Theoretical Design of Inorganic Flexible Bulk Photovoltaic Materials.

Current flexible photovoltaics (PVs) are usually based on low-dimensional structures of inorganic semiconductors and hybrid perovskites, as well as organic materials. Here, we propose a type of inorganic flexible bulk PV material, evaluating its structure flexibility, electronic structure, and PV efficiency in the framework of density functional theory, suggesting α-Ag2S as the best candidate. It is found that the band structure and effective masses of α-Ag2S can be significantly modulated by external strain, whereas leaving the high PV efficiency was not affected much. The flexibility of α-Ag2S can be further enhanced by applying electron doping during stretching or applying hole doping during compression. We further studied the intrinsic defect properties of α-Ag2S by using the Heyd-Scuseria-Ernzerhof hybrid functional, and the calculation results show that α-Ag2S is a defect-tolerant semiconductor even when an external strain is applied. Our results open the door for searching inorganic flexible bulk PV materials for robust flexible solar cells.