Collaborative Research: Designing Thermophotonic Materials for Passive Radiative Cooling

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Passive radiative cooling allows for cooling below ambient conditions without the input of external energy. It involves a radiative thermal body directly exchanging electromagnetic thermal energy with outer space, an enormous and extremely cold heat sink. Passive radiative cooling can make refrigeration and climate control run more efficiently, saving significant amounts of energy. However, traditional radiative cooling does not work during the daytime because of the absorption of sunlight. The difficulty in realizing effective passive radiative cooling lies in controlling the energy exchange for the competing mechanisms of thermal radiation, optical absorption and heat transfer in the cooling system. This award supports fundamental research to provide the knowledge for the design and processing of thermophotonic materials that can meet the stringent optical and thermal requirements. These new thermophotonic materials will be realized through optimally designed, microscopically structured materials that can be tailored through micro- and nano-fabrication to produce the desired optical and thermal responses. With such material, the cold darkness of outer space can be leveraged as a renewable thermodynamic resource for providing passive cooling here on Earth. This research will involve predictive modeling of optical reflection and absorption and heat transfer behaviors of sub-micro- and nano-structured materials in order to understand the nature of thermophotonic coupling and the nonlinearity of material properties. A topology optimization-based method will be created to systematically explore the design space and to identify the viability of multiple nano-structured materials. This method will account for thermophotonic coupling, spectral selectivity, and manufacturability constraints. It will lead to the discovery of new micro- and nano-structured material systems that have effective material properties meeting the stringent thermal and optical requirements for passive radiative cooling during daytime. The resulting designs will be validated with experimental prototyping. If successful, this research will result in disruptive thermophotonic material systems that can lead to cooling below ambient temperature during the day without the need for external energy input.