Understanding the Effect of Crystalline Structural Transformation for Lead-Free Inorganic Halide Perovskites

Lead-free inorganic halide perovskites have triggered appealing interests in various energy-related applications including solar cells and photocatalysis. However, why perovskite-structured materials exhibit excellent photoelectric properties and how the unique crystalline structures affect the charge behaviors are still not well elucidated but essentially desired. Herein, taking inorganic halide perovskite Cs₃ Bi₂ Br₉ as a prototype, the significant derivation process of silver atoms incorporation to induce the structural transformation from Cs₃ Bi₂ Br₉ to Cs₂ AgBiBr₆ , which brings about dramatic differences in photoelectric properties is unraveled. It is demonstrated that the silver incorporation results in the co-operated orbitals hybridization, which makes the electronic distributions in conduction and valence bands of Cs₂ AgBiBr₆ more dispersible, eliminating the strong localization of electron-hole pairs. As consequences of the electronic structures derivation, exhilarating changes in photoelectric properties like band structure, exciton binding energy, and charge carrier dynamics are verified experimentally and theoretically. Using photocatalytic hydrogen evolution activity under visible light as a typical evaluation, such crystalline structure transformation contributes to a more than 100-fold enhancement in photocatalytic performances compared with pristine Cs₃ Bi₂ Br₉ , verifying the significant effect of structural derivations on the exhibited performances. The findings will provide evidences for understanding the origin of photoelectric properties for perovskites semiconductors in solar energy conversion.