1. Fullerene Derivatives Kirsten Parratt, Loo Lab, 11/9/2010
How Molecular Structure Influences Device Performance in Organic Solar Cells
Fullerene Derivatives
Kirsten Parratt, Loo Lab, 11/9/2010

2. 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 Al Al
ITO
ITO
ITO

3. Why Organic Solar Cells?
An alternative to silicon solar cells:
Easier manufacturing
Low temperature processing
Solution processing
Lower costs
Flexible substrates

4. Electron Acceptor and Donor
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
LUMO
3.7 eV
5.1 eV Al
P3HT
P3HT
ITO
PCBM
PCBM Al
HOMO
ITO
Light

5. Electron Acceptor and Donor
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
Light
3.7 eV
5.1 eV Al
P3HT
ITO
PCBM
PCBM P3HT

6. Electron Acceptor and Donor
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
3.7 eV
5.1 eV Al
P3HT
ITO
PCBM
PCBM P3HT

7. Electron Acceptor and Donor
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
3.7 eV
5.1 eV
P3HT Al
ITO
PCBM
PCBM P3HT

8. Overview of Morphology-Length Scales
Molecular ordering
Crystal size
Phase separation

9. Structure/Function Relationship
Systematically altered fullerene for better packing
How the molecules pack effects device performance
CF3-TNPS-Tet-Fu TNPS-Tet-Fu TES-Tet-Fu
Large
Side group
Small
Side group
J. Anthony

10. Desired Stacking
Bad transfer
Good transfer
Contact between fullerenes should have better charge transfer
Fullerene-acene contact will be worse
Best packing comes from the closest fullerenes
J. Anthony

11. Stacking J. Anthony Bad transfer Good transfer CF3-TNPS-Tet-Fu
TES-Tet-Fu
Good
Transport
Bad
Transport
J. Anthony

12. Single Carrier Diodes Composed of only a fullerene
No photocurrent generation
Measure the transport of charge through the active layer
ITO
Fullerene
Pedot Al

13. Mobility ue= (J0.5/V)2* L3*e0*er*8/9
e0-permitivity of free space = × m-3 kg-1 s4 A2
er-dielectric constant = 3.9
- Measure of how fast charges can transport through the layer

14. Efficiency
Jsc
Efficiency = max power
100 mW/cm2
Maximum power
Voc

15. Bilayer Comparison Jsc shows same trend as mobilities in SCD
CF3-TNPS-Tet-Fu shows worst Jsc and device performance
Efficiency (%)
3.3E-2
1.6E-3
4.77E-5

16. 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

17. 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

18. Acknowledgements
Professor Loo
Stephanie Lee
Loo lab
PEI