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Effects of Annealing Temperature on Optical Band Gap of Sol-gel Tungsten Trioxide Films

Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China
Authors to whom correspondence should be addressed.
Micromachines 2018, 9(8), 377;
Received: 6 July 2018 / Revised: 24 July 2018 / Accepted: 25 July 2018 / Published: 30 July 2018
(This article belongs to the Special Issue Wide Bandgap Semiconductor Based Micro/Nano Devices)
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Tungsten trioxide (WO3) is a wide band gap semiconductor material that is used as an important electrochromic layer in electrochromic devices. In this work, the effects of the annealing temperature on the optical band gap of sol-gel WO3 films were investigated. X-ray Diffraction (XRD) showed that WO3 films were amorphous after being annealed at 100 °C, 200 °C and 300 °C, respectively, but became crystallized at 400 °C and 500 °C. An atomic force microscope (AFM) showed that the crystalline WO3 films were rougher than the amorphous WO3 films (annealed at 200 °C and 300 °C). An ultraviolet spectrophotometer showed that the optical band gap of the WO3 films decreased from 3.62 eV to 3.30 eV with the increase in the annealing temperature. When the Li+ was injected into WO3 film in the electrochromic reaction, the optical band gap of the WO3 films decreased. The correlation between the optical band gap and the electrical properties of the WO3 films was found in the electrochromic test by analyzing the change in the response time and the current density. The decrease in the optical band gap demonstrates that the conductivity increases with the corresponding increase in the annealing temperature. View Full-Text
Keywords: optical band gap; tungsten trioxide film; annealing temperature; electrochromism optical band gap; tungsten trioxide film; annealing temperature; electrochromism

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Zhang, G.; Lu, K.; Zhang, X.; Yuan, W.; Shi, M.; Ning, H.; Tao, R.; Liu, X.; Yao, R.; Peng, J. Effects of Annealing Temperature on Optical Band Gap of Sol-gel Tungsten Trioxide Films. Micromachines 2018, 9, 377.

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