Low-temperature open-atmosphere growth of WO3 thin films with tunable and high-performance photoresponse

Tungsten oxide (WO3), an n-type semiconductor, has many potential applications, e.g., electrochromic devices, photodetectors, photoelectrochemical cells, photocatalysts, supercapacitors, memristors, electrolyte-gated transistors, etc. Most deposition routes of films require either vacuum processes or post-deposition annealing, which is not suitable for many applications. In this work, WO3 thin films are made from a W[CO]6 precursor using atmospheric pressure-spatial chemical vapor deposition (AP-SCVD), without any post-deposition annealing. Films were grown on Si substrates at 320 °C and were conformal over cm2 areas, with the film-preferred orientations tuned via control of growth rate. Three exemplar photo-responsive functions with strong performance are demonstrated: water oxidation, UV photodetection, and photocatalytic degradation. The strong performance is linked to the highly exothermic reaction which produces crystalline materials at a low deposition temperature as well as control of the film orientation through tuning the film growth rate. Overall, AP-SCVD is shown to have key advantages over other routes for forming WO3 thin films for photo-responsive applications.