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How Molecular Structure Influences Device Performance in Organic Solar Cells

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

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How Molecular Structure Influences Device Performance in Organic Solar Cells

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  1. 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 Bad transfer Good transfer CF3-TNPS-Tet-Fu 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 = 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

  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

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