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

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 TiO₂/MXene van der Waals heterojunction. By simply spin-coating MXene nanosheets on TiO₂ film, the UV photodetector exhibits significantly enhanced performance, such as ultrahigh responsivity (202.4 A/W), large specific detectivity (1.79 × 10¹⁴ Jones) and outstanding external quantum efficiency (1.02 × 10⁵%), which are three orders of magnitude higher than those of pure TiO₂ 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 TiO₂/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.