First-principles theory-based design of highly reflective metals for radiative cooling

Motivated by recent great progress in passive radiative cooling, we performed a first-principles-based material design study of high reflectivity mirror components. From the electronic structure analysis on noble metals, we found that the control of the d-to-sp band transition can be the key to achieve the better reflection performance than pure silver. As concrete examples, we first suggest electron doping into Ag through, e.g., Cd alloying. Our simulation results show that, by 10% Cd alloying, Ag0.9Cd0.1 exhibits the reflectivity drop starting at the higher photon energy than silver. The second is to use alkali metal whose stable treatment has recently been much more feasible. Two alkali metals, namely sodium and lithium, also show the higher energy reflectivity drop which is attributed to the absence of localized d-electron bands below the Fermi energy. Our study provides the useful insight for designing better mirror materials and hopefully stimulates further theoretical and experimental investigations.