Lead-Free Halide Double Perovskite Cs₂AgBiCl₆ for H₂S Trace Detection at Room Temperature

Hydrogen sulfide (H₂S) is an important respiratory biomarker of many diseases, and thus, developing H₂S gas sensors with low detection limits at low operating temperatures is essential for the early diagnosis of diseases in low-resource environments. Although lead halide perovskites have unique electronic and optical properties, the high toxicity of lead has prompted the development of alternative materials. In this study, Cs₂AgBiCl₆ was synthesized using a simple method. The sensor based on Cs₂AgBiCl₆ showed excellent sensing of H₂S gas at room temperature over a wide humidity range, with high response (90.6 vs 10 ppm of H₂S) and fast response speed (99.6 s vs 400 ppb H₂S). The detection limit was low (5 ppb H₂S), and the selectivity at room temperature was excellent. Small changes in H₂S concentration (<100 ppb) were detected as a fully reversible resistance signal. Additionally, sum frequency vibration spectroscopy and DFT calculations showed that the high gas sensitivity was attributed to the physical adsorption of H₂S at Cl vacancies on the surface of Cs₂AgBiCl₆, as well as efficient charge transfer. This work provides an avenue for developing high-performance gas sensors based on nontoxic, wide band gap, halide double perovskite semiconductors operating at room temperature.