Gradient oxygen vacancy–mediated ion-coupled charge transfer for ultra-stable all-solid-state electrochromic smart windows

The practical deployment of all-solid-state electrochromic smart windows (ESWs) is hinderedby a high “desolvation-like” energy barrier and chemo-mechanical degradation at the buried electrode/solid-electrolyte heterointerface, where passively formed physical contacts inevitably fail under cumulative cyclic stress. Here, we overcome this challenge by constructing a gradient oxygen vacancy (V O ) transition layer (3–8 nm) at the WO 3 /solid-electrolyte interface via in situ redox reaction of silver nanowires (AgNWs) in an acidic precursor. During immersion growth, AgNWs undergo oxidation (Ag → Ag + + e − ). The liberated electrons trigger localized W 6+ reduction to W 5+ and spontaneous V O formation, establishing a gradient defect architecture that mediates an ion-coupled charge transfer (ICCT) mechanism. Temperature-dependent electrochemical impedance spectroscopy and density functional theory calculations yield a 47% reduction in interfacial activation energy (≈0.72 eV to ≈0.38 eV), closely agreeing with climbing-image nudged elastic band (CI-NEB) predictions (51% decrease). This kinetic enhancement translates into a ∼3-fold acceleration in switching speed (t c : 42.3 → 12.4 s; t b : 31.8 → 8.7 s), directly confirming that the V O gradient converts a barrier-dominated interface into a kinetically facile charge-transfer junction. The optimized all-solid-state device delivers a near-infrared transmittance modulation of 91.2% at 1100 nm and retains >85% of its initial modulation after 10,000 consecutive switching cycles. Post-cycling focused ion beam scanning electron microscopy confirms an atomically intact, delamination-free interface, evidencing the chemo-mechanical resilience imparted by the V O gradient. The ICCT-enabled wet-chemical route scales to uniformly colored 10 × 10 cm 2 devices. Outdoor field tests demonstrate a peak indoor cooling capacity of ≈9.5 °C, while EnergyPlus simulations across 40 global cities project annual energy savings of ≈140 MJ m −2 in tropical regions. This work establishes gradient oxygen vacancy–mediated ICCT as a quantitative and generalizable paradigm for engineering solid–solid interface kinetics, enabling ultra-stable all-solid-state electrochromic smart windows for next-generation adaptive building envelopes.