Berlin 2005 – scientific programme

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SYOO: Organic Optoelectronics and Photonics

SYOO 5: Optoelectronic Devices

SYOO 5.3: Talk

Monday, March 7, 2005, 17:45–18:00, TU HE101

Influence of Morphology on the Photovoltaic Action of Polymer-Fullerene Composites — •Vladimir Dyakonov, Dana Chirvase, and Michael Pientka — Laboratory for Energy and Semiconductor Research, University of Oldenburg, Department of Physics, 26111 Oldenburg, Germany

Composites of polyhexylthiophen (P3HT) and methanofullerene (PCBM) are promising for polymer photovoltaics. External quantum efficiences above 70% and power conversion efficiencies above 3% were demonstrated recently. Decisive step to achieve such high values is a thermal annealing, strongly improving the electrical performance. The exact nature of this effect is still under discussion. We apply photoinduced absorption, light induced electron spin resonance and photoluminescence spectroscopy for the investigation of the photogenerated states and their transformation upon annealing. The heat treatment leads to a number of effects: increase of the photoluminescence previously suppressed, energy shift of polaronic absorption band together with a strong increase in the density of charge separated states. We have studied the performance of photovoltaic devices with a different weight ratio of P3HT:PCBM, namely, 1:3, 1:2, 1:1.5, 1:1, 1:0.9, 1:0.8, 1:0.7. The photocurrent and the power conversion efficiency showed a maximum between 1:1 and 1:0.9. We conclude the changes observed result from molecular diffusion of PCBM out of the polymer matrix upon annealing.