A lead-free K2CuBr3 microwires-based humidity sensor realized via QCM for real-time breath monitoring

Halide perovskites have recently emerged as potential humidity-detection materials due to their excellent chemical and physical properties. However, the toxicity of Pb and environmental instability of the lead halide perovskites restrict the application in humidity detection. Herein, a lead-free K2CuBr3 microwires-based quartz crystal microbalance (QCM) humidity sensor was investigated, and the application in human respiratory monitoring was developed. Coupling the high humidity sensitivity of K2CuBr3 with the high mass change sensitivity of QCM, the lead-free K2CuBr3 coated QCM humidity sensor exhibited excellent logarithmic linearity response (R2 = 0.98626, 11–95% RH). In addition, the sensor demonstrated excellent repeatability, fast response/recover time (10.63 s/4.31 s), and considerable stability. Moreover, the Fourier transform infrared spectra (FTIR) and Langmuir adsorption model were applied to reveal the corresponding humidity sensing mechanism. The results indicate the lead-free K2CuBr3-based QCM sensor reported in this work could be a promising candidate for real-time breath monitoring.