Wide-Gamut and High-Saturation Electrochromic Displays Enabled by Optical-Thickness Engineered Nanocavities

Electrochromic (EC) displays offer low-power consumption and bistable operation but are intrinsically constrained by a limited color gamut and insufficient color saturation. Herein, we report an optical-thickness engineered Al/WO₃/W/WO₃ metal-dielectric-metal-dielectric (MDMD) architecture for wide-gamut, highly saturated color EC displays. By tailoring the optical thickness of the outer WO₃ layer to λ/4, λ/2, or λ, wavelength-selective interference is achieved, enabling suppression of parasitic reflection peaks and narrowing of the reflection bandwidth beyond conventional Fabry-Pérot cavities. The optimized MDMD structure achieves ∼90% coverage of the standard RGB color space with near-unity color saturation. Notably, the MDMD electrode with a 93 nm WO₃ layer exhibits reversible switching from cyan to deep blue while maintaining full color saturation, enabled by potential-controlled Li⁺ insertion/extraction that dynamically modulates the optical constants and shifts the nanocavity resonance. This work establishes optical-thickness engineering as an effective strategy for simultaneously enhancing color gamut and saturation in EC displays.