title: Radiative cooling to deep sub-freezing temperatures through a 24-h day-night cycle.
abstract: Radiative cooling technology utilizes the atmospheric transparency window (8-13 μm) to passively dissipate heat from Earth into outer space (3 K). This technology has attracted broad interests from both fundamental sciences and real world applications, ranging from passive building cooling, renewable energy harvesting and passive refrigeration in arid regions. However, the temperature reduction experimentally demonstrated, thus far, has been relatively modest. Here we theoretically show that ultra-large temperature reduction for as much as 60 °C from ambient is achievable by using a selective thermal emitter and by eliminating parasitic thermal load, and experimentally demonstrate a temperature reduction that far exceeds previous works. In a populous area at sea level, we have achieved an average temperature reduction of 37 °C from the ambient air temperature through a 24-h day-night cycle, with a maximal reduction of 42 °C that occurs when the experimental set-up enclosing the emitter is exposed to peak solar irradiance.
authors.affiliation: Ginzton Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California 94305, USA.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Department of Applied Physics, Stanford University, Stanford, California 94305, USA.
authors.forename: Linxiao
authors.identifier: 0000-0001-9465-597X
authors.initials: L
authors.lastname: Zhu
authors.affiliation: Ginzton Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California 94305, USA.
authors.forename: Aaswath
authors.identifier: 0000-0003-0106-8341
authors.initials: A
authors.lastname: Raman
authors.affiliation: Ginzton Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California 94305, USA.
authors.forename: Shanhui
authors.initials: S
authors.lastname: Fan