Enhancing the humidity sensing performance of Cs₃Cu₂Cl₅ crystals by formation of heterostructures with metallic NbS₂ nanosheets

Apart from their outstanding photoelectronic properties, metal halide perovskites have demonstrated reversible stimuli-responsibility toward a variety of different environmental stimulus. Herein, we used a hot-injection method to deposit lead free perovskite Cs₃Cu₂Cl₅ on layered metal chalcogenide NbS₂. The Cs₃Cu₂Cl₅/NbS₂ heterostructures and the pure Cs₃Cu₂Cl₅ crystals were fabricated into humidity sensors based on impedance change. The heterostructures exhibited an ultra-high humidity sensing response of up to 10⁴ when the relative humidity (RH) was changed from 11% to 97%, which was at least one order of magnitude higher than that of the pure Cs₃Cu₂Cl₅ crystals. The enhanced performance of the heterostructures was attributed to the improved film continuity and hydrophilicity, which respectively led to the improved charge/ion conduction and increased water adsorption. In addition, the Cs₃Cu₂Cl₅/NbS₂ heterojunction is ohmic-like, enabling effective charge/ion transfer across the interface. Given the high RH response of the heterostructures, a contactless sensing device was fabricated, targeting for the vapor emitted from a fingertip. Our work demonstrates that heterostructures between metallic 2D materials and metal halide perovskites are promising sensing materials.