Quantitative electroluminescence analysis of resistive losses in Cu(In, Ga)Se2 thin-film modules

Cu(In,Ga)Se2 mini-modules are investigated by electroluminescence imaging under different bias voltage conditions. The images typically show 10–20 localized shunts on the investigated test modules of an area of 20×17 cm2 with 42 cells. The consequences of these shunts on the performance of the individual cells and of the entire module are quantitatively analyzed by evaluating the electroluminescence images. Our analysis considers the electroluminescence intensity at each surface position of the module to depend on the actual voltage drop across the junction at this specific location. Hence, the analysis of the electroluminescence intensity permits the reconstruction of the current/voltage characteristics of all individual cells of the module. Additionally, we determine the sheet resistance of the ZnO window layer and the Mo back contact from the spatial dependence of the electroluminescence intensity across one solar cell in the module.