Process controlled performance for soluble electrochromic polymers

Abstract We present a method that can be used to quantify and optimize the performance of electrochromic polymers and evaluate how the choice of coating method affects the film characteristics. The mathematical approach, together with a standard experimental procedure to perform it, is described. This method can be applicable to any electrochromic material and deposition technique with the only requirement being that the Beer–Lambert law is followed. Three common (and industrially applicable) coating techniques (namely spray, blade and spin coating), together with three solution processable electrochromic polymers (ECP-Magenta, ECP-Black and ECP-Cyan), were used in the study to illustrate the feasibility of this method. For all the evaluated polymers, the choice of deposition method had a direct effect on the maximum achievable contrast. Spin coated films tended to show the highest contrasts, closely followed by blade coated films and finally spray coated films. When explaining those differences we showed that coloration efficiency, widely used as an electrochromic quality parameter, is not directly related to achievable contrast values. Instead, we have proposed the volumetric redox density. It has been found that higher values of this magnitude translate into higher achievable contrasts.