Optimizing thermal annealing temperatures towards improved and stable electrochromic polymeric films and devices

•Thermal annealing (TA) temperature influences the morphology of the electrochromic films.•The effective overpotential can be correlated to thermal annealing (TA) temperature.•TA temperature greatly affects the electrochromic device (ECD) performances.•The optimized ECD exhibits an excellent optical memory capability. The preparation process plays a significant role in manipulating the morphology of organic electrochromic polymer (ECP) films, thus improving the stability of the prepared devices. In this work, the influence of thermal annealing (TA) temperatures on ECP films has been systematically investigated. The relationship between the TA temperature and the effective overpotential was determined. It was found that the TA temperature is critical for achieving the desired morphology of ECP film. At the optimized TA temperature of 180 °C, electrochromic devices (ECDs) with excellent reversibility were obtained. The response speed of the solid-state device with optimized TA temperature was more than two times faster than the unoptimized one. The coloring efficiency was also significantly enhanced, reaching the value of 374 cm2/C. Notably, the ECD based on the optimal TA temperature also showed surprisingly excellent stability, maintaining its bleaching state for almost two weeks with only a slight deterioration in the visible state.