ABX3-type lead-free perovskites using superatom ions with tunable photovoltaic performances

Abstract

Expanding the family of ABX₃-type perovskites is very important for developing excellent photoelectric materials. The perovskite-based H₅O₂⁺ superalkali cation had been explored, but perovskites with stable dynamics performance using superalkali and superhalogen ions are not yet found. In this work, H₅O₂⁺ and BH₄⁻ are introduced into a cubic CsPbI₃ perovskite, and Pb is replaced with Ge and Sn, respectively. Then, cubic H₅O₂MI_x(BH₄)_3−x (M = Ge and Sn; x = 0, 1, 2, and 3) perovskites are systematically studied by employing density functional theory-based first-principles calculations and ab initio molecular dynamics simulations. The calculated results indicated that the perovskites show a wide range of material properties, i.e., stable dynamics performance at normal temperature and pressure, suitable tolerance factors (0.86–1.00), tunable direct band gaps (0.96–3.28 eV), and small effective hole and electron masses (0.17–0.70 m_e). Moreover, a power conversion efficiency over 31% is obtained for single-junction perovskite solar cells based on the cubic H₅O₂GeI₃, H₅O₂SnI₃ and H₅O₂SnI₂BH₄ perovskites. These results indicate that the cubic H₅O₂MI_x(BH₄)_3−x perovskites may be used for fabricating high-performance photoelectric devices, and an intriguing platform can be provided for developing other new stable lead-free superatom perovskites by using superalkali and superhalogen ions.