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A family of dioxythiophene (DOT)-based conjugated random copolymers, capable of reversibly switching between a neutral black and an oxidized transmissive state, are reported for electrochromic (EC) applications. By replacing 3,4-ethylenedioxythiophene (EDOT) in the previous generation of a core donor–acceptor–donor (D–A–D) terheterocycle with a methyl-alkylated 3,4-propylenedioxythiophene (ProDOT), we enhance the solubility of precursors and monomers in this new generation of broadly absorbing electrochromic polymers (ECPs). By adjusting the newly designed terheterocycle monomer feed ratio, we obtain three polymers with varying hues of color neutrality (a* and b* < ±10) throughout the entire switching voltage range and with integrated contrasts 45–49% throughout the visible region (380–700 nm). The a* values of the polymers ranged between −8 (green hue) and +5 (red hue), with their b* values ranging between −4 and −7 (blue hue) in their neutral states; additionally, the a* and b* values are all below ±8 in their oxidized states. In electrochromic devices (ECDs), we exploit this variation in color hue to achieve color balance with the counter electrode material—a minimal color-changing polymer (MCCP) that is colorless in its fully neutral and oxidized states but light red at intermediate potentials. This red hue was balanced by the green hue of ECP–Random40, leading to an ECD that was color-neutral (a* ranging from −0.8 to −11 and b* ranging from −0.5 to 1.7) throughout the switching voltage range. This family of high-contrast and color-neutral ECPs are scalable with high yielding syntheses for all monomers due to the enhancement of monomer solubility and the usage of commonly available DOT moieties, which will aid in advancing the development of large-scale polymer-based EC window and display applications. This method provides materials that switch from black to transmissive through only gray intermediates as needed for switchable color tinting applications.

The design of high bandgap electrochromic polymers (ECPs) that switch from a high energy absorbing colored state to a near-IR absorbing colorless state requires a challenging balance to be struck between achieving large changes in the absorption profile while maintaining sufficiently low oxidation potentials for use in full-color electrochromic devices. Previous studies on high bandgap ECPs have investigated structure–property relationships in dioxythiophenes copolymerized with various arylenes. Here, we expand this understanding by looking more closely at the effect of the dioxythiophene moiety as well as by varying the substituents on the arylene moiety. Three ECPs have been synthesized to perform this study with repeat units composed of electron-rich dimethoxyphenylene in alternation with dimers of 3,4-dialkoxy- and 3,4-propylenedioxythiophenes, yielding high gap polymers that are vibrant yellow or orange in the charge neutral state. Comparing these newly synthesized polymers to a structurally similar set previously reported, we elucidate the subtle steric and electronic effects that govern bandgap and redox properties in dioxythiophene copolymers.

To achieve optimal performance in a conjugated polymer-based electrochemical device, i.e. for a supercapacitor to reach full depth of discharge or for an electrochromic device (ECD) to achieve maximum contrast, the two electrodes must be in different oxidation states when the device is assembled. Here, we evaluate the use of chemical oxidation as a scalable postprocessing method to adjust the redox state of polymer-coated electrodes. We evaluate how the extent of oxidation depends on both the redox properties of the conjugated polymer and on the choice of chemical oxidant, and how these parameters affect the functionality of the film. Comparing Ag(I) and Fe(III) oxidants, we find that it is not the oxidizing power that determines the extent of doping but rather the redox potentials of the polymers, with the more easily oxidized polymers doping to a higher extent. Because the polarity and surface energy of the polymer changes upon oxidation, we also show how a phosphonic acid surface pre-treatment improves interfacial adhesion between the polymer and a transparent oxide electrode (ITO). Finally, as a proof of principle, we demonstrate how chemical oxidation of the organic counter electrode a minimally color changing dioxypyrrole polymer enhances the device contrast of an ECD, confirming that this approach is a promising route toward high-throughput manufacturing of ECDs and other polymer-based electrochemical devices.