Electrochemical study of dual conjugated polymer electrochromic devices

A multi-chromic supercapacitor of high coloration efficiency integrating a MOF-derived V2O5 electrode

Modern technological trends in smart electronic devices demand more intelligent automation. Simultaneous integration of energy storage and multicolor electrochromism in a single device improves user-device interfacing based on a salient human-readable output. In this work, primarily metal-organic framework (MOF) derived V₂O₅ was synthesized which, as an electrochromic material, shows high optical modulation of 35% at 485 nm, with very fast switching speeds (2.9/3.4 s for coloring/bleaching). The multiple coloration states of the V₂O₅ electrode make it worthy for further integration as a smart negative electrode in a multicolored electrochromic asymmetric supercapacitor, where the electrochromic polyaniline electrode serves as the counter electrode. The device demonstrates a high coloration efficiency of 137.2 cm² C^-1 and an areal capacitance of 12.27 mF cm^-2 and an energy density of 2.21 × 10^-3 mW h cm^-2 at a current density of 0.05 mA cm^-2. By virtue of its different chromatic states during charging and discharging, smart visual tracking of the state of charge of the supercapacitor can be realized. Such a design of energy storage devices will have promising practical application in futuristic smart multifunctional electronic devices.

Reliable, High-Performance Electrochromic Supercapacitors Based on Metal-Doped Nickel Oxide

Herein, high-performance, reliable electrochromic supercapacitors (ECSs) are proposed based on tungsten trioxide (WO₃) and nickel oxide (NiO) films. To maximize device performance and stability, the stoichiometric balance between anode and cathode materials is controlled by carefully adjusting the thickness of the anodic NiO film while fixing the thickness of WO₃ to ∼660 nm. Then, a small amount (≤10 mol %) of metal (e.g., copper) is doped into the NiO film, improving the electrical conductivity and electrochemical activity. At a Cu doping level of 7 mol %, the resulting ECS exhibited the highest performance, including a high areal capacitance (∼14.9 mF/cm²), excellent coulombic efficiency (∼99%), wide operating temperature range (0-80 °C), reliable operation with high charging/discharging cyclic stability (>10,000 cycles), and good self-discharging durability. Simultaneously, the change in transmittance of the device is well synchronized with the galvanostatic charging/discharging curve by which the real-time energy storage status is visually indicated. Furthermore, the practical feasibility of the device is successfully demonstrated. These results imply that the ECS fabricated in this work is a promising potential energy storage platform and an attractive component for future electronics.

Broad spectrum absorption and low-voltage electrochromic operation from indacenodithieno[3,2-b]thiophene-based copolymers

The design and application of IDTT-based conjugated polymers for red-to-transparent and black-to-transparent electrochromic switching at low voltages are reported.

Highly Transparent Crosslinkable Radical Copolymer Thin Film as the Ion Storage Layer in Organic Electrochromic Devices

A highly transparent crosslinkable thin film made of the radical polymer poly(2,2,6,6-tetramethyl-4-piperidinyloxy methacrylate)- co-(4-benzoylphenyl methacrylate) (PTMA- co-BP) has been developed as the ion storage layer in electrochromic devices (ECDs). After photo-crosslinking, the dissolution of PTMA- co-BP in electrolytes was mitigated, which results in an enhanced electrochemical stability compared with the homopolymer PTMA thin film. Moreover, the redox capacity of PTMA- co-BP increased because of the formation of a crosslinked network. By matching the redox capacity of the PTMA- co-BP thin film and bis(alkoxy)-substituted poly(propylenedioxythiophene), the ECD achieved an optical contrast of 72% in a small potential window of 2.55 V (i.e., switching between +1.2 and -1.35 V), and it was cycled up to 1800 cycles. The ECD showed an excellent optical memory as its transmittance decayed by less than 3% in both the colored and bleached states while operating for over 30 min under open-circuit conditions. Use of crosslinkable radical polymers as the transparent ion storage layer opens up a new venue for the fabrication of transmissive-mode organic ECDs.

High Performance and Long-Term Stability in Ambiently Fabricated Segmented Solid-State Polymer Electrochromic Displays

This work reports on the performance of a segmented polymer electrochromic display that was fabricated with solution-based processes in ambient atmosphere. An encapsulation process and the combination of structured wells for the polymer electrochrome and electrolyte layers as well as the use of a preoxidized counter polymer yields high contrasts and fast switching speeds. Asymmetric driving-with respect to time-of the display is investigated for the first time and the degradation effects in the electrochrome layer are analyzed and addressed to yield a stable device exceeding 100,000 switching cycles. A printed circuit board was integrated with the display, allowing the device to be run as a clock, where the segments only required short pulses to switch without the need for a constant current to maintain its state. Such an application pairs well with the advantages of electrochromic polymers, drawing on its high contrast, stability, and ability to maintain its colored or colorless state without the need for a constant power supply, to demonstrate the promise as well as the challenges of developing more sophisticated electrochromic devices.

From the bottom up--flexible solid state electrochromic devices

Solid-state flexible polymer-based electrochromic devices are fabricated continuously by stacking layers in one direction. This novel bottom-up approach with no need for a lamination step is realized through in situ photo-crosslinking of the electrolyte using a "curing-chamber" fitted to a roll-coater, which lowers the oxygen concentration at the electrolyte surface. This enables fully printed and 2D patterned organic electrochromics.

Color combination of conductive polymers for black electrochromism

Conducting polymers that absorb three primary colors, red, green, and blue (RGB), were introduced with a yellow electrochromic polymer (Y) for the preparation of black electrochromic devices. Red poly(3-hexylthiophene) (P3HT) and blue poly(3,4-ethylenedioxythiophene) (PEDOT) were coated on one side of the electrode as a cathodically coloring electrochromic (EC) layer, while green poly(aniline-N-butylsulfonate) (PANBS) and yellow EC poly{[1,3-bis(9',9'-dihexylfluoren-20-yl)azulenyl]-alt-[2",7"-(9",9"-dihexylfluorenyl]} (PDHFA) were coated on the opposite electrode to complete a complementary EC device. The yellow PDHFA layer effectively compensated for absorption below 450 nm and above the 600 nm region, which was lacking in the RGB electrode. The resultant RGBY ECD provided a black color near the CIE black with L*, a*, and b* values of 32, -1.1, and 3.7, respectively, covering a broad absorption in the visible range in the colored state. The state of the black EC device was maintained, even after the electricity was turned off for 200 h, showing stable memory effect.

Electrochromic conducting polymers: optical contrast characterization of chameleonic materials

The optical characterization in the visible wavelength range was obtained for an electrochromic material, poly-3, 4-ethylenedioxy-thiophene (PEDOT), as a function of its redox charge density (charge consumed for the color change between its maximum and minimum absorbance states). The experimental procedure was kept very simple and all the information can be obtained from only one film, including the identification of the maximum achievable contrast for the material. Different films of the electrochromic material were tested in order to check the validity of the predicted values, showing excellent agreement.