Rigid Amine-Induced Pseudo-3 D Lead-Free Bismuth Halide Perovskite with an Improved Band Edge for Visible-Light Absorption

Bismuth organometal halide perovskites have recently been investigated as potential substitutes for lead perovskite solar-cell absorbers because of their lower toxicity. However, the narrowing of the band gap remains a crucial challenge for their practical application. All known Bi-based perovskites have large band gaps, thereby affording weak visible-light absorption. This study concerns a novel, lead-free, pseudo-3 D perovskite optoelectronic material, (MV)BiI₅ (MV²⁺=methyl viologen). The pseudo-3 D metal-halogen perovskite-like structure is constructed by connecting [BiI₅] ²⁺ units via I⋅⋅⋅I contacts. MV, as a rigid organic amine, is located at the center of each parallelepiped to balance the charge and stabilize the structure. (MV)BiI₅ has a narrow band gap of 1.48 eV and a better photoresponse than (MV)BiCl₅ with a 1 D structure. (MV)BiI₅ is the first Bi-based perovskite compound with a band gap energy comparable with (CH₃NH₃)PbI₃, which is encouraging for optoelectronic applications. This research will open a potential pathway for the design of pseudo-3 D Bi-based perovskites with performances comparable with APbX₃ absorbers.