DFT calculations study of structural, electronic, and optical properties of Cu2ZnSn(S1−xSex)4 alloys

As promising solar cell absorb materials, detailed density functional theory calculations of the structural, electronic, and optical properties of Cu2ZnSn(S1−xSex)4 alloys with different crystal structures (including: zincblende-derived kesterite, zincblende-derived stannite, wurtzite-derived kesterite, and wurtzite-derived stannite) over the whole range of Se composition from x = 0 to x = 1 were systematically investigated in the present work. The calculated results revealed that the lattice constants variation of Cu2ZnSn(S1−xSex)4 alloys obey the Vegard's law; and the wurtzite-derived alloys have better alloy solubility and component-uniform compared with zincblende-derived alloys. In the whole range of x, the calculated lattice constants, band gaps, dielectric constants, and refractive index are nearly linear varying with Se compositions. Using the fitting functional relationships, one not only designs suitable Cu2ZnSn(S1−xSex)4 alloys as absorber materials for solar cells, but also determines the composition of Cu2ZnSn(S1−xSex)4 alloys by conventional optical measurements in practice.