2022 Volume 91 Issue 6 Pages 327-333
Ternary and multinary compounds used in polycrystalline thin-film solar cells are I-III-VI2 semiconductors typified by CuInSe2 (CISe), I2-II-IV-VI4 compounds such as Cu2ZnSnS4 (CZTS),and I2-IV-VI3 compounds such as Cu2SnS3 (CTS). Their crystal structures are chalcopyrite type (space group I42d (122)) for CISe, kesterite type (space group I4 (79)) for CZTS, and monoclinic system (space group Cc (9)) for CTS. In this review, we describe the characteristics of their crystal structures and electronic structures such as band-gap energy and energy levels of valence band maxima (VBM) and conduction band minima (CBM). The differences of electronic structures between ZnSe and CuGaSe2, CuInSe2 and Cu2ZnSnSe4, and Cu2ZnSnS4 and Cu2SnS3 will be discussed on the basis of the results of theoretical calculations and molecular orbital energy-level diagrams.