Electrochromic organic and polymeric materials for display applications

An electrochromic material is one where a reversible color change takes place upon reduction (gain of electrons) or oxidation (loss of electrons), on passage of electrical current after the application of an appropriate electrode potential. In this review the general field of electrochromism is introduced, with coverage of the types, applications, and chemical classes of electrochromic materials and the experimental methods that are used in their study. The main classes of electrochromic organic and polymeric materials are then surveyed, with descriptions of representative examples based on transition metal coordination complexes, viologen systems, and conducting polymers. Examples of the application of such organic and polymeric electrochromic materials in electrochromic displays are given

Optimization of PEDOT Films in Ionic Liquid Supercapacitors: Demonstration As a Power Source for Polymer Electrochromic Devices

We report on the optimization of the capacitive behavior of poly­(3,4-ethylenedioxythiophene) (PEDOT) films as polymeric electrodes in flexible, Type I electrochemical supercapacitors (ESCs) utilizing ionic liquid (IL) and organic gel electrolytes. The device performance was assessed based on figures of merit that are critical to evaluating the practical utility of electroactive polymer ESCs. PEDOT/IL devices were found to be highly stable over hundreds of thousands of cycles and could be reversibly charged/discharged at scan rates between 500 mV/s and 2 V/s depending on the polymer loading. Furthermore, these devices exhibit leakage currents and self-discharge rates that are comparable to state of the art electrochemical double-layer ESCs. Using an IL as device electrolyte allowed an extension of the voltage window of Type I ESCs by 60%, resulting in a 2.5-fold increase in the energy density obtained. The efficacies of tjese PEDOT ESCs were assessed by using them as a power source for a high-contrast and fast-switching electrochromic device, demonstrating their applicability in small organic electronic-based devices

An Electrochromic Painter’s Palette: Color Mixing via Solution Co-Processing

Electrochromic polymers (ECPs) have been shown to be synthetically tunable, producing a full palette of vibrantly colored to highly transmissive polymers. The development of these colored-to-transmissive ECPs employed synthetic design strategies for broad color targeting; however, due to the subtleties of color perception and the intricacies of polymer structure and color relationships, fine color control is difficult. In contrast, color mixing is a well-established practice in the printing industry. We have identified three colored-to-transmissive switching electrochromic polymers, referred to as ECP-Cyan (ECP-C), ECP-Magenta (ECP-M), and ECP-Yellow (ECP-Y), which, via the co-processing of multicomponent ECP mixtures, follow the CMY color mixing model. The presented work qualitatively assesses the thin film characteristics of solution co-processed ECP mixtures. To quantitatively determine the predictability of the color properties of ECP mixtures, we estimated mass extinction coefficients (ε_mass) from solution spectra of the CMY ECPs and compared the estimated and experimentally observed color values of blends via a calculated color difference (Δ<i>E</i>_ab). The values of Δ<i>E</i>_ab range from 8 to 26 across all mixture compositions, with an average value of 15, representing a reasonable degree of agreement between predicted and observed color values. We demonstrate here the ability to co-process ECP mixtures into vibrantly colored, visually continuous films and the ability to estimate the color properties produced in these mixed ECP films

Follow the Yellow Brick Road: Structural Optimization of Vibrant Yellow-to-Transmissive Electrochromic Conjugated Polymers

A series of conjugated polymers were designed and synthesized to extract structure–property relationships with the goal of yielding yellow-to-transmissive switching electrochromes. The polymers are based on repeat units of propylenedioxythiophene (ProDOT) in alternation with a variety of arylenes including 1,4-phenylene (ProDOT-Ph), 2,7-fluorene (ProDOT-Fl), 2,7-carbazole (ProDOT-Cbz), 2,5-dimethoxy-1,4-phenylene (ProDOT-Ph­(MeO)₂), and 2,7-pyrene (ProDOT-Py). Additionally, a random copolymer containing ProDOT and two different arylene units was produced: ProDOT-phenylene-ProDOT-dimethoxyphenylene (R-ProDOT-Ph/Ph­(MeO)₂) and two polymers with a ProDOT dimer in alternation with pyrene and phenylene composed ProDOT₂-pyrene (ProDOT₂-Py) and ProDOT₂-phenylene (ProDOT₂-Ph), respectively. The polymers were synthesized using Suzuki polycondensation. Examinations of the optoelectronic properties via UV–vis–NIR spectroscopy, differential pulse voltammetry, and spectroelectrochemistry show that varying the electron richness of the polymer by utilizing more electron rich arylenes, dimers of ProDOT, or less electron rich arylenes, the oxidation potential could be decreased or increased, respectively, ranging from 270 to 650 mV. Through subtle C–H <i>ortho</i> interactions from the arylene unit, yellow neutral state colors were maintained with transmissive or near-transmissive oxidized states. Colorimetry utilizing <i>L</i>*<i>a</i>*<i>b</i>*, where <i>a</i>*<i>b</i>* values correlate to the chroma or saturation of a color (note: −<i>a</i>* and +<i>a</i>* correspond to green and red and −<i>b</i>* and +<i>b</i>* correspond to blue and yellow, respectively) and <i>L</i>* represents the lightness, was used to show the maintenance of yellow colors in the neutral states. Herein, the yellow polymers had <i>L</i>* values above 84.0, <i>a</i>* values ranging from −11.6 to 24.8, and <i>b</i>* values greater than 47.6. In the oxidized states, the most transmissive forms had <i>L</i>* values above 70.0, <i>a</i>* values ranging from −2.1 to 2.0, and <i>b</i>* values ranging from −6.8 to −0.1. These structure–property relationships grant access to conjugated polymers with high energy absorbance in the visible, while allowing variability in redox potentials, providing a deeper understanding in yielding yellow-to-transmissive electrochromic polymers

Poly[Bis-EDOT-Isoindigo]: An Electroactive Polymer Applied to Electrochemical Supercapacitors

Poly­[6,6′-bis­(ethylene-3,4-dioxythien-2-yl)]-<i>N</i>,<i>N</i>′-dialkylisoindigo (PBEDOT-iI) was synthesized and incorporated as an electroactive material into electrochemical supercapacitors (ESCs) in type I and type III configurations. In type I ESCs, PBEDOT-iI provides a specific power of ∼360 W/kg and specific energy of ∼0.5 Wh/kg, while retaining about 80% of its electroactivity over 10 000 cycles. In addition, we report on the use of PBEDOT-iI in type III supercapacitors where operating voltages as high as 2.5 V were achieved with specific energies of ca. 15 Wh/kg, albeit with limited stability