Effects of Masking on Open-Circuit Voltage and Fill Factor in Solar Cells

Guidelines for the correct measurement protocol of novel photovoltaic technologies are becoming more frequent in literature as it is not straightforward how to accurately measure the true efficiency parameters of laboratory solar cells. This is particularly the case for small-area research devices, which are prone to overestimate the short-circuit current density due to edge effects of various types. The common recommended practice is therefore to utilize masks with well-defined apertures. Herein we show both experimentally and theoretically that this common practice, however, leads to erroneous determination of both open-circuit voltage and fill factor, which are figures of merit of equal importance to the short-circuit current density. Although the errors induced in voltage and fill factor by using a mask are generally smaller than what the errors in current can amount to when not using a mask, they are, on the other hand, omnipresent and can be quite well described.