Enhanced Stability and Performance of α-FAPbI3 Photodetectors via Long-Chain n-Heptanoic Acid Passivation

Owing to its narrow bandgap and excellent thermal stability, formamidinium-lead triiodide (FAPbI₃) is a promising perovskite for high-performance, wide-spectrum photodetectors. Here, we selected long-chain n-heptanoic acid as the passivating agent and introduced it onto the perovskite surface via post-treatment, thereby enabling the fabrication of high-quality α-FAPbI₃ perovskite films and photodetectors. It is found that the carboxylic acid group in the n-heptanoic acid molecule can effectively passivate crystal defects, greatly reduce the density of defect states in the perovskite film, and inhibit the non-radiative recombination of carriers. The α-FAPbI₃ perovskite phase was effectively stabilized. The responsivity of the photodetector optimized by n-heptanoic acid is as high as 0.47 A W^-1 at 740 nm. At the same time, the optimized device still maintains 95% of its initial performance after 552 h of storage in an air environment with a room temperature of 25 °C and a relative humidity of 25%. This method provides a reliable way to prepare a high-performance and stable α-FAPbI₃ photodetector.