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 (CH3 NH3 )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.