Flexible and transparent sensors for ultra-low NO2 detection at room temperature under visible light illumination

Abstract

Metal oxide based gas sensors should mostly work at high temperatures; the high working temperature is associated with safety concerns and high energy consumption, which makes portable and wearable devices almost impossible, and the inhomogeneous temperature distribution over a sensor also has a detrimental effect on the device performance. However, all the above problems can be effectively resolved by using visible light-excited sensors working at room temperature. By depositing an array of well-aligned In₂O₃ nanowires on polyimide (PI) substrates, we fabricate flexible and transparent sensors that achieve room temperature gas sensing using visible light as the excitation source. The detection limit to NO₂ is as low as 10 ppb under illumination using both monochromatic (blue) and polychromatic (white) light sources. The sensing performance remains consistent after repetitive bending and long-term operation. Remarkably, the sensor exhibits recoverable response to 500 ppb NO₂ even under the illumination of an iPhone screen with a low irradiance of 0.56 W m⁻². Through a systematic study of the interaction between the photoelectric and gas sensing properties of the materials, we also explore the mechanism of photo-induced gas sensing reactions at room temperature. This work will lay the foundation for gas sensors that can be used in portable and wearable devices.