Effect of Pre-annealing on the Formation of Cu2ZnSn(S,Se)4 Thin Films from a Se-containing Cu/SnSe2/ZnSe2 Precursor

Abstract

A Se-containing Cu/SnSe2/ZnSe precursor was employed to introduce S to the precursor to form Cu2ZnSn(S,Se)4 (CZTSSe) film. The morphology of CZTSSe films strongly varied with two different pre-annealing environments: S and N2. The CZTSSe film with S pre-annealing showed a dense morphology with a smooth surface, while that with N2 pre-annealing showed a porous film with a plate-shaped grains on the surface. CuS and Cu2Sn(S,Se)3 phases formed during the S pre-annealing stage, while SnSe and Cu2SnSe3 phases formed during the N2 pre-annealing stage. The SnSe phase formed during N2 pre-annealing generated SnS2 phase that had plate shape and severely aggravated the morphology of CZTSSe film. The power conversion efficiency of the CZTSSe solar cell with S pre-annealing was low (1.9%) due to existence of Zn(S.Se) layer between CZTSSe and Mo substrate. The results indicated that S pre-annealing of the precursor was a promising method to achieve a good morphology for large area application.