Solution-Based Preparation of Cu2ZnSn(S,Se)4 for Solar Cells—Comparison of SnSe2 and Elemental Se as Chalcogen Source

Thin-film solar cells with a Cu
₂
ZnSn(S,Se)
₄
absorber were prepared in a two-step process based on a metal salt solution that is deposited onto a molybdenum-coated substrate and subsequently annealed in a selenium-containing nitrogen atmosphere. The solar cell performance could be improved to efficiencies above 10% without usage of the highly toxic hydrazine or H
₂
Se gas. A crucial step for obtaining high-quality absorbers is the incorporation of Se during the annealing process. Therefore, a detailed investigation of elemental Se and SnSe
₂
as chalcogen sources with various process parameters was performed. SnSe
₂
resulted in absorbers with improved morphology but could achieve only medium efficiencies, whereas elemental Se forms a triple-layer structure with efficiencies of up to 10.3%.