Radiative cooling film enabled by droplet-like infrared hot spots via low-cost and scalable spray-coating process for tropical regions

Radiative cooling is a passive cooling process to reduce temperature by emitting infrared radiation in the atmospheric window range of 8–13 μm. In this work, droplets and wrinkles, which can induce Mie scattering and therefore increase emissivity, are generated via low-cost and scalable spray coating to enable economical radiative cooling production (∼$0.05/m2). Tested during the daytime with ∼920 W m−2 and ∼58% relative humidity in Thailand, the double layer consisting of droplets on top of a polydimethylsiloxane flat film can lead to a temperature reduction of 1.22°C and 3.61°C below the baseline temperature (without the coating) under an airflow test box and a closed test box, respectively. Furthermore, cooling stability and applicability on functional substrates such as glass, wood, and roof tiles are investigated. To demonstrate scalability, a commercial spray gun is used as an all-in-one technique for fabrication, achieving a similar temperature reduction and opening doors for commercialization.