High optical contrast and radiant heat blocking properties of hierarchically structured electrodes for electrochromic windows

Abstract To prepare the electrochromic electrode, a hierarchical structure of ZnO nanorods (2s-ZnR) was grown via the two-step hydrothermal process and used to mitigate electron scattering and improve the optical transmittance of the electrodes. Compared to the electrode with 1s-ZnR, a 36.6% increase in ΔT% (an increase from 24.3 to 33.2) along with fast coloring and bleaching processes (time reduced by 0.4 and 0.6 s, respectively) were achieved with the 2s-ZnR structured electrode. When an optimal sp-WO3 thickness was prepared, the Hier-electrode with a double-hierarchical structure of dip-WO3/sp-WO3/2s-ZnR exhibited a high ΔT% of 50.8, compared to 41.7 and 33.8 analyzed from the Sput- and Dip-electrodes, respectively. When the voltage was switched, the Hier-electrode responded quickly, with tc of 12.7 s and tb of 3.8 s. Moreover, when the heat-irradiation time was extended from 60 to 150 s, the temperature of Hier-electrode only slightly increased by 8.15%. Clearly, the Hier-electrodes exhibit a high contrast ratio, fast response, and high radiant heat blocking capability, which has high potential for smart window applications.