Halide-dependent humidity sensing of Cs2SnX6 (X = Cl, Br, I) perovskites for real-time human physiological moisture detection

Abstract

Halide perovskites (HPs) have received increasing attention in the last two decades due to unique component diversity and structural tunability, although additional efforts are necessary for HPs beyond photovoltaic and light-emitting domains, e.g. gas/humidity sensing. Here, all-inorganic lead-free HPs Cs₂SnX₆ (X = Cl, Br, I) were synthesized by simple room-temperature precipitation without any surfactant or organic solution. Afterwards, Cs₂SnX₆ HPs were systematically investigated in terms of structure, morphology, energy band and surface state. Explored as humidity sensing materials, Cs₂SnX₆ exhibit favorable humidity sensing performance with a response sequence of Cs₂SnCl₆ > Cs₂SnBr₆ > Cs₂SnI₆. Remarkably, the Cs₂SnCl₆ sensor achieves a long-term stability at 11–97% relative humidity (RH) and a high response value of 4 orders of magnitude (3.6 × 10⁴) with a short response time (15 s). Furthermore, the precise humidity detection capability makes the Cs₂SnCl₆ sensor extremely promising for real-time, non-contact human breath and finger monitoring. Ultimately, complex impedance spectra at various RH levels provide an explanation for the humidity sensing mechanism. In addition to offering an optional material for humidity sensors, this work offers fresh perspectives on next-generation sensory devices that use lead-free HPs to detect physiological aspects of human health.