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

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