Synergistic Optimization of High Output and Long-Term Stability in Fully Printed PEDOT:PSS-Based Electrochromic Devices by Patterned Carbon-Wire Grids

The electrochromic output and long-term cycling stability of electrochromic devices (ECDs) are governed not only by ion transport but also by the in-plane spatial distribution of electronic current-collecting boundaries. In this work, fully printed ECDs were fabricated by introducing a patterned carbon-wire grid between the lower PEDOT:PSS layer and the carbon electrode. The geometric characteristics of this bottom current-collecting structure were uniformly quantified by the parameter S / L, defined as the ratio of the carbon-covered area S to the total edge perimeter L of the carbon wires. T-type devices (powered by T-shaped carbon electrodes) and F-type devices (powered by a full-area continuous bottom carbon electrode) served as two reference configurations. Compared with T-type devices, the carbon-wire-grid devices markedly improved the in-plane uniformity of the electrochemical driving force while maintaining strong electrochromic performance without using a full-area continuous electrode. At S / L = 0.126 mm, the device delivered a current density of 1.523 mA/cm 2, an injected charge of 0.940 mC/cm 2, and an optical density change ΔOD = 0.514, representing improvements of 59%, 23%, and 10%, respectively. The transmission line model (TLM) yielded an effective transfer length L T = 0.0712 mm, from which the critical design criterion ( S / L ) critical = 0.1252 mm was derived. This value marks the threshold at which device performance transitions from continuous enhancement to a plateau-like behavior. After 2500 cycles, the representative carbon-wire-grid device retained the highest postcycling ΔOD = 0.482 and exhibited lower output decay than the F-type device. These results demonstrate that patterned carbon-wire grids provide an effective route for balancing electrochromic performance and long-term stability in ECDs.