First principles calculation of the electronic-optical properties of Cu 2 MgSn(S x Se 1− x ) 4

Based on the density functional theory with hybrid functional approach, we calculated the structural, electronic, and the optical properties of Cu 2 MgSn(S 1- x Se x ) 4 (CMTSSe), an potential photovoltaic material for thin film solar cells. The calculation reveals a phase transition from kesterite to stannite structure when Zn atoms are substituted by Mg atoms. In particular, the S-to-Se ratio can determine the energy splitting between the electronic states at the top of the valence band. The band gaps of CMTSSe can be tuned in the ranges of 1.01-1.58 eV. Calculated optical properties and tunable band gaps make them beneficial for achieving band-gap-graded solar cells.