Identifying Local Variations in PV Material Properties via EBIC using In-Situ Light and Voltage Bias

Understanding the relationship between microstructure and excess charge carrier collection is key to the improvement of photovoltaic devices. Electron Beam Induced Current (EBIC) is a technique which creates a high-resolution spatial map of this excess charge carrier collection; however, it can be difficult to interpret due to the complex local variations in structure and chemistry characteristic of thin film devices. In this work we exploit the response of a CdTe device to applied light and voltage bias during the EBIC measurement in order to extract parameters related to the cause of collection variations in the EBIC map, namely local doping density and built-in potential of the p-n junction. Our results indicate that these parameters can vary from grain to grain within the polycrystalline film and can strongly impact grain boundary recombination behavior as well as overall collection profiles. In addition to a discussion of the physics associated with this measurement, we also use our results as input to a PV device model to estimate the impact of local variation on device performance.