Isotope-driven hydrogel smart windows for self-adaptive thermoregulation

As a cutting-edge and environmentally friendly approach, thermochromic hydrogel smart windows show great potential in combating climate change and achieving carbon neutrality. However, the substantial absorption of near-infrared (NIR) energy by H₂O poses an enormous challenge in enhancing the spectral responsiveness. Herein, we propose an ingenious concept of isotope-driven D₂O-hydrogel smart windows, which can effectively resolve the inherent issue of NIR energy absorption associated with H₂O, without compromising versatility. It facilitates near-optimal transmittance modulation across the entire solar spectrum (ΔΓ_Sol = 91.97%), demonstrating a marked enhancement in NIR modulation of transmittance (ΔΓ_NIR) and reflectance (ΔR_NIR) by ~16% and ~31%, respectively, in comparison to conventional H₂O-hydrogel. Moreover, the integration of Ag-nanowires into D₂O-hydrogel further substantially augments the regulation of longwave infrared emissivity ( $\Delta {\epsilon }_{LWIR}$  = 31.89%) while preserving a comprehensive modulation ratio (ΔΓ_Sol = 66.02%, ΔR_Sol = 48.41%) that is not achieved by the existing thermochromic devices. This isotope-driven D₂O-hydrogel smart window provides another design strategy for future energy-efficient windows.