Nanoscale Surface Photovoltage Spectroscopy

Abstract

Understanding electron and ion dynamics is an important task for improving modern energy materials, such as photovoltaic perovskites. These materials usually have delicate nano- and microstructures that influence the device parameters. To resolve detailed structure–function relationships on the relevant micro- and nanometer length scales, the current macroscopic and microscopic measurement techniques are often not sufficient. Here, nanoscale surface photovoltage spectroscopy (nano-SPV) and nanoscale ideality factor mapping (nano-IFM) via time-resolved Kelvin probe force microscopy are introduced. These methods can map nanoscale variations in charge carrier recombination, ion migration, and defects. To show the potential of nano-SPV and nano-IFM, these methods are applied to perovskite samples with different morphologies. The results clearly show an improved uniformity of the SPV and SPV decay distribution within the perovskite films upon passivation and increasing the grain size. Nevertheless, nano-SPV and nano-IFM can still detect local variations in the defect density on these optimized samples, guiding the way for further optimization.