Preparation of WO₃ network squares for ultrasensitive photodetectors

Three-dimensional WO₃ network squares have been fabricated on a large scale by a hydrothermal method at 160 °C without any template or surfactant. The characterization of the network squares with X-ray diffraction, scanning electron microscopy, and transmission electron microscopy indicates a single crystalline hexagonal structure with a square of side length up to 20 μm. The influence of pH value on the morphology of the final product has been studied, indicating that more uniform WO₃ network squares can be obtained at pH 1.7. A possible growth mechanism involves the Ostwald ripening, oriented attachment and etching effect. The UV-vis reflection spectrum indicates a band gap of ∼3.2 eV. The photodetector based on a single WO₃ network square shows remarkable photosensitivity under intermittent illumination of the simulated sunlight, which could mainly be attributed to the specific network structure of WO₃ and the Schottky contacts.