Improvement of hetero-interface engineering by partial substitution of Zn in Cu₂ZnSnS₄-based solar cells

Abstract

This paper investigates the effects of partial substitution of zinc (Zn) in pure sulfide kesterite (Cu2ZnSnS4) by cadmium (Cd) and manganese (Mn) incorporation. Thin films of Cu2ZnSnS4 (CZTS), Cu2Zn1–xCdxSnS4 (CCZTS) and Cu2Zn1–xMnxSnS4(CMZTS) were produced chemically. A comparison of pure CZTS with CCZTS and CMZTS was performed to study the influence of Cd and Mn incorporation on the morphology, structure, optical and electronic properties of the films. The results show an improvement of the morphology and an adjustment of the band gap and valence band position by partial substitution of Zn with Cd and Mn. In addition, for the first time, the band alignment at the absorber/buffer hetero-interface is studied with partial Zn substitution. Band alignments at the absorber/buffer hetero-interface were estimated by XPS and UV/Visible measurements. The results show a cliff-like CBO for CZTS/CdS heterojunction, a spike-like CBO for CCZTS/CdS and a near flat-band CBO for CMZTS/CdS heterojunction.