Innovative dual-band energy-efficient smart windows using VO2(M)-Based Fabry-Pérot structures for solar and radiative cooling modulation

Abstract

Thermochromic windows have been studied as a promising solution for energy-efficiency with the dynamical adjustment of solar heating in response to temperature. Recent advancements in the field have introduced simultaneous multiband modulation, incorporating radiative cooling in the longwave infrared range. In this work, we present VO₂(M)/TiO₂(A)/ITO multilayer-coated glass (referred to as VTI) as a scalable and effective smart window that modulates both solar transmission and radiative cooling concurrently. As a semitransparent window in the solar spectrum, the VTI coating achieves nearly 100 % visual clarity, 38.5 % visible transparency, and 8.5 % modulation of solar transmittance. In the longwave infrared region, the VTI multilayer demonstrates an exceptional broadband emissivity shift of up to 42.5 %, made possible by an innovative Fabry-Pérot (F-P) cavity composed of absorbing metal oxides. This high degree of emissivity modulation is maintained across a wide range of spacer thicknesses, from 100 to 500 nm, as confirmed by both experimental data and simulations. The modulation mechanism of the F-P cavity which use ultrathin spacer (λ/140 ∼ λ/16) at its resonant absorption range is explained through incremental phasor analysis by the transfer-matrix method. Additionally, the scalability and practicality of the VTI film are supported by its three-layer composition and the room-temperature reactive magnetron sputtering deposition process. These results suggest that the design principles presented here could inspire further innovations in broadband longwave infrared emissivity modulation, utilizing ultrathin F-P cavities composed of semitransparent metal oxides.