Novel thermotropic system with UV-blocking ability for dynamic radiative cooling and synchronous visible/NIR tuning of windows in buildings in hot climate regions

Passive dynamic thermotropic (TT) radiative cooling (RC) windows aid net-zero energy buildings in smart cities by adjusting sunlight and solar heat in response to temperature variations, as they become opaque when temperatures rise, thereby using thermal radiation to dissipate heat into outer space. They are ideal for controlling solar heat gain and privacy. Here we introduce an innovative eco-friendly TT layer with UV-shielding and RC ability composed of a sol-gel derived di-ureasil hybrid matrix doped with carbon dots (CDs) obtained from Agapanthus africanus leaves and variable contents of TT 1-butyl-3-methylimidazolium chloride ([BMIm]Cl) ionic liquid. The layers exhibit high transparency and thermal stability. The thermotropic devices (TTDs) assembled demonstrated, at the highest [BMIm]Cl concentration used, improved thermo-optical performance mediated by the surface plasmon resonance effect (SPRE), broad operational range (30–70°C), and excellent cycling stability. Maximum transmittance variation (ΔT) values of 31/27% at 550/1100 nm were achieved. This new class of TT layer represents a milestone in the development of smart RC materials for autonomous solar modulation windows.