Durability enhancement of all-solid-state electrochromic devices by adjusting the charge density ratio between electrochromic and counter electrode layers

초록

Owing to an increase in global warming smart-window devices based on charge-balanced electrochromic devices (ECDs) which exhibit high potential to increase the thermal efficiency of buildings have gained prominence. However studies on the fabrication and cycling stability of charge-balanced ECDs are scarce. In this study WO3 and NiOx films were deposited on indium–tin–oxide (ITO)-coated glass substrates by reactive direct-current magnetron sputtering and the deposition time was varied to control the thickness and charge density of the thin films. Subsequently the NiOx/ITO/glass and WO3/ITO/glass substrates were laminated with a Li-based polymeric electrolyte to fabricate all-solid-state ECDs comprising electrochromic (EC) and counter-electrode (CE) layers in charge-density ratios of 12.6 6.4 2.3 and 1.1. Changes in the electrochromic properties device-layer microstructure crystal structure and elemental composition of the as-constructed ECDs before and after degradation were investigated to understand the influence of the charge-density ratio of the EC and CE layers on the long-term durability of ECDs. Increasing the charge-density ratio decreased the cycling stability of the device owing to changes in the microstructure and crystal structure of the NiOx layer in the microstructural deep-trap sites. Among all the ECDs those comprising EC and CE layers with similar charge densities showed the most stable optical modulation and highest long-term durability. Finally based on the aforementioned results a degradation mechanism for charge-imbalanced all-solid-state ECDs was proposed. This study is expected to open new frontiers in designing optimal-performance electrochemical devices with a wide variety of potential applications. © 2024

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