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)BiI 5 (MV 2+ =methyl viologen). The pseudo‐3 D metal‐halogen perovskite‐like structure is constructed by connecting [BiI 5 ] 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)BiI 5 has a narrow band gap of 1.48 eV and a better photoresponse than (MV)BiCl 5 with a 1 D structure. (MV)BiI 5 is the first Bi‐based perovskite compound with a band gap energy comparable with (CH 3 NH 3 )PbI 3 , 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 APbX 3 absorbers.