A new family of inorganic double perovskite oxides containing bismuth for photovoltaic applications*

Recently, halide double perovskites containing bismuth, such as Cs₂AgBiBr₆, have emerged as benign and promising alternatives to lead-organohalide perovskite photovoltaics. However, these halide double perovskites have large indirect band gaps and degrade over a period of weeks on exposure to ambient air and light. We use regression analysis and high-throughput density-functional theory (DFT) calculations to explore the vast composition space of double perovskite oxides containing bismuth to identify promising photovoltaics. We predict a stable family of compounds with a general formula of A'A"TeBiO₆, where A' and A" are alkali and alkaline-earth metal cations respectively. We predict an indirect band gap of 1.94 eV and 1.99 eV for KBaTeBiO₆ and RbBaTeBiO₆, respectively, which is similar to that of Cs₂AgBiBr₆ (2.06 eV). The effective mass of holes and electrons for KBaTeBiO₆ is 0.25m_e and 0.28m_e, respectively, which is comparable to those (0.14m_e and 0.37m_e) for Cs₂AgBiBr₆. We have successfully synthesized KBaTeBiO₆ using wet-chemistry synthesis, with preliminary UV-vis measurements showing an indirect band gap of 1.7 eV. We will discuss the effect of composition on the electronic structure of these double perovskites.