Theoretical assessment of antiperovskite oxyhalides Rb3OX (X = Br, I) as promising photovoltaic materials

Antiperovskite oxyhalides A 3 OX (A = alkali metal; X = halide anion) exhibit high structural symmetry and electronic dimensionality, which are expected to hold excellent photovoltaic properties. To date, an investigation into the photovoltaic performance of antiperovskite oxyhalides still needs to be implemented. In this research, the optoelectronic and photovoltaic performance as well as the mechanical properties of A 3 OX (A = Cs, Rb, K; X = I, Br) have been comprehensively explored. In terms of mechanical and thermodynamic stability, these oxyhalides are both stable. Specifically, the stability of cubic Rb 3 OI is validated with respect to the dynamic and thermal stability. The bandgap engineering can be achieved by virtue of the A-site cation, while the X-site anion contributes little to both band edges. The direct-allowed gaps are 1.53 eV for Rb 3 OBr and 1.63 eV for Rb 3 OI, which makes them viable for solar cells. The visible-light absorption is moderate for Rb 3 OX (X = Br, I) since its highest absorption coefficient is less than 3 × 10 4 cm −1 . Consequently, the maximum efficiency limits are 27.8 % for Rb 3 OBr and 26.5 % for Rb 3 OI at the film thickness of 1.0 μm. Our study unveils that all-inorganic Rb-based oxyhalides can serve as absorber layer materials for solar cells because of their non-toxic components and high-performance. • The optoelectronic properties of A 3 OX (A = K, Rb, Cs; X = Br, I) are studied. • The stability is thoroughly examined for cubic Rb 3 OI. • Rb-based oxyhalides exhibit appropriate direct bandgaps for solar cells. • The simulated maximum efficiencies are 30.3 % for Rb 3 OBr and 28.9 % for Rb 3 OI.