Understanding the Light-Intensity Dependence of the Short-Circuit Current of Organic Solar Cells

In organic solar cells, bimolecular recombination is a key factor limiting the device performance and creating the need for characterization. Light-intensity-dependent short-circuit current density measurements are a frequently used tool to qualitatively analyze bimolecular recombination in a device. When applying a 0D model, bimolecular recombination is expected to reduce the otherwise linear correlation of the short-circuit current densityJ(sc)and the light intensity phi to a sublinear trend. It is shown by numerical simulations that the slope of the J(sc)-phi curve is affected by the recombination mechanism (direct or via traps), the spatial distribution of charge carriers and-in thick solar cells-by space charge effects. Only the combination of these effects allows proper explanation of the different cases, some of which cannot be explained in a simple 0D device model.