Optimization of Ga content and grading in the Solibro CIGS production line

In this paper we present results of the efficiency optimization study performed in our production line for CIGS solar modules. For three different Ga/(Ga+In) ratios two different grading settings were tested. Results indicate high impact of these parameters on efficiency, in the range of 0.5% (abs.). Increasing the Ga content in the film, results in an increase of module voltage. This is almost completely compensated by the decrease of Isc. The resulting change in efficiency is FF driven. The FF increases slightly with higher overall Ga content, but the grading plays a more important role. For the grading setting 1, which was steeper than the setting 2, the FF and consequently efficiency were significantly improved. Optimum Ga content and grading has been defined accordingly.