Unraveling and Mitigating Resolution Loss in UV‐Assisted Vapor Phase Polymerization of Monolithic PEDOT:Tosylate Electrochromic Patterns

The conducting polymer poly(3,4‐ethylenedioxythiophene) (PEDOT) is well known for its fast and stable electrochromism. Recently, a patterning concept was developed in which ultraviolet (UV) light exposure modifies the growth rate of its p‐toluenesulfonate derivative (PEDOT:Tos) during oxidative vapor phase polymerization, enabling continuous films with electrochromic patterns that can switch without supporting electrodes. However, the resulting contrast often deviates significantly from the intended exposure design, previously believed to originate from diffusion of mobile water. This study investigates that hypothesis by comparing oxidant blends containing short and long block copolymers (Pluronic L‐31 and P‐123), expected to create oxidant templates with different properties. Fourier‐transform infrared spectroscopy reveals strong signatures of loosely bound water after UV exposure for all formulations, which diffuses transiently along the exposure boundary. Yet, the findings show that linewidth broadening does not correlate with diffusion but rather with additional macroscopic structuring outside the exposure boundary, which is absent at low (5 wt.%) block‐copolymer concentration. Formulations with Pluronic L‐31 provide a resist‐free approach for achieving 2–3 µm electrochromic resolution in a standalone PEDOT:Tos film achieving switching times below 400 ms in aqueous electrolyte, and sustaining 2500 switching cycles in propylene glycol‐based polyelectrolyte.