The role of buffer/kesterite interface recombination and minority carrier lifetime on kesterite thin film solar cells

Abstract

This paper presents for the first time a theoretical study of the impact of kesterite/buffer interface recombination and kesterite minority carrier lifetime on both CZTS and CZTSe solar cells. It demonstrates that only an 11% efficiency can be reached in CZTS solar cells by improving absorber crystalline quality, pointing out the need for an improved CdS/CZTS interface. It further demonstrates that a CZTS solar cell efficiency enhancement of up to 18%, with an open-circuit voltage value of up to 918 mV, can be achieved depending on CZTS minority carrier lifetime and CdS/CZTS interface recombination speed values. Moreover, this paper shows that by improving CZTSe crystalline quality, a record efficiency value of 17% could be achieved without focusing on improving CdS/CZTSe interface quality. Consequently, CZTSe is presented as a better candidate for solar cell applications. Conditions under which CdS/kesterite interface recombination and trap-assisted tunneling recombination become dominant are provided. In particular, we find that CdS/CZTS interface recombination is the dominant transport mechanism for CZTS minority carrier lifetime values higher than 5 ns, while for CZTSe minority carrier lifetime values lower than 0.1 μs, CdS/CZTSe interface losses are negligible.