Enhancing the Transparency-Temperature Trade-Off Through Spectral Engineering and Radiative Cooling.

Abstract

Excess solar heat gain limits greenhouse productivity in tropical climates, where conventional polymer covers accumulate thermal energy and allow near-infrared (NIR) transmission. Here, we demonstrate a scalable multilayer greenhouse film that mitigates daytime heat stress through spectral management of solar radiation combined with radiative cooling. A TiO₂-embedded polyethylene terephthalate (PET) scattering layer is laminated with ultraviolet (UV)-IR selective films to prevent excess heat while allowing appropriate photosynthetically active radiation (PAR) transmission. Two configurations are designed to address crop-dependent light requirements: a higher-transmittance film (∼57% PAR) and a stronger heat-rejection film (∼37% PAR). The multilayer structures suppress NIR transmission (up to 80-92% rejection), reduce UV exposure, and exhibit near-unity emissivity within the 8-13 µm atmospheric window (ε¯ ≈ 0.99), enabling efficient radiative heat dissipation. Outdoor rooftop measurements under tropical sunlight demonstrate consistent daytime temperature reductions of 3-5°C compared with those of commercial greenhouse films; the PET-based laminate also provides high mechanical robustness (69-92 MPa tensile strength). These results establish spectral engineering as a practical strategy to manage the transparency-cooling trade-off for passive greenhouse cooling in hot climates.