Conjugated electrochromic (EC) polymers for flexible EC devices (ECDs) generally lack a fully colorless bleached state. A strategy to overcome this drawback is the implementation of a new sidechain‐modified poly(3,4‐ethylene dioxythiophene) derivative that can be deposited in thin‐film form in a customized high‐throughput and large‐area roll‐to‐roll polymerization process. The sidechain modification provides enhanced EC properties in terms of visible light transmittance change, Δτ_v = 59% (ΔL* = 54.1), contrast ratio (CR = 15.8), coloration efficiency (η = 530 cm² C⁻¹), and color neutrality (L* = 83.8, a* = −4.3, b* = −4.1) in the bleached state. The intense blue‐colored polymer thin films exhibit high cycle stability (10 000 cycles) and fast response times. The design, synthesis, and polymerization of the modified 3,4‐ethylene dioxythiophene derivative are discussed along with a detailed optical, electrochemical, and spectroelectrochemical characterization of the resulting EC thin films. Finally, a flexible see‐through ECD with a visible light transmittance change of Δτ_v = 47% (ΔL* = 51.9) and a neutral‐colored bleached state is developed.

Large‐area electrochromic devices (ECDs) based on a cathodically‐coloring, side chain‐modified poly(3,4‐ethylene dioxythiophene) (PEDOT) derivative and anodically‐coloring Prussian blue (PB) are assembled by a customized sheet‐to‐sheet (S2S) lamination process. The ECDs with two complementary switching “half‐cells”, based on flexible PET‐ITO substrates, offer enhanced optical properties in terms of visible light transmission change (4–53%), contrast ratio (CR = 93.4) and color neutrality (L* = 77.9, a* = −5.9, b* = −0.6) in the bleached state. The cycling stability is monitored for up to 10 000 switching cycles (97% charge retention). The reported optical, electrochemical, and in operando (in situ) spectroelectrochemical data are obtained from small laboratory‐scale ECDs (active area: 5 × 5 cm²). These results, the homogeneity of the large‐area devices and the scalability of the S2S lamination process are confirmed by measurements on the large ECDs with an active area of 45 × 65 cm². This large‐area electrochromic film technology with high optical contrast and enhanced cycling stability offers an excellent perspective for further development and scale‐up towards pilot production and the commercialization of flexible ECDs upon their unique materials and processing characteristics.

We present the optical, electrochemical, and electrochromic properties of Fe(II)-, Co(II)- and Ru(II)-based metallo-supramolecular polymers (MEPEs) self-assembled from rigid, π-conjugated bis-terpyridines with different numbers of pyridine linkers. By exciting the metal-to-ligand charge transfer (MLCT) transition, Ru-MEPEs show a weak luminescence in the NIR region (λ_lum = 765 nm) at room temperature. The viscosity of Co-MEPEs in water, ethanol and 75% acetic acid is significantly higher in comparison to the analogous Fe-MEPEs. The SEM cross-section images of the highly transparent dip-coated films show smooth and homogenous surfaces with film thicknesses of <200 nm for Fe-, Co- and Ru-MEPEs. The cyclic voltammograms of the Fe- and Ru-MEPEs show a reversible redox couple corresponding to the Fe(II)/Fe(III) and Ru(II)/Ru(III) states, respectively. Co-MEPEs display two metal centered Co(II)/Co(I) and Co(II)/Co(III) reversible redox waves at −1.12 and −0.10 V vs. Fc/Fc⁺, respectively. Fe-MEPE films show a promising high cycle stability over 1000 switching cycles. The coloration efficiencies were also determined for Fe-MEPEs (720 mC cm⁻² at 594 nm). The study of the electrochromic properties reveals that the introduction of pyridine linkers enhances the switching stability and reversibility. Co-MEPEs exhibit a broad absorption band covering the visible and NIR region at a negative potential (−1.4 V vs. Fc/Fc⁺) due to the metal-to-ligand charge transfer from Co(I) to the acceptor terpyridine ligands.