Quantitative evaluation method for electroluminescence images of a-Si:H thin-film solar modules

This work presents a method for extracting the absolute local junction voltage of a‐Si:H thin‐film solar cells and modules from electroluminescence (EL) images. It is shown that the electroluminescent emission of a‐Si:H devices follows a diode law with a radiative ideality factor nr larger than one. We introduce an evaluation method that allows us to determine the absolute local junction voltage in cases of nr > 1, while existing approaches rely on the assumption of nr = 1. Furthermore, we find that the experimentally determined values of nr vary from sample to sample. It is also explained why the derived radiative ideality factor is influenced by the spectral sensitivity of the camera system used in the experiment. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) In this Letter, the authors demonstrate a method to extract the absolute local junction voltage of hydrogenated amorphous silicon thin‐film solar cells and modules from electroluminescence images. Thereby, an ideality factor nr larger than one is derived which depends on the device and the spectral sensitivity of the camera system used in the experiment.