Berlin 2015 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 19: Organic photovoltaics and electronics - mostly properties of the absorber (with DS)

HL 19.7: Talk

Monday, March 16, 2015, 18:30–18:45, EW 202

Mobility Relaxation in PTB7:PC₇₀BM on nanosecond timescale — •Andreas Fritze¹, Andreas Sperlich¹, Carsten Deibel², and Vladimir Dyakonov^1,3 — ¹Experimental Physics VI, Julius Maximilian University of Würzburg, 97074 Würzburg — ²Institute of Physics, Chemnitz University of Technology, 09107 Chemnitz — ³ZAE Bayern, 97074 Würzburg

For photovoltaics, charge carrier lifetime is an essential parameter due to its influence on short circuit current, and thus on power conversion efficiency. In organic photovoltaics, for several material systems, charge carrier lifetime exceeds predictions from recombination models by orders of magnitude. In literature, this phenomenon is discussed in the context of reduced langevin recombination, for instance the high-efficiency bulk heterojunction polymer fullerene solar cell PTB7:PC₇₀BM, it is shown that recombination is also reduced. However, the physical processes responsible for these low recombination rates, such as mobility relaxation, energetic traps, and morphological traps, are hard to observe separately. Here, we present simultaneous transient absorption (TA) and transient microwave conductivity (TRMC) measurements on PTB7:PC₇₀BM films. From the experimental data we calculate time dependent mobility, since TA is sensitive to charge carrier density and TRMC is sensitive to conductivity. A relaxation of mobility on these time scales is measured the first time separately. Thus, we can distinguish mobility relaxation from other recombination influencing processes in PTB7:PC₇₀BM.