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Ch.4: Polymer Solar Cells: Photoinduced Charge Transfer

C.B.  50fs. C 60 LUMO Level. ~ ms. C 60 HOMO Level. V.B. Conjugated Polymer. C 60. High Quantum Efficiency ~ 100%. Ch.4: Polymer Solar Cells: Photoinduced Charge Transfer. ▪ Photoinduced Electron Transfer between Conjugated Polymer and Fullerene.

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Ch.4: Polymer Solar Cells: Photoinduced Charge Transfer

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  1. C.B.  50fs C60 LUMO Level ~ ms C60 HOMO Level V.B. Conjugated Polymer C60 High Quantum Efficiency ~ 100% Ch.4: Polymer Solar Cells: Photoinduced Charge Transfer ▪ Photoinduced Electron Transfer between Conjugated Polymer and Fullerene N. S. Sariciftci & A. J. Heeger et al., Science 258 (1992) -Very efficient process faster than any other competing processes such as polaron, bipolaron, and exciton formation ( <50 fs ). -Back transfer is slowed down by forming polarons in C60. (>1 ms)

  2. ▪ Photoinduced Electron & Hole Transfer Photoinduced Charge Transfer Process (c.f. Photoinduced Energy Transfer) ▪ Experimental Evidence: LESR

  3. MEH-PPV:PCBM (95:5) • MEH-PPV:PCBM (90:10) • MEH-PPV:PCBM (80:20) • MEH-PPV:PCBM (50:50) Photoinduced Charge Transfer HOMO HOMO LUMO LUMO MEH-PPV PCBM ▪ Experimental Evidence: Luminescence Quenching

  4. ▪ Experimental Evidence: Photoconductivity Measurements Transient photoconductivity measurement C.H.Lee et al., Phys. Rev. B. 48, 15425 (1993). ▪ Experimental Evidence: Photoinduced Infrared Spectroscopy Infrared photoexcitation spectroscopy K.Lee, S. N. Saricifci, A. J. Heeger Phys. Rev. B. 49, 5781 (1994). C60- peak at 1.15 eV and 1.25 eV between t1u and t1g

  5. - + Al - e PEDOT:PSS + - ITO e- + Glass + Bicontinuous donor/acceptor bulk heterojunction Light + Light PCBM P3HT Interpenetrating Network in Polymer/C60 Composites G. Yu & A. J. Heeger et al., Science 270 (1995) - • Advantages • Bulk donor-acceptor • heterojunction • Achievement of large • interfacial area e • Requirements • Formation of percolation path • Morphology control Photovoltaic Cells using Polymer/C60 Composites

  6. HOMO HOMO Al ITO LUMO LUMO MEH-PPV PCBM Metal/Semiconductor/Metal structure Photovoltaic Effect in Polymer Solar Cells Typical PV effect in MEH-PPV/PCBM mixture

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