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

Guanguang Zhang; Kuankuan Lu; Xiaochen Zhang; Weijian Yuan; Muyang Shi; Honglong Ning; Ruiqiang Tao; Xianzhe Liu; Rihui Yao; Junbiao Peng

doi:10.3390/mi9080377

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

Micromachines (Basel). 2018 Jul 30;9(8):377. doi: 10.3390/mi9080377.

Authors

Guanguang Zhang¹, Kuankuan Lu², Xiaochen Zhang³, Weijian Yuan⁴, Muyang Shi⁵, Honglong Ning⁶, Ruiqiang Tao⁷, Xianzhe Liu⁸, Rihui Yao⁹, Junbiao Peng¹⁰

Affiliations

¹ Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China. msgg-zhang@mail.scut.edu.cn.
² Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China. mskk-lu@mail.scut.edu.cn.
³ Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China. mszhang_xc@mail.scut.edu.cn.
⁴ Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China. 201430320366@mail.scut.edu.cn.
⁵ Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China. 201430320229@mail.scut.edu.cn.
⁶ Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China. ninghl@scut.edu.cn.
⁷ Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China. 201510102158@mail.scut.edu.cn.
⁸ Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China. msliuxianzhe@mail.scut.edu.cn.
⁹ Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China. yaorihui@scut.edu.cn.
¹⁰ Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China. psjbpeng@scut.edu.cn.

Abstract

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.

Keywords: annealing temperature; electrochromism; optical band gap; tungsten trioxide film.

Abstract

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