Evaporation-Driven Deposition of WO₃ Thin Films from Organic-Additive-Free Aqueous Solutions by Low-Speed Dip Coating and Their Photoelectrochemical Properties

Abstract

We prepared tungsten trioxide (WO3) photoelectrode films from organic-additive-free aqueous solutions by a low-speed dip-coating technique. The evaporation-driven deposition of the solutes occurred at the meniscus during low-speed dip coating, resulting in the formation of coating layer on the substrate. Homogeneous WO3 precursor films were obtained from (NH4)10W12O41·5H2O aqueous solutions and found to be crystallized to monoclinic WO3 films by the heat treatment at 400-700 °C. All the films showed a photoanodic response irrespective of the heat treatment temperature, where a good photoelectrochemical stability was observed for those heated over 500 °C. The highest photoanodic performance was observed for the WO3 film heated at 700 °C, where the IPCE (incident photon-to-current efficiency) was 36.2% and 4.6% at 300 and 400 nm, respectively.

Aqueous synthesis of tin- and indium-doped WO3 films via evaporation-driven deposition and their electrochromic properties

“…1). [29][30][31] The evaporation-induced concentration enabled us to make homogeneous WO 3 coating layers even from low-concentration solutions. Moreover, in this process, Sn-or In-doping was easily succeeded by the addition of tin or indium salts into the coating solutions.…”

“…We recently suggested a low-speed dip-coating technique as a novel coating technique for making metal oxide thin lms from organicadditive-free aqueous solutions. [29][30][31] Fig. 1 shows a schematic illustration of the lm deposition during low-speed dip coating.…”

Oxygen Vacancy-Enhanced Photoelectrochemical Water Splitting of WO3/NiFe-Layered Double Hydroxide Photoanodes

“…Photoelectrochemical (PEC) device for direct water splitting to hydrogen is highly desirable for the increasing demand of renewable energy. − Until now, various photoanodes are explored for PEC water splitting, including TiO 2 , ZnO, BiVO 4 , WO 3 , and hematite (α-Fe 2 O 3 ). − Among them, WO 3 is considered as a promising candidate due to the suitable band gap (∼2.7 eV), elemental abundance, and nontoxicity. − Nevertheless, pure WO 3 photoanodes still suffer from intrinsic drawbacks, such as the serious recombination of photogenerated carriers and gradual loss of photoactivity. , …”

Evaporation-Driven Deposition of ITO Thin Films from Aqueous Solutions with Low-Speed Dip-Coating Technique

“…However, the high surface tension of water (72 mN m –1 ) provides a poor wettability of many substrates such as glasses, ceramics, and metals, inhibiting the homogeneous film formation from aqueous coating solutions. Recently, a low-speed dip-coating technique has been suggested for making metal oxide thin films from metal salt aqueous solutions. − The schematic illustration of the film deposition during low-speed dip coating is shown in Figure . When the substrate withdrawal speed of dip coating is fully low (below 1.0 cm min –1 ), the evaporation of solvents from the coating layer becomes faster than the motion of the substrates.…”

“…The coating process accompanied by the evaporation-driven deposition of solutes would hinder the aqueous solution from gathering together to form droplets, achieving the homogeneous deposition of a film on the substrate. Previously, we succeeded in preparing SnO 2 , TiO 2 , and WO 3 thin films from SnCl 4 , TiOSO 4 , and (NH 4 ) 10 W 12 O 41 aqueous solutions, respectively, by low-speed dip coating, where any other additives were not used for modifying the wettability of the coating solutions. The novel dip-coating technique enables the fabrication of metal oxide thin films from simple solutions containing only metal salts and water with common and inexpensive equipment, providing a low-cost coating process.…”