Selenium and arsenic interactions in CdSeTe/CdTe solar cells using STEM-EDX, NanoSIMS and cathodoluminescence

Thin film CdSeTe/CdTe solar cells were fabricated using an unusually high concentration of arsenic dopants. The devices were processed in the usual way including a cadmium chloride activation annealing process. Device cross-sections were then prepared using focused ion beam milling and characterized using STEM, EDX, NanoSIMS and Cathodoluminescence. The device was also cleaved at the junction using liquid nitrogen. The STEM/EDX cross-sections reveal a distorted Se distribution across the device. Selenium and Arsenic show preferential migration in grain boundaries. Unusually, the analysis revealed a strong interaction occurs between Selenium and Arsenic. The analysis shows that the presence of Arsenic may form a barrier to the movement of Selenium during the recrystallisation that occurs during the cadmium chloride recrystallisation. This device was specially prepared to investigate the effect of untypical arsenic dopant levels. Such unusual selenium profiles are not typically observed but the experiment does reveal an interesting interaction between selenium and arsenic.