Berlin 2015 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 30: P2: Organic Electronics and Photovoltaics

CPP 30.6: Poster

Tuesday, March 17, 2015, 14:00–16:00, Poster B

Hot charges speed up non geminate recombination but have no effect on device performance — •Jona Kurpiers, Steve Albrecht, and Dieter Neher — Institute of Physics and Astronomy, Soft Matter Physics, University of Potsdam, D-14476 Potsdam

In this work, we use time delayed collection field (TDCF) experiments with exceptionally high time resolution to investigate the charge carrier dynamics in the PCDTBT:PC70BM system. Although this system has a high fill factor of around 70% and an internal quantum efficiency approaching unity under steady state illumination conditions, TDCF experiments reveals non-geminate recombination on the 10 ns time-scale, even for charge carrier densities comparable to one sun illumination. This loss becomes significantly accelerated at higher pulse fluence. To identify the reason for this rapid loss, the recombination dynamics was further investigated with constant white light background illumination, which introduces a tunable steady state carrier density, and on thicker devices. We observe that the short term decay dynamics is not affected by the background carrier density. It is concluded that the main reason for the nongeminate loss observed at the 10 ns time scale is recombination of hot charges close to the contacts. As recombination occurs mainly between hot electrons and holes, this loss channel seems to be insignificant under steady state illumination. Our result imply that transient experiments, considering the dynamics of *freshly-generated* charges should be considered with great care when aiming at the understanding of device function under steady-state illumination conditions.