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TT: Fachverband Tiefe Temperaturen

TT 47: Organic Electronics and Photovoltaics: OPV I (jointly with CPP, HL, O)

TT 47.5: Vortrag

Dienstag, 17. März 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 Dyakonov^1,3 — 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.