摘要： NO2 sensors with ultrahigh sensitivity are demanded for future electronic sensing systems. However, traditional sensors are considerably limited by the relative low sensitivity, high cost and complicated process. Here, we report a simply and reliable flexible NO2 sensor based on single-layer MoS2. The flexible sensor exhibits high sensitivity to NO2 gas due to ultra-large specific surface area and the nature of two-dimensional (2D) semiconductor. When the NO2 is 400 ppb (parts per billion), compared with the dark and strain-free conditions, the sensitivity of the single-layer sensor is enhanced to 671% with a 625 nm red light-emitting diode (LED) illumination of 4 mW/cm2 power under 0.67% tensile strain. More important, the response time is dramatically reduced to ～16 s and it only needs ～65 s to complete 90% recovery. A theoretical model is proposed to discuss the microscopic mechanisms. We find that the remarkable sensing characteristics are the result of coupling among piezoelectricity, photoeletricity and adsorption-desorption induced charges transfer in the single-layer MoS2 Schottky junction based device. Our work opens up the way to further enhancements in the sensitivity of gas sensor based on single-layer MoS2 by introducing photogating and piezo-phototronic effects in mesoscopic systems.