Covalent Organic Framework-Enhanced Metal Halide Perovskites for Selective and Sensitive Gas Sensing

Solution-processed lead-free halide perovskite gas sensors possess low gas detection limits, offering promising alternatives to traditional metal oxide chemiresistors. However, halide perovskite chemiresistors often suffer from poor selectivity and durability due to a lack of coordinatively unsaturated surface metal ions and their sensitivity to humidity. To address these issues, a general strategy is presented in which the Cs2PdBr6 perovskite surface is coated with covalent organic framework (COF) to provide hybrid sensor materials that are highly sensitive to specific gases and demonstrate excellent stability under real-working conditions. The hybrid chemiresistors demonstrate high sensitivity and controllable selectivity toward NO2 or NH3 gases. Specifically, TAPB-PDA@Cs2PdBr6 achieves a detection limit of 10 ppb for NO2, the lowest value reported for a perovskite-based gas sensor, maintaining its performance after continuous exposure to ambient air for several weeks. In contrast, COF-5@Cs2PdBr6 shows high selectivity to NH3 and has a detection limit of 40 ppb. Structural and spectroscopic characterization combined with mechanistic studies provide molecular-level insights into the outstanding properties of these new hybrid sensor materials, which set a new benchmark in the field, i.e., surpassing the selectivity and sensitivity of conventional halide perovskite sensors.