Smart windows with self-adaptive emittance modulation based on patterned grating

• Designed a smart window composed of an HMM and patterned grating. • Capable of large emittance modulation with Δ ε LWIR of 0.830. • maintaining high and low transmittance in the VIS and NIR bands. • Underlying mechanisms involve FP and MP resonance. • Quantitatively demonstrated the energy conservation for terrestrial application. Smart windows represent a pivotal technology for building energy conservation, aiming to provide high visible transmittance for adequate daylighting, low near-infrared transmittance to minimize solar heat gain, and adaptive long-wave infrared (LWIR) emittance modulation for efficient radiative cooling or thermal retention. However, achieving all these properties simultaneously is challenging. In this work, we designed a smart window with a VO 2 /BaF 2 grating pattern fabricated on a multilayer Ag/SiO 2 substrate by combining the Genetic Algorithm with the Rigorous Coupled Wave Analysis method. Leveraging the phase transition of VO 2 , our design achieves an exceptional emittance tunability of 0.830 in the LWIR atmospheric window. Crucially, this high emittance modulation is accomplished while maintaining excellent visible transmittance of 0.700 and low near-infrared transmittance of 0.265, effectively decoupling the regulation of solar and thermal radiation. The underlying mechanism involves the manipulation of Fabry-Pérot and Magnetic Polaritons resonance. Furthermore, the window shows excellent angular stability and, at the phase transition, enables tunable emitting power exceeding 300 W/m 2 . This work supports the evolution and deployment of smart windows for building energy efficiency.