Impact of a Doping-Induced Space-Charge Region on the Collection of Photogenerated Charge Carriers in Thin-Film Solar Cells Based on Low-Mobility Semiconductors

Abstract

Unintentional doping of the active layer is detrimental to an organic solar cell's performance, but is often overlooked. This work clarifies the impact of doping on charge-collection efficiency in low-mobility solar cells. By analytical derivation and numerical simulation, the authors find the collection efficiency of photogenerated charge carriers in a doped active layer to be independent of light intensity, but distinctly dependent on voltage, resulting in an electric field dependence of the photocurrent. The results will help to overcome the effect of unwanted doping, and to distinguish between different recombination loss mechanisms in these important photovoltaics.