Optimization of GLAD Angle for E-Beam-Fabricated Tungsten Oxide (WO3) Thin Films Towards Novel Electrochromic Behavior

It is hypothesized that increasing the glancing angle deposition (GLAD) will increase the porosity of WO 3 thin film, thus allowing for better ion diffusion. However, beyond a certain GLAD angle, the film follows a reverse trend and grows quite dense, which is attributable to the highly inclined columnar structure. Consequently, finding an optimal GLAD angle that can produce a perfect porous WO 3 film under the given experimental conditions is critical. In this context, WO 3 thin films, each 400 nm thick, are fabricated using e-beam evaporation at GLAD angle α = 0° (planar), 30°, 55°, 65°, 70° and 80° on fluorine-doped tin oxide (FTO)-coated substrates and Corning glass substrates. The crystalline structure, surface morphology, optical, electrochemical and electrochromic characteristics of the WO 3 thin films are all investigated in detail. Film fabricated at a GLAD angle of 65° showed optimal optical transmittance of 75%, band gap of 3.25 eV, highest coloration efficiency (CE) of 31.06 cm 2 /C and highest diffusion coefficient ( D ) of 7.215 × 10 –4 cm 2 /s. In conclusion, it may be inferred that the optimal GLAD angle under the current experimental conditions is 65°, which could give an ideally porous WO 3 film with novel electrochromic behavior. Graphical Abstract