Influence of Cu2S, SnS and Cu2ZnSnSe4 on optical properties of Cu2ZnSnS4

We have studied influence of Cu2ZnSnSe4 (CZTSe) and secondary phases of Cu2S and SnS on optical properties of kesterite-type Cu2ZnSnS4 (CZTS) by using the effective medium theory. We found that CZTSe and Cu2S cause band gap reduction and enhance light absorption of CZTS at all photon energies of the sunlight whereas SnS changes optical properties of CZTS only at large photon energies beyond the solar spectrum. Optical spectra of CZTS(Se) has been studied by first principles calculations within hybrid functional that was used as input for the effective medium theory.