Dresden 2011 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 8: Poster: Organic Semiconductors

CPP 8.7: Poster

Monday, March 14, 2011, 17:30–19:30, P2

Charge Generation and Recombination in PCDTBT:PCBM Photovoltaic Blends — •Fabian Etzold, Ian Howard, Ralf Mauer, Michael Meister, and Frédéric Laquai — Max Planck Institute for Polymer Research, Mainz, Germany

Low-bandgap donor-acceptor copolymers have recently demonstrated their potential in bulk heterojunction organic solar cells. Among them, poly[N-9’-heptadecanyl-2,7-carbazole-alt-5,5-(4’,7’-di-2-thienyl-2’,1’,3’-benzothiadiazole)] (PCDTBT) blended with fullerene derivatives proved to be very efficient, yielding power conversion efficiencies in excess of  3 % even without postproduction annealing, which is typically applied to polythiophene:fullerene blends. We investigate exciton dynamics in pristine PCDTBT and charge carrier dynamics in as-cast and annealed blends with [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) by transient absorption and time-resolved photoluminescence spectroscopy. We find that in PCDTBT:PCBM blends a large fraction of excitons undergoes ultrafast generation of free charge carriers as previously observed for other material systems including P3HT:PCBM. However, a fraction of interfacial charge transfer states is also created, which recombine geminately with a lifetime of  2.5 ns. By monitoring the recombination dynamics over the previously unobserved time range from 1 ns to 1 ms, we conclude that the device efficiency must be limited by geminate recombination and charge extraction.