The application of asymmetric transmission in daytime radiative cooling cannot increase the cooling power

Highlights

• We argue here that the cooling power cannot be improved by integrating the radiative cooler with an AT device.

• It is proved that AT can be realized in reciprocal materials only when there is mode-to-mode conversion.

• The ray tracing method is not appliable to AT device because it does not take mode-to-mode conversion into account.

Abstract

Recently, the asymmetric transmission has been employed to enhance the cooling power of daytime radiative cooler [Wong et al., Solar Energy Materials and Solar Cells 2018, 186: 330–339]. we argue here that the radiative cooling power cannot be improved by integrating the radiative cooler with an asymmetric electromagnetic transmission device. The reason is that the equivalence between the absorption and emission of the whole structure cannot be broken by adding the asymmetric transmission device. The theoretical analyses are provided to tackle this problem. The scattering matrix method is used to prove that the asymmetric transmission can be realized in reciprocal materials only when there is mode-to-mode conversion. However, the ray tracing method did not take the mode-to-mode conversion into account in Wong's paper, thus the absorption and emission of the whole structure could not be accurately calculated. We believe this work can prevent researchers from advancing in the improper way.