Unlocking Interfacial Interactions of In Situ Grown Multidimensional Bismuth‐Based Perovskite Heterostructures for Photocatalytic Hydrogen Evolution

To combat the energy crisis and environmental pollution, developing renewable energy technology such as hydrogen (H 2 ) production is necessary. The sulfur–iodine thermochemical cycle has high commercial potential in conducting hydrogen iodide (HI) splitting for H 2 generation, but it requires high‐temperature conditions. In comparison, photocatalytic HI splitting of halide perovskites is non‐polluted and low‐cost for H 2 production at room temperature. Herein, an in situ constructed multidimensional bismuth (Bi)‐based 3D/2D EDABiI 5 /MA 3 Bi 2 I 9 perovskite heterojunction is developed first by synergistically integrating dimensionality control with heterostructure engineering. Accordingly, the optimal EDABiI 5 /MA 3 Bi 2 I 9 without any co‐catalysts exhibits the H 2 evolution rate of 213.63 µmol h −1 g −1 under irradiation. Equally importantly, interfacial dynamics of solid/solid and solid/liquid interfaces play a crucial role in photocatalytic performance. Therefore, using temperature‐dependent transient photoluminescence and electrochemical voltammetric techniques, it is confirmed that the exciton transportation of EDABiI 5 /MA 3 Bi 2 I 9 is accelerated by stronger electronic coupling arising from an enhanced overlap of electronic wavefunctions. Moreover, the effective diffusion coefficient and electron transfer rate of EDABiI 5 /MA 3 Bi 2 I 9 demonstrate efficient heterogeneous electron transfer, resulting in improved photocatalytic hydrogen production. Consequently, the in situ formation of perovskite heterostructures studied by a combination of photophysical and electrochemical techniques provides new insights into green hydrogen evolution and interfacial interaction dynamics for commercial applications of solar‐to‐fuel technology.