Technologies enabling passive daytime radiative cooling and daylight harvesting are highly relevant for energy-efficient buildings. Despite recent progress demonstrated with passively cooling polymer coatings, however, it remains challenging to combine also a passive heat gain mechanism into a single substrate for all-round thermal management. Herein, we developed an optical wood (OW) with switchable transmittance of solar irradiation enabled by the hierarchically porous structure, ultralow absorption in solar spectrum and high infrared absorption of cellulose nanofibers. After delignification, the OW shows a high solar reflectance (94.9%) in the visible and high broadband emissivity (0.93) in the infrared region (2.5–25 μm). Owing to the exceptional mass transport of its aligned cellulose nanofibers, OW can quickly switch to a new highly transparent state following phenylethanol impregnation. The solar transmittance of optical wood (OW-II state) can reach 68.4% from 250 to 2500 nm. The switchable OW exhibits efficient radiative cooling to 4.5 °C below ambient temperature in summer (cooling power 81.4 W m), and daylight heating to 5.6 °C above the temperature of natural wood in winter (heating power 229.5 W m), suggesting its promising role as a low-cost and sustainable solution to all-season thermal management applications.

中文翻译：

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具有可切换太阳能透射率的光学木，可实现全方位热管理

实现被动日间辐射冷却和日光收集的技术与节能建筑高度相关。尽管最近在被动冷却聚合物涂层方面取得了进展，但将被动吸热机制结合到单个基板中以进行全方位热管理仍然具有挑战性。在此，我们开发了一种光学木（OW），其通过纤维素纳米纤维的分级多孔结构、太阳光谱的超低吸收和高红外吸收来实现太阳辐射透射率的切换。脱木素后，OW 在可见光区域表现出高太阳反射率 (94.9%)，在红外区域 (2.5–25 μm) 表现出高宽带发射率 (0.93)。由于其排列的纤维素纳米纤维具有出色的传质能力，OW 可以在苯乙醇浸渍后快速切换到新的高度透明状态。光学木（OW-II态）的太阳光透过率在250~2500 nm范围内可达68.4%。可切换的 OW 表现出高效的辐射冷却，夏季比环境温度低 4.5 °C（冷却功率 81.4 W m），冬季日光加热比天然木材温度高 5.6 °C（加热功率 229.5 W m），这表明其前景广阔作为全季节热管理应用的低成本且可持续的解决方案。