A New Strategy of Nanocompositing Vanadium Dioxied with Excellent Durability

Vanadium dioxide is widely investigated as a thermochromic smart window material. However its mediocre thermochromic property (low solar modulation ability ΔTsol, low luminous transmission Tlum, and high transition temperature (τc)) and thermodynamically unstable characteristics hinder its commercialization. Different approaches have been investigated to enhance its thermochromic property and nanocomposition outperformed other methods by calculation and experiment. The conventional nanocomposite was to disperse VO2 nanoparticles (NP) usually made by the solution process into a transparent media and the highest ΔTsol could only reach 20% theoretically. In this report we employed glass industry compatible process magnetron sputtering followed by rapid thermal annealing (RTA), instead of usual continuous films, such a thin film process gave a unique structure where VO2 NP is dispersed in V2O5/V3O7 matrix with a dense thermodynamic stable V2O5 overcoat. The new type of nanocomposite gives nearly doubled ΔTsol (20%) compared with the best reported continuous vanadium oxides films (10%). Simulation suggested the ΔTsol and Tlum could be further improved to 21.1% and 41.2% by modulating the thickness of V2O5 layer. Simulation suggested that by replacing the conventional transparent matrix, ΔTsol could be further improved from 20.9% to 29.6%. Such combination of ΔTsol (29.6%) and a Tlum (63.8%) outperforms any other theoretical calculation by various surface modifications. The accelerated test suggested that the expected service life of such films is 23 years, which is a breakthrough in VO2 based thermochromic smart window. The high durability due to the encapsulation of V2O5 together with much enhanced thermochromic properties and facile industry compatible process provides a new strategy to scale up this technology into real-world applications.二氧化钒（Vanadium dioxide）作为热致变色智能窗材料被广泛研究，然而其欠佳的热致变色性能（较低的太阳调制能力ΔTsol、可见光透射率Tlum，以及偏高的相变温度τc）与热力学不稳定特性，阻碍了其商业化应用。为改善其热致变色性能，学界已探索多种改性方案，其中纳米复合策略经计算与实验验证，效果优于其他方法。传统纳米复合材料多通过液相法制备二氧化钒纳米颗粒（VO2 nanoparticle, NP），再将其分散于透明介质中，理论上最高太阳调制能力ΔTsol仅可达20%。本研究采用与玻璃工业兼容的磁控溅射（magnetron sputtering）结合快速热退火（rapid thermal annealing, RTA）工艺，未采用传统连续薄膜制备路径，该薄膜工艺获得了独特的微观结构：二氧化钒纳米颗粒分散于五氧化二钒/三氧化七钒（V2O5/V3O7）基体中，表面覆有致密且热力学稳定的五氧化二钒保护层。该新型纳米复合材料的太阳调制能力ΔTsol可达20%，较已报道的最优连续氧化钒薄膜（10%）提升近一倍。模拟研究表明，通过调控五氧化二钒层的厚度，可将太阳调制能力ΔTsol与可见光透射率Tlum进一步优化至21.1%与41.2%；另有模拟结果显示，若替换传统透明基质，则可将太阳调制能力ΔTsol从20.9%提升至29.6%。此时该材料兼具29.6%的太阳调制能力与63.8%的可见光透射率，其综合性能优于此前所有基于表面改性的理论计算结果。加速老化测试表明，该薄膜的预期使用寿命可达23年，这一成果为基于二氧化钒的热致变色智能窗领域带来了突破性进展。得益于五氧化二钒包覆所带来的高耐久性、大幅提升的热致变色性能，以及适配工业化的简便工艺，本研究为该技术规模化落地至实际应用场景提供了全新策略。