Interface Nanojunction Engineering of Electron-Depleted Tungsten Oxide Nanoparticles for High-Performance Ultraviolet Photodetection

This work reports a general and facile route, i.e., thermal decomposition of a precursor followed by ultrafast thermal annealing (TDP-UTA), to the in situ fabrication of a nanojunction-interlinked tungsten oxide nanoparticle (WO₃-NP) networks for extraordinary ultraviolet (UV) photodetection. TDP leads a spin-coated ammonium metatungstate thin layer to in situ self-assemble into a highly crystalline WO₃-NP mesoporous film on SiO₂/Si substrates with prepatterned electrodes. The as-synthesized WO₃-NPs have dimensions comparable to the Debye length (≈43 nm), which is critical to the optimal electron-depletion effect for high gain in photodetection. UTA creates the NP-NP interface nanojunctions between neighboring WO₃-NPs, which is the key to high-efficiency electron transport with minimized charge recombination in optoelectronic processes. The photodetectors based on such nanojunction-interlinked WO₃-NP networks exhibit a photocurrent-to-dark-current ratio of 5600, the highest value for any WO_x-based photodetectors ever reported. Moreover, the obtained photoresponsivity is up to 139 A/W (or 27.8 A/W·V) upon 360 nm illumination, which is over 1 order of magnitude higher than that of any previously reported WO_x-nanostructure film photodetectors. These results demonstrate that the TDP-UTA route is a low-cost, robust, and scalable pathway to the in situ fabrication of interlinked semiconducting-nanostructure networks for high-performance optoelectronics and sensors.