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Radiative cooling technology can emit infrared heat to the outer space through the "sky window" for cooling without consuming energy, which had drawn more and more attention. However, some researches reported that there was a significantly different cooling performance at different atmospheric total water vapor columns (TWC) conditions. In this study, taking a simple single-layer radiative cooling coating containing two kinds of particle mixture (SiO2, TiO2) as example, the spectral effective emissivity of the radiative cooling coating was proposed to evaluate the effect of the atmospheric water vapor on the cooling performance. The spectral effective emissivity of the coating was obtained through multiplying spectral emissivity of the coating by the atmospheric transmittivity, where the spectral emissivity was calculated by combining an algorithm for calculating radiative properties of the multi-particle system with the Monte Carlo ray-tracing method (MCRT). The effects of different atmospheric water vapor on the spectral effective emissivity of the simple single-layer radiative cooling coating containing different particles size, volume fraction and thickness were studied to improve the cooling performance of the coating. The results showed that with increasing TWC from 0 to 7000 atm-cm, the average effective emissivity of the simple single-layer coating decreased from 79.5% to 35.3%, with a decrease of 44.2%. The research results are of great significance to the further application development and the design criterion of radiative cooling materials in different atmospheric water vapor environments.

Common glass without spectral regulation effect cannot offer an energy‐saving function, and radiative cooling technology without visible transparency cannot satisfy the illumination and esthetic demands. Herein, the concept of utilizing a biomimetic beetle cuticle structure, guided by principles of Chinese Taoist philosophy, is proposed to accomplish efficient radiative regulation. Subsequently, low‐cost biomimetic radiative cooling (Bio‐RC) glass is presented, which can reduce the temperature of buildings throughout daytime by blocking near‐infrared (NIR) radiation, conveying visible light, and emitting heat within the atmospheric window. Utilizing only three layers of thin films, Bio‐RC glass achieves multi‐band spectral regulation, avoids a complicated preparation process, and has the potential for large‐scale production. Spectrometry reveals that Bio‐RC glass exhibits an effective visible light transmissivity of 80.5%, a mean NIR transmissivity of 10.3%, and an effective emissivity of 94.8% within the atmospheric window. A one‐month rooftop test demonstrates that Bio‐RC glass achieves a maximum cavity temperature reduction of 18.1 °C compared with common glass. Energy consumption analysis indicates that Bio‐RC glass can conserve approximately 23.4% of the total energy consumption per year compared with common glass. The proposed Bio‐RC glass can lower the temperature during daylight while preserving transparency and esthetics, making it suitable for application in buildings and vehicles. [ABSTRACT FROM AUTHOR]

Hydrogen production from water using a catalyst and solar energy was an ideal future fue l source. In this study, an elaborate experimental test rig of hydrogen production from solar water splitting was designed and established with self-controlled temperature system. The effects of light intensity on the reaction rate of hydrogen production from solar water splitting were experimentally investigated with the consideration of optical losses, reaction temperature, and photo-catalysts powder cluster. Besides, a revised expression of full-spectrum solar-to-hydrogen energy conversion efficiency with the consideration of optical losses was also put forward, which can be more accurate to evaluate the full-spectrum solar-to-hydrogen energy of photo-catalysts powders. The results indicated that optical losses of solar water splitting reactor increased with the increase of the incoming light intensity, and the hydrogen production rate increased linearly with the increase of effective light intensity even at higher light intensity region when the optical losses of solar water splitting reactor were considered. [ABSTRACT FROM AUTHOR]

The perovskite solar cell (PSC) has the benefits of flexibility, inexpensiveness, and high efficiency, and has important prospective applications. However, serious optical losing and low solar energy-utilizing efficiency remain a challenge for the ultra-thin PSCs because of the interface reflection of traditional planar structure. In this study, a hierarchical pore structure with a confined resonant mode is introduced and optimized by electromagnetic theory to improve the solar energy absorbing and utilizing efficiency of ultra-thin PSCs. The large pores in the top layer that support a whispering gallery mode can focus and guide the incident light into the solar cell. The small pores in the bottom layer enable backward scattering of the unabsorbed light and can improve the effective absorption of active layer. The finite-difference time-domain method is employed to optimize the geometric parameters of hierarchical pore structure to improve the light absorption of PSCs. The proposed resonant hierarchical pore structure can greatly improve sunlight absorption of ultra-thin PSCs, and the effective light absorption and photocurrent of PSCs with a hierarchical pore structure is 20.7% higher than that of PSCs with traditional planar structure. This work can offer a beneficial guideline for improving solar energy utilizing efficiency of various thin-film solar cells.

Radiative cooling is a passive cooling method that does not consume additional energy and has broad application prospects. In recent studies, the surface microstructure was found to have a significant influence on improving the emissivity in infrared spectra for radiative cooling. Accordingly, in this paper, an innovative wrinkled surface microstructure without any periodicity is proposed for enhancing the infrared spectral performance of radiative cooling. The effects of the height and number of wrinkles as well as the radius and volume fraction of particles on the infrared spectral performance of radiative cooling are investigated. The radiative cooling performances of the plane, pyramid, moth-eye, and wrinkled microstructures are comparatively investigated using the finite-difference time-domain (FDTD) method. The results show that the mean emissivity of innovative radiative cooling films with the wrinkled surface microstructure reaches 99.58% in the "atmospheric window" wavelength range. The mean emissivity of the wrinkled microstructure is improved by 19%, 22.16%, and 8.41% over those of the plane, pyramid, and moth-eye microstructures, respectively. This indicates that the wrinkled microstructure exhibits a better performance for radiative cooling than single periodic surface microstructures. Furthermore, the wrinkled microstructure has no periodicity so it has low production cost, which makes it possible to replace other periodic surface microstructures.