Supersaturation‐Controlled Growth of Monolithically Integrated Lead‐Free Halide Perovskite Single‐Crystalline Thin Film for High‐Sensitivity Photodetectors

Abstract Monolithical integration of the promising optoelectronic material with mature and inexpensive silicon circuitry contributes to simplifying device geometry, enhancing performance, and expanding new functionalities. Herein, a lead‐free halide perovskite Cs 3 Bi 2 I 9 single‐crystalline thin film (SCTF), with thickness ranging from 900 nm to 4.1 µm and aspect ratio up to 1666, is directly integrated on various substrates including Si wafer, through a facile and low‐temperature solution‐processing method. The growth kinetics of the lead‐free halide perovskite SCTF are elucidated by in situ observation, and the solution supersaturation is controlled to reduce the inverse‐temperature crystallization nucleation density and elongate the evaporation growth. The excellent lattice match and band alignment between Si(111) and Cs 3 Bi 2 I 9 (001) facets promote photogenerated charge dissociation and extraction, resulting in boosting the photoelectric sensitivity by 10–200 times compared with photodetectors based on other substrates. More importantly, this silicon‐compatible perovskite SCTF photodetector exhibits a high switching ratio of 3000 and a fast response of 1.5 µs, which are higher than most reported state‐of‐the‐art lead‐free halide perovskite photodetectors. This work not only gives an in‐depth understanding of the perovskite precursor solution chemistry, but also demonstrates the great potential of monolithical integration of lead‐free halide perovskite SCTF with a silicon wafer for high‐performance photodetectors.