A theoretical study on absorbers for the intermediate band solar cell from group-IV element (Si, Ge, Sn) doped AgGaS2

Chalcopyrite compounds are employed as host materials for intermediate band solar cells owing to the wide band gaps and excellent optical properties. In this study, we focus on the chalcopyrite AgGaS₂ as a potential host for intermediate band solar cell. To identify an ideal absorber for an intermediate band solar cell, the structural stability, electronic structure, and the possibility of achieving of the large doping concentration are investigated on group-IV element (Si, Ge, Sn) doped AgGaS₂ using the first-principles calculations. Based on the ab-initio molecular dynamic simulation and the calculations on the phonon spectrum, the doped samples exhibited strong dynamic stabilities and thermodynamic stabilities. The calculations on electronic structures indicate that Ge and Sn doped at Ga site can form isolated and partially filled intermediate bands in AgGaS₂, whereas Si doped at Ga site cannot. In addition, the feasibility of large doping concentration is investigated, and the results show that the lowest defect formation energy is obtained for Sn doping at Ga site under Ag-poor, Ga-poor and S-rich conditions. Overall, our theoretical work suggested that Sn doped AgGaS₂ is an ideal absorber for the intermediate band solar cell.