Mapping Voc in polycrystalline solar cells with nanoscale spatial resolution

The V_OC is a key parameter to determine the performance of a solar cell. In polycrystalline materials, it is imperative to find the origin of the modest V_OC that currently limits most PV technologies. For that, we implement a variant of Kelvin probe force microscopy to image and quantify local variations in the V_OC of a variety of thin film solar cells with spatial resolution <;100 nm, including CIGS and CdTe. We find that the V_OC varies locally by more than 200 mV, strongly indicating that spatial variation of non-radiative recombination greatly affects the overall device performance. Our functional imaging method paves the way for the rational design of polycrystalline solar cells with reduced centers for non-radiative recombination and improved performance.