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/m² under solar intensity of ~900 W/m², and promisingly ~5.5 °C even under solar intensity of ~930 W/m² 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.

近来，全天被动辐射冷却通过反射阳光并将热量辐射到超冷的外层空间而引起了极大的兴趣。尽管已经取得了一些进展，但在为全天候和全气候制造高效，低成本的辐射冷却器方面仍然是巨大的挑战。本文中，我们报告了一种具有微孔阵列和随机纳米孔相结合的分层结构的聚甲基丙烯酸甲酯（PMMA）膜，用于高效的日夜被动辐射冷却。这种多层多孔的PMMA膜具有足够高的日光反射率（0.95）和卓越的长波红外热发射率（0.98），可在夜间实现约8.2°C的低温冷却，在中午实现约6.0°C到〜8.9°C的平均冷却。制冷功率〜85 W / m ²在〜900 W / m ^2的太阳强度下，甚至在〜930 W / m ^2的太阳强度和〜64 ％的相对湿度下，在炎热和潮湿的气候下，有望达到〜5.5°C 。聚合物膜中的微孔和纳米孔在增强太阳光反射率和热辐射率方面起着至关重要的作用。