Phase-change VO₂-based thermochromic smart windows

Thermochromic coatings hold promise in reducing building energy consumption by dynamically regulating the heat gain of windows, which are often regarded as less energy-efficient components, across different seasons. Vanadium dioxide (VO₂) stands out as a versatile thermochromic material for smart windows owing to its reversible metal-to-insulator transition (MIT) alongside correlated structural and optical properties. In this review, we delve into recent advancements in the phase-change VO₂-based thermochromic coatings for smart windows, spanning from the macroscopic crystal level to the microscopic structural level (including elemental doping and micro/nano-engineering), as well as advances in controllable fabrication. It is notable that hybridizing functional elements/materials (e.g., W, Mo/SiO₂, TiN) with VO₂ in delicate structural designs (e.g., core-shell, optical cavity) brings new degrees of freedom for controlling the thermochromic properties, including the MIT temperature, luminous transmittance, solar-energy modulation ability and building-relevant multi-functionality. Additionally, we provide an overview of alternative chromogenic materials that could potentially complement or surpass the intrinsic limitations of VO₂. By examining the landscape of emerging materials, we aim to broaden the scope of possibilities for smart window technologies. We also offer insights into the current challenges and prospects of VO₂-based thermochromic smart windows, presenting a roadmap for advancing this field towards enhanced energy efficiency and sustainable building design. In summary, this review innovatively categorizes doping strategies and corresponding effects of VO₂, underscores their crucial NIR-energy modulation ability for smart windows, pioneers a theoretical analysis of inverse core-shell structures, prioritizes practical engineering strategies for solar modulation in VO₂ films, and summarizes complementary chromogenic materials, thus ultimately advancing VO₂-based smart window technologies with a fresh perspective.