Room-Temperature NO₂ Gas Sensor Based on Cs₂TeI₆ Thin Film Under Blue-Light Illumination

In the field of gas sensors, halide perovskites have emerged as promising materials for room-temperature sensors. Their potential for development is huge, however due to their instability when exposed to ambient air and the toxicity of Pb, the practical studies are still limited. In this study, a thin film of Cs₂TeI₆, an all-inorganic Pb-free double perovskite, with a thickness of 1.27 mm was prepared on a glass substrate via a non-solution process. The characteristics of the material such as phase structure, morphology, optical absorption and composition of the elements on the surface were studied. They will provide useful data for further studies of this material. The gas-sensing properties of the Cs₂TeI₆-basedsensor were investigated at 25°C using various gases under illumination of a blue 450-nm laser. Under the blue-light illumination, the sensor exhibited good selectivity toward NO₂ gas, with a very low limit of detection of 25 ppb and responsivity of 4.4% toward 1 ppm NO₂. The NO₂-sensing mechanism was proposed and discussed in term of a surface depletion model. The effects of light intensity, light wavelength, humidity, and long-term duration on NO₂-sensing performances were further studied. It showed the maximum responsivity of 18.3% at 52% RH and the long-term stability of 6 weeks. All results indicate that Cs₂TeI₆ is a promising material using for NO₂ gas sensors at RT.