Figure 3. Radiative cooling devices. (a) Comparison study of a radiative cooling roof and a regular shingle roof. Reprinted with permission from ref 13. Copyright 2019 Elsevier. (b) Wood-based building material for radiative cooling. Reprinted with permission from ref 18.

Interfacial solar steam/vapor technology uses abundant and clean solar energy and water to achieve heating and cooling, a promising technology to alleviate environmental and energy issues. To obtain higher conversion and utilization efficiency, designing and optimizing materials, structures, and devices of interfacial solar steam/vapor technologies attract the attention of the research community. Given the significant progress made in the past 5 years, it is valuable to systematically summarize and discuss recent developments and future trends in this new multidisciplinary direction. This review aims to introduce interfacial solar steam/vapor principles to realize heating and cooling and the recent progress in materials, structures, devices, and applications. Meanwhile, some unsolved scientific and technical problems with outlook will also be discussed, hoping to promote further the rapid development and application of interfacial solar steam/vapor technology in heating and cooling to alleviate energy and environmental problems.

Thermal management is ubiquitous in the modern world and indispensable for a sustainable future. Radiative heat management provides unique advantages because the heat transfer can be controlled by the surface. However, different object emissivities require different tuning strategies, which poses challenges to develop dynamic and universal radiative heat management devices. Here, we demonstrate a triple-mode midinfrared modulator that can switch between passive heating and cooling suitable for all types of object surface emissivities. The device comprises a surface-textured infrared-semiabsorbing elastomer coated with a metallic back reflector, which is biaxially strained to sequentially achieve three fundamental modes: emission, reflection, and transmission. By analyzing and optimizing the coupling between optical and mechanical properties, we achieve a performance as follows: emittance contrast Δε = 0.58, transmittance contrast Δτ = 0.49, and reflectance contrast Δρ = 0.39. The device can provide a new design paradigm of radiation heat regulation for wearable, robotics, and camouflage technologies.

Clean drinking water is increasingly perceived as one of the most critical global challenges. Direct solar desalination with a minimal carbon footprint is a promising technology to alleviate the water challenge. However, this technology still faces a series of problems, such as poor salt-rejection of the absorber and low condensation efficiency and water output. Currently, the design and utilization of infrared light shows unique advantages in solving these problems. With this background, this Focus Review aims to summarize the state-of-the-art progress of three infrared-light-based strategies for direct solar desalination: the use of selective absorbers to obtain higher solar-to-vapor conversion efficiency, the use of radiative energy to indirectly heat the water to resolve the salt-rejecting problem of the absorber, and use of radiative cooling to enhance the output of freshwater. Also, unsolved scientific and technical issues associated with the outlook in these directions are discussed, with the hope of further promoting direct solar desalination for sustainability and global welfare.