Hetero-order coupled cavity electrochromic mirrors enabling high-purity, wide-gamut, and broad-angle multicolor displays

Abstract

Multicolor electrochromic (EC) materials and devices enable reversible optical modulation under low driving voltages, holding considerable potential for application in next-generation low-power displays. However, the development of inorganic EC materials is fundamentally constrained by their narrow intrinsic color gamut. Structural-color-based strategies have been explored to achieve multicolor tuning, yet simultaneously achieving high color purity, high saturation, and a wide viewing angle remains a significant challenge. Herein, we propose a novel hetero-order coupled cavity electrochromic mirror (HCCECM) that exploits resonant coupling and mode selection between adjacent second-order and first-order Fabry–Perot cavities. The distinctive architecture generates a sharp, intense primary reflection peak while effectively suppressing higher-order modes and minimizing angular-dependent spectral shifts. The resulting EC films exhibit superior optical performance, including high reflectance (>90%), narrow bandwidth (FWHM <70 nm), a high quality factor of 9.0, and excellent angular color stability (spectral shift <20 nm over ±60° incidence). Moreover, the HCCECM attains a color gamut that exceeds the sRGB standard. During the EC process, the HCCECM demonstrates remarkable multicolor modulation with a high optical contrast (>70%), fast response speeds (4.5 s for coloration and 1.9 s for bleaching), and good cycling stability (85.6% of the initial optical contrast after 5000 cycles). A proof-of-concept RGB-patterned EC display is further constructed, successfully achieving reversible modulation from vivid colors to black. This work provides an effective design strategy for developing next-generation high-performance EC materials and devices.