Advanced large area characterization of thin-film solar modules by electroluminescence and thermography imaging techniques

This paper shows that the combination of both dark lock-in thermography (DLIT) and electroluminescence (EL) imaging techniques is especially suitable for in-depth shunt analysis of industrial Cu(In,Ga)Se2 (CIGS) thin-film modules and for the quantitative analysis of the local electrical cell properties, such as the internal junction voltage or the series resistances of the front and back contact. First results obtained for amorphous silicon (a-Si:H) based thin-film solar modules reveal that the quantitative EL analysis method is applicable to amorphous silicon technology as well. Using the consistent modeling of EL and DLIT images using a SPICE based model with input data generated from EL and DLIT measurements, we demonstrate that we can obtain properties of solar modules like the spatial voltage distribution, the resistances of the front and back contact, and the shunt resistance of local defects. We furthermore discuss two newly developed techniques, namely voltage-modulated lock-in thermography at the maximum power point (MPP-LIT) of an illuminated cell or module as well as differential EL analysis of illuminated cells and modules.