Fine-Tuning the Color Hue of π-Conjugated Black-to-Clear Electrochromic Random Copolymers

Abstract

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.

Advanced developments in nonstoichiometric tungsten oxides for electrochromic applications

“…Polymer-based EC materials targeting visible light offer several potential advantages with good absorption properties in a wide range of colors, faster switching speed, and higher coloration efficiency, which are usually difficult to achieve with metal oxides. [43][44][45] Based on the design of the donor-acceptor (D-A) structure, 46,47 EC polymers with lower onset potential and higher reversible-switching stability including conjugated polymers, 44,[48][49][50] unconjugated polymers, 51 7 and cross-conjugated polymers have been demonstrated. [52][53][54] Poly (3-hexylthiophene) (P3HT) is a regioregular semiconducting polymer that shows EC modulation under a small electrical bias polarities and acts as an anodically coloring material.…”

Highly Stable Indacenodithieno[3,2-b]thiophene-Based Donor–Acceptor Copolymers for Hybrid Electrochromic and Energy Storage Applications

“…To the best of our knowledge, these values rank to the top of all-polymer electrochromic supercapacitors 38 , 48 , 63 and among the best-performing black-to-transparent and colored-to-transparent electrochromic polymers. 27 , 33 , 64 The record η values are more than three times higher for conventional electrochromic polymers, which stem from their approximately three times lower charge densities compared to the IDTT-based polymers in this study. 79 …”

“…The vast majority of electrochromic polymers are based on 3,4-ethylenedioxythiophene (EDOT) and similar dioxythiophene building blocks because of their low oxidation potential, fast color switching, and relatively simple chemical structures that allow easy color tuning, as spearheaded by the Reynolds group. 23 − 27 Other groups have developed similar structures to further tune the doping characteristics, optical contrast, and color purity of the polymers, for example, by means of chemical doping and electropolymerization. 28 − 31 However, polymers based on the EDOT and dioxythiophene structures are often identified by a blue transmission window in their neutral state or remaining absorption band in the low-energy visible spectral region, causing a characteristic blue tint to the oxidized state.…”

D‐A type hybrid polymers based on EDOT and various benzodiazoles for electrochromic materials

“…When the electron‐withdrawing unit is combined with EDOT, the resulting polymer has lower optical band gap and better stability 8–11 . On the other hand, benzothiadiazole and its derivatives have strong electron‐withdrawing structures and have been widely used in D‐A type conjugated polymers 12–15 . And the introduction of appropriate long alkyl side chains in the donor and acceptor units can not only effectively improve the solubility, but also affect the electronic properties such as optical band gap, oxidation potential and stability.…”