Berlin 2015 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 36: Organic electronics and photovoltaics: OPV I (CPP with HL/TT)
HL 36.5: Talk
Tuesday, March 17, 2015, 15:15–15:30, C 130
Photoinduced Dynamics of Charge Separation: from Photosynthesis to Polymer-Fullerene Bulk-Heterojunctions — •Andreas Sperlich1, Oleg G. Poluektov2, Jens Niklas2, and Vladimir Dyakonov1,3 — 1Experimental Physics VI, Julius Maximilian University of Würzburg, 97074 Würzburg — 2Chemical Sciences and Engineering Division, ANL, Argonne, Illinois 60439, USA — 3ZAE Bayern, 97074 Würzburg
Understanding charge separation and charge transport is crucial for improving the efficiency of organic solar cells. This is due to the excitonic nature of their active media, based on organic molecules, serving as both a light absorbing and transport layer. Charge transfer (CT) states play an important role, being intermediate for free carrier generation and charge recombination. Here, we use light-induced electron paramagnetic resonance (EPR) spectroscopy to study the charge transfer dynamics in composites of the polymers P3HT, PCDTBT, and PTB7 with the fullerene derivative PC60BM. Transient EPR measurements show strong spin-polarization patterns for all polymer-fullerene blends, confirming predominant generation of singlet CT states. These observations allow a comparison with charge separation processes in molecular donor-acceptor systems, as found in natural and artificial molecular photosynthetic systems and clarification of the initial steps of sequential charge transfer in organic photovoltaic (OPV) materials. The detection of strong electron spin-polarization in OPV materials points out to the significance of spin dynamics for the efficient functioning of solar cell devices.