退火温度对溶胶-凝胶法氧化钨薄膜电致变色性能的影响

Effect of Annealing Temperature on the Electrochromic Properties of Tungsten Oxide Films by Sol-Gel Method

摘要:

电致变色是指在外加电场的作用下电解质中离子嵌入材料中，使得材料本身光学特性发生变化的现象。电致变色材料被用于建筑隔热、装饰、信息显示等场景。氧化钨（WO₃）作为一种被广泛研究的无机电致变色材料，虽其储量丰富，但受制于苛刻的制备工艺，以及透明导电基底的昂贵价格，在光热调控场景中很少大面积使用无机电致变色薄膜。基于此，采用溶胶-凝胶法（Sol-gel），通过改变退火温度制备了结晶态和非晶态的氧化钨（WO₃）薄膜，同时探索了不同退火温度对其电致变色性能的影响。实验结果表明，随着退火温度（200、250、300和350 ℃）的增加，薄膜由非晶态逐渐转变为结晶态，且薄膜内部结构趋于致密化。在退火温度200 ℃下，薄膜呈现出最佳的电致变色性能及良好的反应可逆性，在1 mol?L^-1的AlCl₃溶液中电压为-0.5 V时，薄膜在633 nm处的光学对比度为79%；而在250、300和350 ℃退火温度下，随着薄膜内部结构趋向于致密，当施加正向电压时嵌入的离子无法在短时间内脱离出来，使得薄膜的光学性质难以回复到初始的状态，造成着色褪色响应速度下降，导致光学对比度不同程度的降低，在633 nm处的光学对比度分别为39.1%、23.7%和46.1%。其中，350 ℃退火的样品在光学对比度上呈现差异化，这归因于薄膜结晶，细微的晶界提供了较多的反应位点。本研究提供了一种简易的、低成本的制备WO₃薄膜的方法，为大面积应用电致变色材料提供了理论参考。

Abstract:

Electrochromism is a phenomenon in which the optical properties of a material are altered due to the embedding of ions in an electrolyte when the material is subjected to an applied electric field. This phenomenon can be utilised in a variety of scenarios， including architectural insulation， decoration and information display. Tungsten oxide （WO?）， a widely researched mechanism-free electrochromic material， still exhibits high costs when used in large-scale mechanism-free electrochromic films in photothermal modulation scenarios. This is due to the stringent preparation process requirements and the costly price of the transparent conductive substrate， despite the material being widely available in our country. In this study， tungsten oxide （WO₃） thin films were prepared by sol-gel method， and the crystalline and amorphous states were prepared by changing the annealing temperature， and the electrochromic properties were tested. The experimental results showed that the films gradually changed from amorphous to crystalline state and the internal structure of the films gradually densified with the increase of annealing temperature. At four annealing temperatures （200 ℃， 250 ℃， 300 ℃， 350 ℃）， the films annealed at 200 ℃ showed the best electrochromic properties with good reversibility. The optical contrast at 633 nm was 79% in 1 mol?L^-1 AlCl₃ solution with -0.5 V applied. The other annealing temperature of the films， due to the internal structure of the films tends to be dense， in the application of forward voltage， the embedded ions can not be de-embedded in a short period of time， making it difficult to return to the initial state of the optical properties of the films， the colouring fading response speed decreased； also led to the film in the state of the colouring of the optical contrast has a varying degree of degradation. One of the samples annealed at 350 ℃ showed differentiation in optical contrast， which may be attributed to the crystallization of the film， with fine grain boundaries providing more reaction sites. This study provides a simple and low-cost method to prepare WO₃ thin films and investigates the influence of the electrochromic properties of the films at different sub-treatment temperatures for large area application of electrochromic materials.