Index-matched hollow silica colloidal crystals for structurally colored radiative cooling on white reflectors

초록

Although reflection-based structurally colored radiative coolers offer low solar absorption, their high optical transmittance necessitates white reflectors, whose broadband back-reflection causes severe chromatic wash-out. Here, we report refractive-index-matched hollow SiO2 colloidal crystals (CCs) that suppress this wash-out at the material level, enabling pastel-colored radiative coolers on white polytetrafluoroethylene reflectors. Comparative analysis of conventional solid and inverse SiO2 CCs reveals that Bragg-reflective hollow SiO2 CCs scatter transmitted light before it reaches the reflector, generating a spectrally correlated internal scattering background that preserves structural color, unlike substrate back-reflection that washes out hue. Importantly, polydimethylsiloxane infiltration is essential to moderate the excessive scattering of bare hollow SiO2 CCs through refractive-index matching, thereby restoring the Bragg-reflective response. Two photonic coolers with different particle diameters and shell thicknesses exhibit pastel green and orange tones while maintaining high infrared emissivity. Compared with color-matched commercial paints, they achieve midday temperature reductions of ∼8 °C and cooling-power improvements of 112.2 and 156.2 W m–2, respectively. Building-energy simulations further confirm that applying these photonic coolers reduces building cooling energy consumption compared to same-colored commercial paint baselines. We highlight our approach as a unique tool for combining structural coloration with radiative cooling on white reflectors, effectively mitigating solar absorption and reducing thermal load. © 2026 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

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