Exploration of B-site Alloying in Partially Reducing Pb Toxicity and Regulating Thermodynamic Stability and Electronic Properties of Halide Perovskites

Alloying strategies provide a high degree of freedom for reducing lead toxicity, improving thermodynamic stability, and tuning the optoelectronic properties of ABX3 halide perovskites by varying the alloying element species and their contents. Given the key role of B-site cations in contributing band edge states and modulating structure factors in halide perovskites, the partial replacement of Pb2+ with different B-site metal ions has been proposed. Although several experimental attempts have been made to date, the effect of B-site alloying on the stability and electronic properties of halide perovskites has not been fully explored. Herein, we take cubic CsPbBr3 perovskite as the prototype material and systematically explore the effects of B-site alloying on Pb-containing perovskites. According to the presence or absence of the corresponding perovskite phase, the ten alloying elements investigated are classified into three types (i.e., Type I: Sn, Ge, Ca, Sr; Type II: Cd, Mg, Mn; Type III: Ba, Zn, Cu). Based on the first-principles calculations, we obtain the following conclusions. First, these B-site alloys will exist as disordered solid solutions rather than ordered structures at room temperature throughout the composition space. Second, the alloying of Sn and Ge enhances the thermodynamic stability of the cubic perovskite host, whereas the alloying of the other elements has no remarkable effect on the thermodynamic stability of the cubic perovskite host. Third, the underlying physical mechanism for bandgap tuning can be attributed to the atomic orbital energy mismatch or quantum confinement effect. Fourth, the alloying of different elements demonstrates the diversity in the regulation of crystal structure and electronic properties, indicating potential applications in photovoltaics and self-trapped exciton-based light-emitting applications. Our work provides theoretical guidance for using alloying strategies to reduce lead toxicity, enhance stability, and optimize the electronic properties of halide perovskites to meet the needs of optoelectronic applications.