LAUSR

Solar‐to‐fuel conversion with organic–inorganic hybrid halide perovskites has attracted growing attention as a result of their excellent optoelectronic properties as well as the low temperature of the solution based fabrication process. However, the most comprehensively developed hybrid perovskite materials are comprised of the toxic metal lead, raising concerns about environmental health threats. Herein, a lead‐free bismuth (Bi)‐based hybrid perovskite showing in situ growth of heterojunctions is successfully developed at the interface of methylammonium bismuth iodide (MA3Bi2I9) and tri(dimethylammonium) hexa‐iodobismuthate (DMA3BiI6) by a facile solvent engineering technique. The air‐stable MA3Bi2I9/DMA3BiI6 perovskite heterostructure with enhanced photoinduced charge separation exhibit outstanding visible‐light‐induced photocatalytic activity for H2 evolution in aqueous hydrogen iodide solution. The powdered MA3Bi2I9/DMA3BiI6 heterostructured composite (BBP‐5) shows a H2 evolution rate of 198.2 µmol h−1 g−1 without the addition of Pt co‐catalysts under 100 mW cm−2 of visible‐light (λ ≥ 420 nm) illumination.