A Simple Approach for Unraveling Optoelectronic Processes in Organic Solar Cells under Short-Circuit Conditions

The short-circuit current (J(sc)) of organic solar cells is defined by the interplay of exciton photogeneration in the active layer, geminate and non-geminate recombination losses and free charge carrier extraction. The method proposed in this work allows the quantification of geminate recombination and the determination of the mobility-lifetime product (mu tau) as a single integrated parameter for charge transport and non-geminate recombination. Furthermore, the extraction efficiency is quantified based on the obtained mu tau product. Only readily available experimental methods (current-voltage characteristics, external quantum efficiency measurements) are employed, which are coupled with an optical transfer matrix method simulation. The required optical properties of common organic photovoltaic (OPV) materials are provided in this work. The new approach is applied to three OPV systems in inverted or conventional device structures, and the results are juxtaposed against the mu tau values obtained by an independent method based on the voltage-capacitance spectroscopy technique. Furthermore, it is demonstrated that the new method can accurately predict the optimal active layer thickness.

Automated summary

The study introduces a new method to quantify exciton photogeneration, geminate and non-geminate recombination losses, and determine the mobility-lifetime product as an integrated parameter for charge transport and non-geminate recombination in organic solar cells. By utilizing common experimental methods and optical transfer matrix simulations, the new method accurately predicts the optimal active layer thickness.