Abstract Flexible electrochromic devices are promising for wearable electronics, smart windows, and adaptive displays. However, their performance and stability are often limited by the narrow electrochemical stability windows of plastic‐based flexible substrates. Here a flexible ECD is presented that employs a photocurable redox‐active semi‐solid electrolyte incorporating a bromide (Br − /Br 3 − ) redox mediator. Combined with inkjet‐printed WO 3 electrodes and activated carbon electrodes on flexible ITO/PET substrates, the developed device demonstrates significant optical contrast (≈67%) and exceptional mechanical durability, retaining ≈99% of optical modulation after 1000 bending cycles. In a small‐scale house model under AM1.5G simulated sunlight, the device simultaneously modulated light and heat, demonstrating thermal‐ management efficacy for smart‐window applications. Crucially, systematic electrode potential tracking coupled with ex situ X‐ray photoelectron spectroscopy analysis provides explicit and quantitative correlations between the mediator's redox potentials, electrode‐specific reactions, and optical modulation. These mechanistic insights offer clear design guidelines for electrolytes and electrodes optimized for flexible devices operating within restricted voltage windows.
Park et al. (2025) studied this question.