Cs<sub>3</sub>Bi<sub>2</sub>Cl<sub>3</sub>Br<sub>6</sub>:g‑C<sub>3</sub>N<sub>4</sub> Nanostructure-Based Thin Film\nPhotocatalysts for Hydrogen Production under Daylight and Sim

The\nstrategic design of nanocomposites and their rationally constructed\nheterojunctions offer an effective approach for enhancing light harvesting\nand optimizing energy conversions. Herein, we report the design and\nsynthesis of an aqueous-stable, lead-free Cs<sub>3</sub>Bi<sub>2</sub>Cl<sub>3</sub>Br<sub>6</sub> perovskite integrated with g-C<sub>3</sub>N<sub>4</sub>. An excellent band alignment of Cs–Bi-based\nperovskite with g-C<sub>3</sub>N<sub>4</sub> was achieved by tuning\nthe anion in the Cs–Bi-based perovskite, leading to remarkable\nphotocatalytic performance. The construction of a hybrid nanocomposite\nin a thin film device achieved an impressive photocatalytic hydrogen\ngeneration rate of 341 μmol h<sup>–1</sup> g<sup>–1</sup>, which is 16 times higher than that of the perovskite@g-C<sub>3</sub>N<sub>4</sub> in powder form. The test results are albeit higher\nwhen a quartz reactor is used, where 20 mg of the optimized catalyst\nreaches up to 539 μmol g<sup>–1</sup> h<sup>–1</sup> with an apparent quantum efficiency (AQE) of 1.32%. Spectroscopic\nstudies, including photoluminescence (PL) and time-correlated single\nphoton counting (TCSPC), have established the presence of a long-lived\ncharge-separated state and confirmed excited state electron injection\ninto g-C<sub>3</sub>N<sub>4</sub>. Cs<sub>3</sub>Bi<sub>2</sub>Cl<sub>3</sub>Br<sub>6</sub>@g-C<sub>3</sub>N<sub>4</sub> heterojunctions\nnot only accelerate charge transfer but also significantly enhance\nthe hydrogen evolution rate and stability of the photocatalysts.