Air-processed Cs3Bi2I9 polycrystalline film and self-powered photodetector

As a prototypical bismuth-based perovskite material, Cs 3 Bi 2 I 9 exhibits notable advantages including low toxicity and excellent environmental stability, rendering it a highly promising candidate for optoelectronic applications. However, the precise crystallization control of Cs 3 Bi 2 I 9 polycrystalline films remains challenging, characterized by rapid crystallization, poor film morphology, and a heavy dependence on inert atmospheres during fabrication. The presence of ambient moisture severely degrades the crystallinity and morphology of the films, making the high-quality fabrication of polycrystalline films in air a critical challenge to overcome. Herein, we investigated how ambient humidity influences the crystallization and morphology of Cs 3 Bi 2 I 9 . It was found that the presence of atmospheric moisture severely induces a flake-island growth of Cs 3 Bi 2 I 9 polycrystalline films, ultimately leading to a porous and discontinuous film morphology. Meanwhile, we proposed a synergistic preheating strategy to regulate the crystallization of air-processed Cs 3 Bi 2 I 9 . By synchronously preheating both the substrate and the precursor solution, a thermal solvent barrier can be established. This barrier mitigated the detrimental effect of moisture on crystallization during the spin-coating process, thereby markedly suppressing the flake-island growth and yielding compact Cs 3 Bi 2 I 9 polycrystalline films. Furthermore, we established the optimal preheating temperature windows under various ambient humidity conditions. Self-powered photodetectors were subsequently fabricated based on the optimized polycrystalline thin films, which exhibited favorable photoresponse performance.