Exploring Optical Sensing Mechanisms in Metal Halide Perovskites for Hydrogen Gas Detection

Metal halide perovskites (MHPs) are emerging as promising candidates for gas sensing due to their tunable optoelectronic properties, room temperature operation, and scalable fabrication. In this work, hydrogen (H 2 ) sensing capabilities of methylammonium lead iodide (MAPI) thin films via photoluminescence (PL) spectroscopy is investigated. MAPI films demonstrate a consistent and rapid PL intensity response in a matter of seconds upon exposure to H 2 , characterized by an initial increase followed by a decay below baseline, which recovers in ambient air. This reversible behavior is preserved over multiple cycles over an hour, indicating reusability. The magnitude and duration of the PL response vary with H 2 concentration, demonstrating the sensor's ability to detect not only presence but also quantity of gas. Control experiments using encapsulated films confirm specificity to H 2 , and X‐ray Diffraction (XRD) analysis confirm the interaction does not cause any significant crystallographic changes. Further analysis with thinner films and mixed‐halide compositions suggests that both surface and bulk interactions, as well as defect‐mediated processes, contribute to sensing. This study establishes MAPI as a viable optical sensor for H 2 gas with fast response, sensitivity to concentration, and potential for low‐cost implementation.