Characterization of Cu2ZnSnSe4 Thin Films Selenized with Cu2-xSe/SnSe2/ZnSe and Cu/SnSe2/ZnSe Stacks

Abstract

Cu2ZnSn(S,Se)4 material is receiving an increased amount of attention for solar cell applications as an absorber layer because it consists of inexpensive and abundant materials (Zn and Sn) instead of the expensive and rare materials (In and Ga)in Cu(In,Ga)Se2 solar cells. We were able to achieve a cell conversion efficiency to 4.7% by the selenization of a stacked metal precursor with the Cu/(Zn + Sn)/ Mo/glass structure. However, the selenization of the metal precursor results in large voids at the absorber/Mo interface because metals diffuse out through the top CZTSe layer. To avoid the voids at the absorber/Mo interface, binary selenide compounds of ZnSe and SnSe2 were employed as a precursor instead of Zn and Sn metals. It was found that the precursor with Cu/SnSe2/ZnSe stack provided a uniform film with larger grains compared to that with Cu2Se/SnSe2/ZnSe stack. Also, voids were not observed at the Cu2ZnSnSe4/Mo interface. A severe loss of Sn was observed after a high-temperature annealing process, suggesting that selenization in this case should be performed in a closed system with a uniform temperature in a SnSe2 environment. However, in the experiments, Cu top-layer stack had more of an effect on reducing Sn loss compared to Cu2Se top-layer stack.