Fully Transparent Ultraviolet Photodetector with Ultrahigh Responsivity Enhanced by MXene‐Induced Photogating Effect

Abstract Transparent photodetectors with the optical signal recognition and conversion capabilities are the core component for smart sensors and next‐generation “see‐through” optoelectronics. However, it is usually difficult to have both excellent optical transmittance and photoresponse performance, which hinders the practicality of transparent photodetectors. Herein, a photogating effect enhanced transparent ultraviolet (UV) photodetector is demonstrated based on the TiO 2 /MXene van der Waals heterojunction. By simply spin‐coating MXene nanosheets on TiO 2 film, the UV photodetector exhibits significantly enhanced performance, such as ultrahigh responsivity (202.4 A/W), large specific detectivity (1.79 × 10 14 Jones) and outstanding external quantum efficiency (1.02 × 10 5 %), which are three orders of magnitude higher than those of pure TiO 2 film. Meanwhile, the device exhibits up to 95% transparency in the visible range. Both the experimental results and theory calculations indicate that local Schottky junctions are established at the TiO 2 /MXene interface. These local junctions exert a giant photogating effect under illumination, which can facilitate the separation of photogenerated carriers and improve the photodetection performance. Moreover, the transparent photodetector has been successfully applied in a UV index wireless sensing system. This work demonstrates the ingenious application of MXene in optoelectronics and provides insight into the design of high‐performance transparent photodetectors.