Colored and paintable bilayer coatings with high solar-infrared reflectance for efficient cooling

TLDR

Solar‑reflective, thermally emissive surfaces provide sustainable cooling, yet their typical white or silvery appearance fails to meet color requirements. This work introduces a paintable bilayer coating that simultaneously delivers color and radiative cooling. The bilayer consists of a thin, visible‑absorbing top layer that imparts color and a non‑absorbing, solar‑scattering underlayer that maximizes near‑to‑short‑wave infrared reflection. The bilayer achieves 0.1–0.51 higher NSWIR reflectance and reduces temperatures by 3.0–15.6 °C compared to commercial paint monolayers, with a blue variant reaching 0.89 reflectance, demonstrating a simple, inexpensive, scalable solution.

Abstract

Solar reflective and thermally emissive surfaces offer a sustainable way to cool objects under sunlight. However, white or silvery reflectance of these surfaces does not satisfy the need for color. Here, we present a paintable bilayer coating that simultaneously achieves color and radiative cooling. The bilayer comprises a thin, visible-absorptive layer atop a nonabsorptive, solar-scattering underlayer. The top layer absorbs appropriate visible wavelengths to show specific colors, while the underlayer maximizes the reflection of near-to-short wavelength infrared (NSWIR) light to reduce solar heating. Consequently, the bilayer attains higher NSWIR reflectance (by 0.1 to 0.51) compared with commercial paint monolayers of the same color and stays cooler by as much as 3.0° to 15.6°C under strong sunlight. High NSWIR reflectance of 0.89 is realized in the blue bilayer. The performances show that the bilayer paint design can achieve both color and efficient radiative cooling in a simple, inexpensive, and scalable manner.