Rigid Amine‐Induced Pseudo‐3‐Dimensional Lead‐Free Bismuth‐Halide Perovskite with Improved Band‐Edge for Visible‐Light Absorption

Bismuth organometal halide perovskites have recently been concerned as a potential substitute of the lead perovskite solar-cell absorbers for their less toxicity. However, the narrowing of the band gap remains a crucial challenge in their practical applications, as all known Bi-based perovskites have large band gaps, thereby affording weak visible-light absorption. Here, we present a novel, lead-free, pseudo-3-dimensional (pseudo-3D) perovskite optoelectronic material, (MV)BiI 5 ( 1 ) (MV 2+ = methyl viologen). The pseudo-3D metal-halogen perovskite-like structure is constructed by connecting [BiI 5 ] 2+ units via II contacts. Methyl viologen as a rigid organic amine is located at the center of each parallelepiped to balance the charge and stabilized the structure. Compound 1 shows a narrow band gap of 1.48 eV and a significant photoresponse compared with (MV)BiCl 5 ( 2 ) with 1D structure. (MV)BiI 5 is the first Bi-based perovskite compound to show band gap energy comparable to (CH 3 NH 3 )PbI 3 , which is encouraging for optoelectronic applications. We open a potential pathway for the design of pseudo-3D Bi-based perovskites to compete with APbX 3 absorbers.