A Multifunctional Smart Window for Adaptive Solar, Thermal, and Electromagnetic Management in Buildings

ABSTRACT Smart windows could reduce building energy demand, but most regulate only one or two spectral bands and do not address the increasingly complex electromagnetic environments of modern buildings. Here we report a multifunctional window that combines electrochemical switching with low‐frequency mechanical reorientation to control visible, near‐infrared, long‐wave infrared, and microwave responses. A transparent Ti 3 C 2 T x MXene electrode ( T 550 nm > 60%, R s ≈ 40 Ω/sq) and a PEDOT:PSS layer enable electrochemical regulation of glare and solar heat gain through coupled visible–near‐infrared optical switching. Reorientation of a Janus interface switches the outward long‐wave emissivity ( ε LWIR ) between ∼0.83 and ∼0.38 for cooling‐ and heating‐oriented operation. The device also shows reversible X‐band shielding modulation from 15.5 to 20.2 dB. Comparative chamber tests, climate‐resolved building simulations and carbon accounting suggest reduced annual HVAC demand and associated CO 2 emissions in representative climates.