Substitution of Zn in Earth‐Abundant Cu2ZnSn(S,Se)4 based thin film solar cells - A status review

Cu2ZnSnS4 (CZTS) and Cu2ZnSn(S,Se)4 (CZTSSe) are the most promising quaternary earth abundant photo-absorber materials for thin film solar cells, with reported power conversion efficiencies (PCE) of more than 12%. In CZTS and CZTSSe based solar cells, similar atomic sizes of Cu and Zn is thought to be the main reason for CuZn and ZnCu antisite defect formation, resulted in severe potential fluctuations and tail states that can be inhibited by an incorporation of alternative bigger atoms such as Cd and Mn. In addition, the large open-circuit voltage deficit observed in CZTS and CZTSe device because of existence of Cu and Zn cation disorder in kesterite crystal. Recently, in the development of CZTS based thin film solar cells the reduction of antisite defects by cation substitution has received considerable attention. This also opens up the possibility to explore materials with similar crystal structures and band gaps as CZTS/CZTSSe such as Cu2XSnS4 (where X = Mn, Cd, Fe, Co, Ni and Ba). In this review, the effect of substituting other metals for Zn is discussed, providing a way to alter defects and tail states in the absorber material of CZTS/CZTSSe thin film solar cells.