Cu2ZnSnS4 formation by co-evaporation and subsequent annealing in S-flux using molecular beam epitaxy system

Abstract

In this study, Cu2ZnSnS4(CZTS) formation by co-evaporation and subsequent annealing in S-flux was demonstrated using molecular beam epitaxy(MBE) system and the influence of the S-flux annealing temperature on the CZTS formation was investigated.At the films formed by co-evaporation of Cu, Zn, Sn and S at 320°C and subsequent annealing in S-flux at 320–450°C, CZTS and Cu2−xS phases were detected and those formations were found to have strong dependence on the S-flux annealing temperature. For annealing temperature, detected CZTS has maximum amount at the range of 380–420°C. On the other hand, detected Cu2−xS is minimum amount at that temperature range. Depth profile of those films showed that significant Cu segregation occurred to the film surface above 400°C of S-flux annealing temperature. These results suggest that the CZTS phase with less secondary phase of Cu2−xS, which has worse impact on the solar cell performance, is formed in the limited temperature range of 380–420°C of S-flux annealing performed after co-evaporation.2.25% power conversion efficiency was achieved at the solar cell with CZTS formed by the co-evaporation at 320°C and subsequent S-flux annealing at 400°C.