Reversible dehydration-hydration process in stable bismuth-based hybrid perovskites

Lead-free hybrid perovskites have attracted significant attention due to the toxicity of lead and poor stability of lead hybrid perovskites. Among them, bismuth-based hybrid perovskites are currently being developed as they possess negligible toxicity, moderate price and great stability. Herein, we report the synthesis of two stable organic-inorganic perovskites based on one-dimensional iodobismuthates and the benzimidazolium cation (BzlmH)(+). Firstly, the BzImH[BiI](4)center dot H2O structure (IEF-4 RT-phase) was prepared using a simple and fast synthetic method at room temperature, leading to the dehydrated BzImH[BiI](4) (IEF-4 HT-phase) upon the removal of water by soft heating. This dehydration-hydration process, which has never been reported for Bi-based perovskites, is fully reversible, affecting the optoelectronic properties of the solid, with an optical bandgap of similar to 2 eV. Furthermore, this perovskite material formed stable and homogeneous thin films, which exhibited a high absorption coefficient (1.5 x 10(5) cm(-1)) comparable to that of the CH3NH3PbI3 lead perovskite. Thus, both the optoelectronic properties and air stability of these perovskites make them suitable as absorber materials in solar cells.