Numerical drift-diffusion modeling of organic solar cells in comparison with experimental data series

Abstract

Recently, much effort has been put in the simulation of charge transport in organic materials and more and more sophisticated models with an increasing number of parameters are developed. In this paper, we show which models are necessary and applicable for the drift-diffusion modeling of IV curves of multilayer solar cells. For comparison to experiment, a data series of small molecule organic solar cells comprising several materials, architectures, and thicknesses of layers is used. The model is chosen as simple as possible to reduce the number of parameters and to allow for the identification and accurate investigation of the key processes in detail. As exemplary result, the spatial exciton generation profile is examined within the active blend layer: It does not only influence the short circuit current, but also the fill factor and open circuit voltage at constant short circuit current, especially in the case of imbalanced mobilities. In another example where interfacial barriers are present, broadening of the energy levels due to disorder has to be taken into account to describe the IV curves showing S-Shape like behavior with realistic parameters. Transient measurements of extraction barrier devices show indeed an accumulation of charge carriers as predicted by simulation.