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 Cs3Bi2I9 PDs 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 Cs3Bi2I9 polycrystalline 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 BiI3 due 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 Cs3Bi2I9 polycrystalline films with distinct grains and grain boundaries can be easily obtained. The as-prepared PD exhibits an excellent on/off ratio of 4.26 × 105 as well as the detectivity up to 6.49 × 1010 Jones at zero bias. And, the Cs3Bi2I9 PD indicates excellent device stability, maintaining about 70% of the original performance after being stored for 400 h in the air without encapsulation.