Unraveling the Gas-Sensing Mechanisms of Lead-Free Perovskites Supported on Graphene.

Lead halide perovskites have been attracting great attention due to their outstanding properties and have been utilized for a wide variety of applications. However, the high toxicity of lead promotes an urgent and necessary search for alternative nanomaterials. In this perspective, the emerging lead-free perovskites are an environmentally friendly and harmless option. The present work reports for the first time gas sensors based on lead-free perovskite nanocrystals supported on graphene, which acts as a transducing element owing to its high and efficient carrier transport properties. The use of nanocrystals enables achieving excellent sensitivity toward gas compounds and presents better properties than those of bulky perovskite thin films, owing to their quantum confinement effect and exciton binding energy. Specifically, an industrially scalable, facile, and inexpensive synthesis is proposed to support two different perovskites (Cs 3 CuBr 5 and Cs 2 AgBiBr 6 ) on graphene for effectively detecting a variety of harmful pollutants below the threshold limit values. H 2 and H 2 S gases were detected for the first time by utilizing lead-free perovskites, and ultrasensitive detection of NO 2 was also achieved at room temperature. In addition, the band-gap type, defect tolerance, and electronic surface traps at the nanocrystals were studied in detail for understanding the differences in the sensing performance observed. Finally, a comprehensive sensing mechanism is proposed.