Printing High-Performance Tungsten Oxide Thin Film Ultraviolet Photodetectors on ZnO Quantum Dot Textured SiO₂ Surface

A zinc oxide quantum dot (ZnO QD) texturing layer was printed on a SiO₂ surface to resolve the issue of ink drop aggregation during inkjet printing tungsten oxide precursor (WO₃Pr) ink, made from ultrasonicating ammonium metatungstate [(NH₃)₆H₂W₁₂O₄₀]in a mixture of Dimethylformamide and water, for high-performance ultraviolet (UV) WO₃ photoconductors. It was found that the ZnO QD textured surface offers a pinning effect of the WO₃Pr ink and hence prevents the ink from aggregating and coagulating into large droplets, which prohibits formation of uniform WO₃Pr films on hydrophobic SiO₂/Si or glass substrates. With the ZnO QD texturing layer, a uniform WO₃ film can be obtained when printing WO₃Pr at room-temperature (22 °C), which reduced cracks and eliminated the coffee ring effect that arises when printing at elevated temperature such as 50 °C. High crystallinity was confirmed on the printed WO₃ films, which leads to UV photoresponsivity up to 16.6 mA/W, which is comparable with the best reported on printed WO₃ UV detectors without a ZnO QD texturing layer. This result shows surface texturing using a pre-printed QD layer provides a facile and compatible approach in controlling inkjet printing for high-quality oxide films directly from precursor solutions.