes
• Composed of only a fullerene
• No photocurrent generation• Measure the transport of
charge through the active layer
FullereneITO
PedotAl
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ue= (J0.5/V)2* L3*e0*er*8/9e0-permitivity of free space = 8.85418782 × 10-12 m-3 kg-1 s4 A2
er-dielectric constant = 3.9
- Measure of how fast charges can transport through the layer
Mobility
0 1 2 3 4
0.0
0.1
0.2
0.3
0.4
0.5
0.6[J
(m
A/c
m^
2)]
^0
.5
Voltage (V)
CF3-TNPS-Tet-Fu TNPS-Tet-Fu Tes-Tet-Fu
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Efficiency
-0.75 -0.50 -0.25 0.00 0.25-0.4
0.0
0.4
0.8
1.2
1.6
2.0
J (
mA
/cm
^2
)
Voltage (V)
Bilayer
Voc
Jsc
Maximum power
Efficiency = max power
100 mW/cm2
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Bilayer Comparison
• Jsc shows same trend as mobilities in SCD
• CF3-TNPS-Tet-Fu shows worst Jsc and device performance
-0.9 -0.6 -0.3 0.0 0.3
-0.06
0.00
0.06
0.12
0.18
0.24
J (
mA
/cm
^2
)
Voltage (V)
CF3-TNPS-Tet-Fu TNPS-Tet-Fu Tes-Tet-Fu
Efficiency (%)
3.3E-2
1.6E-3
4.77E-5
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Conclusion
• The observed mobilities and efficiencies show the same trends
• Most likely this trends correlates to the size of the side group
CF3-TNPS-Tet-Fu TNPS-Tet-Fu TES-Tet-Fu
Large Side group
Low efficiency
Small Side group
High efficiency
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Future Work
Crystallized derivatives would allow us to determine if the molecules are packing as planned– More through testing of solvent vapor and thermal
annealling– Thermal evaporation of the fullerene layer
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• Professor Loo • Stephanie Lee• Loo lab• PEI
Acknowledgements