Solvent-modulated preparation of lead-free Cs3Bi2I9 polycrystalline film for high-performance photodetectors

Lead-free cesium bismuth iodide (Cs₃Bi₂I₉) perovskite exhibits extraordinary optoelectronic properties and attractive potential in various optoelectronic devices, especially the application for photodetectors (PDs). However, most Cs₃Bi₂I₉PDs demonstrated poor detection performance due to the difficulty in obtaining high-quality polycrystalline films. Therefore, it makes sense to modulate the preparation of high-quality Cs₃Bi₂I₉polycrystalline films and expand its applications. Here, a solvent-modulated method combining anti-solvent and precursor engineering has been developed to regulate the crystallization dynamics of Cs₃Bi₂I₉. Anti-solvent treatment is to suppress the asynchronous separation out of CsI and BiI₃due to significant differences in solubility, promoting uniform nucleation and limiting flake-like growth. Precursor engineering is synchronously used to modulate the subsequent nucleation growth dynamics. Due to the synergistic modulation, smooth and compact Cs₃Bi₂I₉polycrystalline films with distinct grains and grain boundaries can be easily obtained. The as-prepared PD exhibits an excellent on/off ratio of 4.26 × 10⁵as well as the detectivity up to 6.49 × 10¹⁰Jones at zero bias. And, the Cs₃Bi₂I₉PD indicates excellent device stability, maintaining about 70% of the original performance after being stored for 400 h in the air without encapsulation.