Smart windows, which are capable of sensing or responding to an external stimulus (e.g. light, heat, or electrical impulse) in a controllable manner, is of particular significance in architecture, transportation, and aerospace industries. For energy-saving, thermochromic materials which exhibit a temperature-induced switch for the transmission/reflection of infrared irradiation have aroused great attention. Without using any external switching device, they can effectively reduce energy consumption triggered by heating, lighting or cooling. A multifunctional coating is crucial for smart windows with ultra-high performance of energy-saving, anti-reflection and self-cleaning. 

Recently, we successfully fabricated novel nanostructured SiO₂/TiO₂/VO₂ TLHNs via a well-controlled interfacial engineering strategy. The TLHNs-based coatings exhibit an excellent balance of optical performance between ultrahigh luminous transmittance (T_lum-l = 74%) and an improved solar modulation ability (ΔT_sol = 12%). Furthermore, the unique design of the partial coverage of TiO₂ nanocrystals in the three-layered structure endows the coating with impressive self-cleaning properties (low contact angle and photocatalytic ability), which is crucial for the practical usage of smart windows. The measured and simulated results reveal that the unique three-layered structure significantly reduces the RI (from 2.25 to 1.33 at 600 nm) and reflectance (Ra from 22.3% to 5.3%) in the visible region, resulting in a prominent optical performance. 

This work demonstrated an exciting inexpensive and universal fabrication process for well-defined structures and may inspire various developments in processable and multi-functional devices. This work entitled “Three-layered hollow nanospheres based coatings with ultrahigh-performance of energy-saving, anti-reflection, and self-cleaning for smart windows” was recently published in small (DOI: 10.1002/smll.201801661). 

This work was supported by the National Key R&D Program of China, the National Natural Science Foundation of China, the Youth Innovation Promotion Association of the Chinese Academy of Sciences and the Presidential Foundation of Technical Institute of Physics and Chemistry.   

 Figure. a) Optical transmittance spectra of VO₂ coating and SiO₂/TiO₂/VO₂ TLHNs coating at low and high temperatures, b/c) energy saving test.