Composite Coloration Efficiency Measurements of Electrochromic Polymers Based on 3,4-Alkylenedioxythiophenes

We report a method to measure the composite coloration efficiency of organic electrochromic polymers at 95% of the total optical density change measured at λmax. This practical method is useful for the comparison of organic polymers as well as inorganic electrochromic oxides and for gaining insights into the reasons for increased efficiencies in organic polymer systems. Three polymers from the family of the poly(3,4-alkylenedioxythiophenes) (PXDOTs) were chosen, due to their well-behaved electrochromic properties, to develop the tandem chronoabsorptometry/chronocoulometry method. Coloration efficiencies were measured by monitoring the amount of injected/ejected charge as a function of the change in optical density of the polymer film. The results of these experiments revealed a significant relationship between structure and coloration efficiency determined at λmax in organic polymers. Poly(3,3-dimethyl-3,4-dihydro-2H-thieno[3,4-b]dioxepine) (PProDOT-Me2) possessed the highest coloration efficiency (375 cm2/C) compared to poly(3,4-ethylenedioxythiophene) (PEDOT) (183 cm2/C) and poly(3,4-propylenedioxythiophene) (PProDOT) (285 cm2/C), due to a combination of larger changes in optical density at λmax and higher doping levels.