Antireflective-to-mirror-like all-solid-state electrochromic devices

Abstract

Inorganic electrochromic (EC) materials, capable of transitioning between bleached and colored states under an applied current, hold significant potential for smart windows and eyewear industries. These materials can be integrated into all-solid-state devices (ASSDs) consisting of two electrodes, with tungsten trioxide (WO₃) and nickel oxide (NiO) as complementary EC layers, separated by an ion conductor. While standard architectures enable significant transmission and absorption modulation, their ability to achieve a substantial reflection increase upon coloration remains limited, which can be of interest for enhanced aesthetics and improved user comfort. To address this limitation, an EC Bragg mirror composed of alternating layers of WO₃ and indium tin oxide (ITO) was implemented to replace the single WO₃ layer in the standard architecture. This improved design enabled enhanced ASSD reflection modulation, effectively transitioning from an antireflective to a mirror-like state by reaching a 7.6 % increase in reflection. Simplifying the ASSD structure by omitting the antireflective constraints, the devices were able to reach an even greater reflection modulation of up to 17.9 %. A modeling approach based on transfer matrix calculations was employed to predict the optical behavior of the fabricated ASSDs in both their bleached and colored states. Despite some discrepancies in the spectral fitting, the presence of a distinct peak confirmed the effectiveness of Bragg mirror-integrated EC devices. Finally, durability testing revealed that the cycling stability of the enhanced devices strongly depends on the applied electrode potentials, highlighting their critical role in maintaining performance over time.