Printed Multicolor High-Contrast Electrochromic Devices

In this study, electrochemical responses of inkjet-printed multicolored electrochromic devices (ECD) were studied to evaluate the feasibility of presenting multiple colors in one ECD. Metallo-supramolecular polymers (MEPE) solutions with two primary colors were inkjet-printed on flexible electrodes. By digitally controlling print dosages of each species, the colors of the printed EC thin film patterns can be adjusted directly without premixing or synthesizing new materials. The printed EC thin films were then laminated with a solid transparent thin film electrolyte and a transparent conductive thin film to form an ECD. After applying a dc voltage, the printed ECDs exhibited great contrast with a transmittance change (Δ<i>T</i>) of 40.1% and a high coloration efficiency of 445 cm² C^–1 within a short darkening time of 2 s. The flexible ECDs also showed the same darkening time of 2 s and still had a high Δ<i>T</i> of 30.1% under bending condition. This study demonstrated the feasibility to fabricate display devices with different color setups by an all-solution process and can be further extended to other types of displays

Thermally Cured Dual Functional Viologen-Based All-in-One Electrochromic Devices with Panchromatic Modulation

Vinyl benzyl viologen (VBV) was synthesized and utilized to obtain all-in-one thermally cured electrochromic devices (ECDs). The vinyl moiety of VBV monomer could react with methyl methacrylate (MMA) to yield bulky VBV/poly­(methyl methacrylate) (PMMA) chains and even cross-linked network without the assistance of additional cross-linker. Both the bulky VBV/PMMA chains and the resulting polymer network can hinder the aggregation of the viologens and reduce the possibility of dimerization, rendering enhanced cycling stability. Large transmittance changes (Δ<i>T</i>) over 60% at both 570 and 615 nm were achieved when the VBV-based ECD was switched from 0 V to a low potential bias of 0.5 V. Ultimately, the dual functional of VBV molecules, serving simultaneously as a promising electrochromic material and a cross-linker, is fully utilized in the proposed electrochromic system, making its fabrication process much easier. Negligible decays in Δ<i>T</i> at both wavelengths were observed for the cured ECD after being subjected to 1000 repetitive cycles, while 17.1% and 22.0% decays were noticed at 570 and 615 nm, respectively, for the noncured ECD. In addition, the low voltage-driven feature of the VBV-based ECD enables it to be incorporated with phenyl viologen (PV), further expanding the absorption range of the ECD. Panchromatic characteristic of the proposed PV/VBV-based ECD was demonstrated while exhibiting Δ<i>T</i> over 60% at both wavelengths. Only 5.3% and 6.9% decays, corresponding at 570 and 615 nm, respectively, were observed in the PV/VBV-based ECD after 10 000 continuous cycles at bleaching/coloring voltages of 0/0.5 V with an interval of 10 s for both bleaching and coloring processes

Achieving Low-Energy Driven Viologens-Based Electrochromic Devices Utilizing Polymeric Ionic Liquids

Herein, three kinds of viologens-based electrochromic devices (ECDs) (heptyl viologen (HV­(BF₄)₂), octyl viologen (OV­(BF₄)₂), and nonyl viologen (NV­(BF₄)₂)) were fabricated utilizing ferrocene (Fc) as a redox mediator. Among them, the NV­(BF₄)₂-based ECD exhibits the highest coloration efficiency (36.2 cm²/C) owing to the lowest driving energy. Besides, switching between 0 and 1.2 V, the NV­(BF₄)₂-based ECD shows a desirable initial transmittance change (Δ<i>T</i> = 56.7% at 605 nm), and long-term stability (Δ<i>T</i> = 45.4% after 4000 cycles). Furthermore, a UV-cured polymer electrolyte containing polymeric ionic liquid (PIL, 1-allyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide) and ethoxylated trimethylolpropane triacrylate (ETPTA) was introduced to the NV­(BF₄)₂-based ECD. By controlling the weight percentage of the PIL, different curing degrees of the polymer electrolytes were obtained and led to an improved stability of the NV­(BF₄)₂-based ECD because of the immobilization of NV­(BF₄)₂. This observation was explained by calculating the apparent diffusivity (<i>D</i>_app) of the redox species in the NV­(BF₄)₂-based ECD under various curing degrees. In addition, increasing the amount of PIL leads to a lower driven energy needed for the NV­(BF₄)₂-based ECD, following the same trend as the value of <i>D</i>_app. Among all NV­(BF₄)₂-based ECDs, 20 wt % of PIL addition (20-PIL ECD) exhibits large transmittance change (Δ<i>T</i> = 55.2% at 605 nm), short switching times (2.13 s in coloring and 2.10 s in bleaching), high coloration efficiency (60.4 and 273.5 cm²/C at 605 nm, after excluding the current density at the steady state), and exceptional cycling stability (Δ<i>T</i> = 53.8% after 10,000 cycles, or retained 97.5% of its initial Δ<i>T</i>)