Flexible NO2 sensors based on WSe2 nanosheets with bifunctional selectivity and superior sensitivity under UV activation

Atomically thin layers of transition metal dichalcogenides (TMDs) have attracted numerous attentions for innovative sensor application. However, the sensing capability of WSe2-based sensors such as the modulation of the selectivity and sensitivity are still to be optimized. Herein, we report a highly selective and flexible gas sensor based on exfoliated WSe2 nanosheets for detection of trace concentration NO2 under ultraviolet (UV) activation at room temperature (25 degrees C). The high quality few-layer WSe2 nanosheets are prepared via a simple liquid-phase exfoliation method, and their structure and electrical properties have been comprehensively investigated by various characterizations and gas sensing measurements. Results reveal that the WSe2 nanosheets-based sensor exhibits a bifunctional selectivity, showing high sensitivity to triethylamine without UV illumination and NO2 under UV illumination. Remarkably, an ultralow limit of detection (LOD) of 8 ppb is registered for NO2 detection under UV. Moreover, the gas sensor demonstrates robust flexibility and bendability without altering the sensor response. This work sheds some light on the integration of WSe2 nanosheets into flexible sensor devices with optimized detection performances.