Efficient Direct Band Gap Photovoltaic Material Predicted Via Doping Double Perovskites Cs2AgBiX6 (X = Cl, Br)

• Published in: Journal of physical chemistry. C Vol. 125; no. 20; pp. 10868 - 10875
• Main Authors: Ma, Xinbo, Li, Zhenyu, Yang, Jinlong
• Format: Journal Article
• Language: English
• Published: American Chemical Society 27.05.2021
• Subjects: C: Energy Conversion and Storage
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.1c01871

Double perovskites are proposed as a Pb-free substitution of toxic lead-halide perovskite photovoltaic materials. Unfortunately, they are usually either unstable or have an undesirable electronic structure. In this study, we start from a stable double perovskite, Cs2AgBiX6 (X = Cl, Br), which has a large and indirect band gap. Based on first-principles calculations, we find that a transition from indirect to direct band gap can be realized via doping Sn2+ (Ge2+) with occupied 5s (4s) orbitals. At the same time, the band gap decreases to a value suitable for photovoltaic applications. The optical absorption is largely enhanced, and the exciton binding energy is also significantly reduced upon doping. These effects lead to high power conversion efficiencies. For example, the efficiency of Ge–Te-codoped Cs2AgBiCl6 is 31.4%, which is the highest among all known nontoxic stable halide perovskite materials. The results presented here open a new avenue for photovoltaic material design.