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三氧化钨(WO3)是一种典型的电致变色材料, 因其出色的光-电特性成为科学研究和工程应用的热点材料. WO3的电致变色性能受其氧空位浓度和分布的影响, 进而调控其变色效率和稳定性. 现有调控方法多为以退火为代表的高温处理, 无法维持薄膜的低结晶度, 因而导致循环性能下降. 本研究采用等离子体处理技术调控WO3薄膜氧空位的生成和分布, 采用X射线衍射、扫描电子显微镜、光电测试和循环伏安法等对处理后薄膜进行表征, 确定其微观结构和氧空位水平, 获得氧空位对电致变色性能的调控规律, 并与氩气环境退火所得薄膜进行对比. 结果表明, 等离子体处理能够显著地提高WO3薄膜的表面氧空位浓度, 并在薄膜深度方向形成梯度氧空位分布. 与原始薄膜和氩气退火制备的薄膜相比, 等离子体处理优化后的氧空位分布显著地增强了WO3薄膜的电子注入和抽出能力, 薄膜光学调制范围提升至85%, 且具有更快的变色响应速度和更好的循环稳定性.In recent years, electrochromic materials have been extensively utilized in smart windows, displays, and dimmable devices. WO3, as a typical electrochromic material has received significant attention. Existing researches indicate that the concentration and distribution of oxygen vacancies in WO3 are both important in determining electrochromic effect. However, it has been reported that traditional preparation methods such as annealing can significantly reduce the ability to modulate the crystallinity and optical performance. Hence, proposing a novel approach to enhance the electrochromic properties of WO3 films holds important research significance and application prospects. In this work, the electrochromic properties of WO3 thin films are enhanced by increasing the oxygen vacancy concentration and forming its gradient distribution on the surface through plasma treatment. Firstly, the oxygen vacancy concentration and distribution of the film are optimized by regulating the power and duration of the plasma treatment. Secondly, the structure and optical properties of the plasma treated WO3 films are analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-Vis spectroscopy. Finally, the stability and response speed of each film during the electrochromic cycle are evaluated via electrochemical tests. Through plasma treatment, the concentrations of oxygen vacancies on the surfaces of WO3 films are all significantly increased, and a gradient distribution is formed, which is conducive to enhancing the ability to inject and extract electrons. The treated WO3 films demonstrate better electrochemical stability and chromic stability during the electrochromic cycle, and their transparencies and electrochromic response speeds are also significantly enhanced. Additionally, by increasing the concentration of oxygen vacancies through plasma treatment, the band gap of the film decreases and the electrical conductivity increases, which further validates the effectiveness of modulating concentration of oxygen vacancies on the electrical conductivity of WO3 film. Overall, these results indicate that plasma treatment is an emerging method of significantly improving the electrochromic properties of WO3 films.
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Keywords:
- WO3 /
- oxygen vacancy /
- plasma /
- electrochromism
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图 2 (a) WO3和(b)缺氧WO3的能带结构以及(c)总态密度
Fig. 2. (a) Band structure of WO3 and (b) anoxic WO3 and (c) total state density.
图 4 (a)不同处理前后的WO3薄膜XRD测试结果; (b)不同等离子体处理时长前后的WO3薄膜XRD测试结果
Fig. 4. (a) XRD results of WO3 films before and after different treatments; (b) XRD results of WO3 films before and after different plasma treatment times.
图 5 不同处理前后的WO3薄膜拉曼光谱测试结果
Fig. 5. Raman spectrum test results of WO3 films before and after different treatments.
图 7 不同处理前后的 (a) W 4f和(b) O 1s高分辨率XPS光谱; (c)不同处理前后W 4f高分辨率XPS光谱的拟合分峰结果
Fig. 7. (a) W 4f and (b) O 1s high-resolution XPS spectra before and after different treatments; (c) fitting peak-splitting results of W 4f high-resolution XPS spectra before and after different treatments.
图 8 不同处理前后的WO3薄膜 (a) XPS和表面EDS 原子比; (b) 薄膜深度方向原子比
Fig. 8. WO3 films before and after different treatment: (a) XPS and surface EDS atomic ratio; (b) film depth direction atomic ratio.
图 9 等离子体处理前后的WO3薄膜的(a)透过率光谱和(b)带隙能量图
Fig. 9. (a) Transmittance spectrum and (b) bandgap energy diagram of WO3 thin films before and after plasma treatment.
图 10 (a)原始状态、(b)退火处理后和(c)等离子体处理后WO3薄膜不同电位范围的CV测试和注入和抽出电荷数量
Fig. 10. CV tests and charge quantities inserted and extracted for (a) initial preparation, (b) after annealing and (c) after plasma treatment of WO3 films at different potential ranges.
图 11 (a)原始状态、(b)退火处理后和(c)等离子体处理后WO3薄膜的CV测试和实时光谱透过率以及施加不同电压后的薄膜照片; (d)原始状态、(e)退火处理后和(f)等离子体处理后WO3薄膜在–1.0和+2.0 V电势下30s的电流密度变化(黑色曲线)、透光率变化(红色曲线)以及在有色和漂白状态之间的切换时间特性
Fig. 11. CV test and real-time spectral transmittance of WO3 films at (a) initial preparation, (b) annealing and (c) plasma treatment, and photographs of films at different voltages; (d) changes in current density (black curve), transmittance (red curve) and switching time between colored and bleached WO3 films at -1.0 V and + 2.0 V potentials for 30s after initial preparation, (e) annealing and (f) plasma treatment.
图 12 (a)原始状态、(b)退火处理后和(c)等离子体处理后WO3薄膜的长时CV测试; (d)原始状态、(e)退火处理后和(f)等离子体处理后WO3薄膜的长时透过率测试
Fig. 12. Long-term CV tests of WO3 films (a) in their original state, (b) after annealing and (c) after plasma treatment; long term transmittance tests of WO3 films (d) in their original state, (e) after annealing, and (f) after plasma treatment.
表 1 不同处理工艺方案的四探针电导率测试结果
Table 1. Results of four-probe conductivity tests for various treatment schemes.
样品处理方式 电导率/(10–3 S·m–1) 原始状态 8.27 退火处理 25.30 等离子体处理 10.80 
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表 2 不同等离子体处理工艺方案设计及测试结果
Table 2. Design and test results of different plasma treatment processes.
等离子体放
电功率/W改性时间/min O/W原子比 光学透过率/% 5 10 2.86 84.5 10 20 2.75 81.1 20 30 2.58 74.2 5 20 2.83 82.8 10 30 2.71 78.4 20 10 2.68 79.7 5 30 2.80 80.6 10 10 2.79 83.2 20 20 2.63 76.3
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