Improved Ga grading of sequentially produced Cu(In,Ga)Se₂ solar cells studied by high resolution X-ray fluorescence

There is particular interest to investigate compositional inhomogeneity of Cu(In,Ga)Se₂ solar cell absorbers. We introduce an approach in which focused ion beam prepared thin lamellas of complete solar cell devices are scanned with a highly focused synchrotron X-ray beam. Analyzing the resulting fluorescence radiation ensures high resolution compositional analysis combined with high spatial resolution. Thus, we are able to detect subtle variations of the Ga/(Ga + In) ratio down to 0.01 on a submicrometer scale. We observed that for sequentially processed solar cells a higher selenization temperature leads to absorbers with almost homogenous Ga/(Ga + In) ratio, which significantly improved the conversion efficiency.