All-in-one electrochromic device based on an inorganic-organic dual redox synergistic system for smart windows

All-in-one electrochromic devices (ECDs) integrate all active components into a single electrolyte layer, yet their performance remains constrained by the inherent trade-off between optical contrast and switching kinetics in single-component systems. Here we report a conceptually new design strategy based on inorganic-organic dual redox pairs, wherein the electrochromic function and the charge-balancing function are assigned to two distinct yet electrochemically coupled components within a poly(ethylene oxide) (PEO) composite electrolyte. More importantly, the resulting colorless electrolyte incorporates a dual redox couple: the organic pair of transparent tetramethyl-thiourea (TMTU) and its oxidized dimer tetramethylformaminium disulfide dication (TMFDS²⁺), mediates charge compensation and accelerates switching kinetics without introducing parasitic absorption, while the inorganic oxidized state of silicotungstic acid (STA) serves as the electrochromic component, providing multi-electron W⁶⁺/W⁵⁺ redox capacity with intense blue coloration for electrochromic smart windows (ESWs). The advantages of this organic-inorganic hybrid dual redox couple include its non-corrosive nature, low cost, and easy handling. The all-in-one device adopts a simplified indium tin oxide (ITO)/composite electrolyte/ITO architecture, eliminating the electrochromic and ion-storage layers of conventional designs. The optimized device achieves an optical contrast of 93.8 ± 0.6% (without ITO), a coloration time of 3.2 ± 0.2 s, a coloration efficiency (CE) of 339.5 cm² C^-1, and 10,000-cycle stability with negligible degradation. Large-area prototypes (100 cm²) exhibit uniform coloration. This dual redox strategy establishes a modular platform for high-performance all-in-one ECDs with independently tunable components.