Bandgap Fluctuations Observed by EL in CIGS PV Modules
Matev˛ Bokalič1, Andreas Gerber2, Bart E. Pieters2, Uwe Rau2, Marko Topič1
1University of Ljubljana, Faculty of Electrical Engineering, Ljubljana, Slovenia
/2Forschungszentrum Jülich, IEK-5 Photovoltaik, Jülich, Germany

We applied a recently published electroluminescence method to image bandgap fluctuations on several CIGS modules. First we used a CIGS module with known apparent bandgap distribution to calibrate a two camera electroluminescence setup at University of Ljubljana for bandgap imaging. Imaging the module using the new calibration yields results similar to previously reported. Image analysis of additional five CIGS modules reveals spatial bandgap fluctuations across all modules. Average apparent bandgap value is within 1.11 eV to 1.13 eV range with average standard deviation of 0.02 eV. Observed fluctuation patterns often match between the modules with consecutive serial numbers, indicating that the fluctuations originate from systematic spatial variations in the production  process.

Area: Sub-Area 2.3: Cell and Module Characterization, Analysis, Theory, and Modeling