A structural polymer for highly efficient all-day passive radiative cooling

TLDR

All‑day passive radiative cooling has attracted interest by reflecting sunlight and radiating heat to outer space, yet fabricating highly efficient, low‑cost coolers for all‑day and all‑climates remains a big challenge. Here we report a hierarchically structured PMMA film with a micropore array combined with random nanopores designed for highly efficient day‑ and nighttime passive radiative cooling. The film’s hierarchical micropore array and random nanopores enhance solar reflectance and thermal emittance, enabling efficient day‑ and nighttime passive radiative cooling. The hierarchically porous PMMA film achieves 0.95 solar reflectance, 0.98 infrared emittance, and subambient cooling of ~8.2 °C at night and 6.0–8.9 °C during midday, with an average cooling power of ~85 W m⁻² under ~900 W m⁻² solar intensity, and ~5.5 °C even under ~930 W m⁻² and 64 % humidity in hot, moist climates.

Abstract

Abstract All-day passive radiative cooling has recently attracted tremendous interest by reflecting sunlight and radiating heat to the ultracold outer space. While some progress has been made, it still remains big challenge in fabricating highly efficient and low-cost radiative coolers for all-day and all-climates. Herein, we report a hierarchically structured polymethyl methacrylate (PMMA) film with a micropore array combined with random nanopores for highly efficient day- and nighttime passive radiative cooling. This hierarchically porous array PMMA film exhibits sufficiently high solar reflectance (0.95) and superior longwave infrared thermal emittance (0.98) and realizes subambient cooling of ~8.2 °C during the night and ~6.0 °C to ~8.9 °C during midday with an average cooling power of ~85 W/m 2 under solar intensity of ~900 W/m 2 , and promisingly ~5.5 °C even under solar intensity of ~930 W/m 2 and relative humidity of ~64% in hot and moist climate. The micropores and nanopores in the polymer film play crucial roles in enhancing the solar reflectance and thermal emittance.