Asymmetrical interface design for unidirectional light extraction from spectrum conversion films.

In this study, we propose a micro-sized photonic structure that extracts 89% of the intrinsic trapped photons from the spectrum conversion film into free space using the Monte-Carlo ray-tracing method. Furthermore, the spectrum of the spectral-shifting film can be accurately simulated based on a mean free path concept, providing the estimation of its overall performance including the external quantum efficiency and the self-absorption efficiency. The simulations show that the spectrum conversion film with micro-structures shows a two-fold increase in the total external quantum efficiency and a four-fold increase in the external quantum efficiency in the forward viewing direction compared to the planar spectrum conversion films without micro-structures.

Increasing greenhouse production by spectral-shifting and unidirectional light-extracting photonics.

Improving photosynthesis and light capture increases crop yield and paves a sustainable way to meet the growing global food demand. Here we introduce a spectral-shifting microphotonic thin film as a greenhouse envelope that can be scalably manufactured for augmented photosynthesis. By breaking the intrinsic propagation symmetry of light, the photonic microstructures can extract 89% of the internally generated light and deliver most of that in one direction towards photosynthetic organisms. The microphotonic film augments lettuce production by more than 20% in both indoor facilities with electric lighting and in a greenhouse with natural sunlight, offering the possibility of increasing crop production efficiency in controlled environments.

Scalable-manufactured randomized glass-polymer hybrid metamaterial for daytime radiative cooling.

Passive radiative cooling draws heat from surfaces and radiates it into space as infrared radiation to which the atmosphere is transparent. However, the energy density mismatch between solar irradiance and the low infrared radiation flux from a near-ambient-temperature surface requires materials that strongly emit thermal energy and barely absorb sunlight. We embedded resonant polar dielectric microspheres randomly in a polymeric matrix, resulting in a metamaterial that is fully transparent to the solar spectrum while having an infrared emissivity greater than 0.93 across the atmospheric window. When backed with a silver coating, the metamaterial shows a noontime radiative cooling power of 93 watts per square meter under direct sunshine. More critically, we demonstrated high-throughput, economical roll-to-roll manufacturing of the metamaterial, which is vital for promoting radiative cooling as a viable energy technology.