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HL: Fachverband Halbleiterphysik

HL 45: Organic photovoltaics and electronics

HL 45.2: Vortrag

Donnerstag, 15. März 2018, 15:15–15:30, EW 203

On the impact of capacity and transport on transient photovoltage measurements of organic solar cells — •Uli Würfel, Mathias List, and Moritz Unmüssig — Fraunhofer ISE, Heidenhofstr. 2, 79110 Freiburg, Germany

Transient photovoltage measurements (TPV) are applied to organic solar cells (OSC) to reveal recombination dynamics in these devices. From the recorded transients, charge carrier lifetimes are often derived by fitting an exponential function to the experimental data. In this contribution, numerical simulations of TPV experiments are presented which show that capacitive effects (due to very thin absorber layers) can have large impacts on the voltage transients which can lead - if not accounted for correctly - to questionable interpretations of TPV data. An analytical model describing generation, recombination and displacement current agrees very well with full numerical drift-diffusion simulations - but only for high charge carrier mobilities. In fact, the change in Voc can be dominated by the charge carrier mobilities, as the displacement current involves carrier transport in the absorber. Therefore we developed an expanded analytical model which takes explicitly into account the transport of charge carriers within the device. The results are in excellent agreement with full numerical drift-diffusion simulations for different absorber thicknesses and charge carrier mobilities and with experimental data. This shows that advancements in understanding recombination dynamics from photovoltage transients can only be achieved when properly considering carrier transport required for the displacement current.