Regensburg 2013 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 77: Organic electronics and photovoltaics IV (CPP, jointly with DS, HL, O)

HL 77.6: Talk

Thursday, March 14, 2013, 11:00–11:15, H34

Charge generation and recombination in PCPDTBT:PCBM and PSBTBT:PCBM bulk heterojunction photovoltaic blends — •Fabian Etzold, Ian Howard, Michael Meister, and Frédéric Laquai — Max Planck Research Group for Organic Optoelectronics, Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany

We present a comparative study of the photophysical processes leading to photocurrent generation and photocurrent loss in photovoltaic blends of the low-bandgap polymer PCPDTBT with PCBM and its silicon-substituted analogue PSBTBT with PCBM studied by Vis-NIR transient absorption pump-probe spectroscopy and variable time-delay double-pump photocurrent extraction experiments. Our experiments demonstrate that the power conversion efficiency of PCPDTBT:PCBM blends is largely limited by sub-nanosecond geminate recombination of interfacial charge-transfer states plus fast non-geminate recombination of free charges competing efficiently with charge extraction. In comparison photovoltaic blends of the silicon-substituted polymer PSBTBT with PCBM exhibit significantly less geminate recombination in conjunction with much slower non-geminate recombination of free charges leading in turn to substantially higher photocurrents and fill factors and thus overall increased photovoltaic performance. We also observed a pronounced excitation wavelength dependence of the photophysical processes occurring after excitation of either the polymer or the fullerene component of the blend at different photon energies. [1] F. Etzold et al., J. Am. Chem. Soc. 2012, 134 (25), 10569-10583.