Organic Electrochromic Devices Research Articles

Greyscale and Paper Electrochromic Polymer Displays by UV Patterning.

Electrochromic devices have important implications as smart windows for energy efficient buildings, internet of things devices, and in low-cost advertising applications. While inorganics have so far dominated the market, organic conductive polymers possess certain advantages such as high throughput and low temperature processing, faster switching, and superior optical memory. Here, we present organic electrochromic devices that can switch between two high-resolution images, based on UV-patterning and vapor phase polymerization of poly(3,4-ethylenedioxythiophene) films. We demonstrate that this technique can provide switchable greyscale images through the spatial control of a UV-light dose. The color space was able to be further altered via optimization of the oxidant concentration. Finally, we utilized a UV-patterning technique to produce functional paper with electrochromic patterns deposited on porous paper, allowing for environmentally friendly electrochromic displays.

Retraction of "Single Polymeric Template-Based Full-Color Organic Electrochromic Device".

With low-cost and simple processing, organic electrochromic polymers have attracted considerable attention as a promising material platform for flexible and low-energy-consuming optoelectronic devices. However, typical electrochromic polymers can only be switched from natural-colored to oxidized-transparent states. As a result, the complexity of combining several distinct polymers to achieve a full-color gamut has significantly limited the niche applications of electrochromic polymers. Here we report an electrochromic polymer based on 4,7-di((3,3-dimethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine-3-yl)-3,4-ethylenedioxythiophene) (PEP), which exhibits fast full-color reversible tuning capability and good stability. Furthermore, a red-green-blue flexible electrochromic device just based on poly(PEP) was fabricated, which offers an effective approach to dynamically manipulate color and enables a variety of optoelectronic applications.

A highly bendable transparent electrode for organic electrochromic devices

Abstract In this article, we report a thin film of polyaniline (PANI)-grafted single-walled/double-walled carbon nanotubes (CNTs) on polyethylene terephthalate (PET) as a transparent electrode for highly bendable electrochromic films. Our results show that the high conductivity of the PANI-CNT/PET electrode brought by its conductive CNT network, as well as the strong conjugation between CNTs and PANI, can be well retained even after 9000 cycles of bending with a bending radius of 0.6 cm, which is superior to that of the most widely used transparent electrode, indium tin oxide (ITO) on PET. By electrodeposition of PANI on the PANI-CNT/PET electrode, the overall electrochromic performance of the PANI-deposited PANI-CNT/PET (PANI/PANI-CNT/PET) is comparable to its PANI/ITO/PET counterpart, whereas after 100 cycles of bending, PANI/PANI-CNT/PET can much better retain its initial electrochromic performance than PANI/ITO/PET. The mechanism for the enhanced bendability is studied via impedance analysis. It shows that the enhancement is mainly due to the robust interface between the PANI-based electrode and active layer. The findings provide a new avenue for rational design of highly bendable electrodes for flexible electrochromic devices.

Benzothiadiazole, hexylthiophen and alkoxy benzene based solution processable copolymer: Effect of the electron withdrawing substituents (fluorine atoms) on electrochemical, optical and electrochromic properties

Abstract 4,7-Bis(4-hexyl-5-(trimethylstannane) -2-thienyl) −2,1,3-benzothiadiazole (HTBT) coupled with 2,5-bis (decyloxy)-1,4-dibromobenzene to afford the donor-π-bridge-donor-acceptor conjugated poly (4,7-bis (4-hexyl-2-thienyl) −2,1,3-benzothiadiazole-co-p-didecyloxybenzene) (PTBTB). Further, copolymerization of fluorine-functionalized HTBT moiety with alkoxyl benzene π-bridge using Stille crossing-coupling reaction yield PTBTB-F. The optical, electrochemical, fluorescent, spectroelectrochemical and electrochromic switching properties of two polymers with different acceptors are studied in detail. Both polymers exhibit excellent solubility in conventional organic solvents, high thermal stability and favorable fluorescence properties. The combination of a strong electron withdrawing pendant group (fluorine atoms) with benzothiadiazole (BT) backbone significantly influences the electrochemical redox, optical and electrochromic behaviors of conducting polymers. The introduction of fluorine atoms to BT lead to a higher oxidation onset potential, but an improved electrochemical n-doping process. The optical band gaps (Eg) of PTBTB and PTBTB-F films are calculated to be 2.02 eV and 1.91 eV, respectively. PTBTB and PTBTB-F films exhibited obvious and reversible color switching between their neutral and oxidized states with high optical contrasts as well as favorable response times, making the polymers unique candidates for flexible organic electrochromic device applications.

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.

Multicolored, Low-Voltage-Driven, Flexible Organic Electrochromic Devices Based on Oligomers.

In this study, a series of organic conjugated oligomers containing 3,4-ethylenedioxythiophene (EDOT) and aromatic groups are synthesized, which are as follows: 2,5-di(methyl benzoate)-3,4-ethylenedioxy-thiophene (1EDOT-2B-COOCH3 ), 5,5'-di(methyl benzoate)-2,2'-bi(3,4-ethylenedioxythiophene) (2EDOT-2B-COOCH3 ), 5,5″-di(methyl benzoate)-2,2':5',2″-ter(3,4-ethylenedioxythiophene) (3EDOT-2B-COOCH3 ), and 5,5″'-di(methyl benzoate)-2,2':5',2″: 5″,2″'-quater(3,4-ethylenedioxythiophene) (4EDOT-2B-COOCH3 ). Using these oligomers as active materials, flexible organic electrochromic devices are fabricated. The device structure is indium tin oxide-PET plastic slide (ITO-PET)/active layer/conducting gel/ITO-PET, and the electrochromic properties of oligomers are investigated. These oligomers exhibit reversible color changes upon electrochemical doping and dedoping. The highest optical contrast is exhibited by 4EDOT-2B-COOCH3 , which is 75.2% at 700 nm.

A novel organic electrochromic device with hybrid capacitor architecture towards multicolour representation.

Despite the application of electrochromic (EC) technologies in various optical modulating devices, the challenge to achieve multicolour EC behavior in a single device still remains. However, because almost all EC materials exhibit a single colour change, only a few organic materials are able to undergo multiple colour switching within a single device. The development of multicolour EC applications is therefore highly limited. In this research, we fabricated an EC device (ECD) with the simple hybrid capacitor architecture, i.e. with a flat ITO electrode as the working side and an ITO particle-modified electrode as the counter side. We also employed an electrolyte containing both anodic and cathodic EC materials consisting of small organic molecules. In this novel ECD, each EC material successfully undergoes individual colour switching from light yellow to light green and magenta. The mechanism of a multicolour system represents a significant breakthrough towards a full-colour ECD, thereby expanding the potential of EC technology.

Transmissive-to-Black Electrochromic Devices Based on Cross-Linkable Tetraphenylethene-Diphenylamine Derivatives

Transmissive-to-black switching organic electrochromic device based on a cross-linkable, symmetric diphenylamine derivative with a tetraphenylethene core is reported. The tetraphenylethene-diphenylamine derivative, TPOSt with thermally cross-linkable styrene end groups and the model derivative, TPOMe were synthesized as a mixture of cis- and trans- isomers by Buchwald-Hartwig amination reactions. Cross-linked films of TPOSt on ITO showed a reversible, two-electron redox peak at 0.69 V vs Ag/AgCl corresponding to the formation of TPOSt dications which exhibited an absorption spectra spanning the entire visible region and extending up to 1100 nm. Further, the electrochromic switching between a highly transmissive, light yellow colored neutral state (L*= 97, a*= -5, b*= 16) and a black coloured oxidized state (L*= 41, a*= 2, b*= 8) with high optical contrasts (up to 50%ΔT) and reasonably low switching times (<10 s) were demonstrated over 1500 cycles using a simple electrochromic device design [FTO/EC layer/ ...

Novel organic multi-color electrochromic device for e-paper application

Novel organic multi-color electrochromic device for e-paper application

Novel organic multi-color electrochromic device for e-paper application

Electrochromism is reversible color change by electrochemical reaction. In this paper, we designed novel organic electrochromic device based on bispyridinepyrrole derivatives and phenothiazine molecule. The EC properties of the devices were analyzed and discussed for the possibility to multicolor representation

The trade-off between electrochromic stability and contrast of a thiophene—Quinoxaline copolymer

The stability of organic electrochromic devices is a crucial issue for their applications. However, until now the degradation mechanism of electrochromic materials are still not fully understood especially for electrochromic conjugated polymers (ECPs). To improve device stability, intensive investigation on the degradation mechanism of ECPs is urgently needed. Here we report our study on the electrochromic degradation in a thiophene–quinoxaline copolymer: poly [2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1). The results of X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectra (UPS) and UV–vis transmission spectra reveal that there are three main factors during the electrochromic degradation of TQ1. The first one is anion (ClO4−) irreversibly deep trapped, while the second is peroxidation of the thiophene group in TQ1. Both factors reduce the conductivity and electrochromism of TQ1. The third is structural relaxation resulting lager conjugated system of TQ1 molecules in film, which is gradually developed during 400 cycling of CV at a narrow potential range (0–1V). When a potential range 0–0.7V is applied, all three factors are prohibited, no electrochromism degradation is observed anymore, although the contrast becomes smaller. Our investigation systematically discloses the degradation mechanism during the electrochemistry processing of a ECP (TQ1), demonstrating the significance of trade-off between the electrochromic stability and contrast of the ECP.

Integration of graphene sensor with electrochromic device on modulus-gradient polymer for instantaneous strain visualization

In nature, some animals change their deceptive coloration for camouflage, temperature preservation or communication. This astonishing function has inspired scientists to replicate the color changing abilities of animals with artificial skin. Recently, some studies have focused on the smart materials and devices with reversible color changing or light-emitting properties for instantaneous strain visualization. However, most of these works only show eye-detectable appearance change when subjected to large mechanical deformation (100%–500% strain), and conspicuous color change at small strain remains rarely explored. In the present study, we developed a user-interactive electronic skin with human-readable optical output by assembling a highly sensitive resistive strain sensor with a stretchable organic electrochromic device (ECD) together. We explored the substrate effect on the electromechanical behavior of graphene and designed a strategy of modulus-gradient structure to employ graphene as both the highly sensitive strain sensing element and the insensitive stretchable electrode of the ECD layer. Subtle strain (0–10%) was enough to evoke an obvious color change, and the RGB value of the color quantified the magnitude of the applied strain. Such high sensitivity to smaller strains (0–10%) with color changing capability will potentially enhance the function of wearable devices, robots and prosthetics in the future.

Interfacial redox centers as origin of color switching in organic electrochromic device

In an attempt to understand the color switching mechanism of organic electrochromic devices, live spectroscopy of a viologen based device has been done. Role of redox reactions taking place at the electrode/electrolyte interface has been identified using Raman and UV–Vis spectroscopies carried out during the device operation. In-situ Raman and transmission/absorption studies establish the origin of bias induced color change, between a transparent and navy blue color, in the electrochromic device. The origin of color change has been attributed to the bias induced redox switching between its dication and free radical forms which have different optical properties from each other. Raman spectra collected from negative and positive electrodes of the device reveal that blue color species (free radical) are present at the negative electrode which is created due to reduction of the dicationic form. In-situ UV–Vis spectra reveals that the navy blue color of the device under biased condition is not due to increase in the transparency corresponding to the blue wavelength but due to suppression of its transparency corresponding to the complementary colors as studied using a from CIE (Commission Internationale de l’Eclairge International Commission on Illumination) chart. Absorption modulation has been reported from the device with good ON/OFF contrast of the device.

In situ measurements of electrode potentials of anode and cathode in organic electrochromic devices

The in situ electrode potentials of anodes and cathodes in electrochromic (EC) devices were investigated. The solution-based 2-electrode EC device was fabricated with electrolyte solutions containing anodic and cathodic EC molecules. The electrochemical reaction in a 2-electrode EC device was controlled by the electrode reaction when electroactive molecules in smaller concentrations were used. In addition, the electrode showing less electrochemical activity in the EC device was subjected to larger overpotential under the application of a driving voltage, leading to the promotion of the redox reaction at the electrode. The results showed that the electrode potentials of the device were spontaneously regulated to facilitate both electrode reactions. It is very important to know the potential at each electrode in order to understand the reaction in detail in the 2-electrode EC device.

High Contrast Electrochromic Polymer and Copolymer Materials Based on Amide-Substituted Poly(Dithienyl Pyrrole)

Conducting polymers have attracted attention as active materials for low power consuming, flexible devices with vivid colors and simple, room temperature processing methods. However, the conductive polymers with high-contrast electrochromic properties are limited in the literature. Here we achieve high-contrast electrochromic switching by copolymerization of newly synthesized an amide substituted dithienyl pyrrole (PBA) and 3,4-ethylenedioxythiophene (EDOT). In order to obtain the best optical properties of copolymer, spectral characteristics of the synthesized copolymers with different monomer feed ratios were investigated. Both homopolymer and copolymer films exhibit well defined redox and satisfied coloration efficiency. Spectroelectrochemistry studies indicate that the P(PBA-co-EDOT) has a lower bandgap (1.67 eV) and shows the excellent optical contrast (77% of 1000 nm) and coloration efficiency (697.01 cm2 C−1). The copolymer method provides a novel way to fabricate a freestanding organic electrochromic device. Additionally, the fluorescence properties of both monomer and polymer were investigated. P(PBA) having strong emission and good solubility and also P(PBA) has the potential to be used in OLEDs.

Electrosynthesis and electrochromic properties of free‐standing copolymer based on oligo(oxyethylene) cross‐linked 2,2’‐bithiophene and 3,4‐ethylenedioxythiophene

ABSTRACTOligo(oxyethylene) chains cross‐linked 2,2’‐bithiophene (BT‐E5‐BT) has been synthesized successfully. A free‐standing copolymer film based on BT‐E5‐BT and 3,4‐ethylenedioxythiophene (P(BT‐E5‐BT‐co‐EDOT)) has been synthesized by electrochemical polymerization. The electrical conductivity of P(BT‐E5‐BT‐co‐EDOT) copolymer (16 S m−1) has improved by four orders of magnitude compared to the homopolymer of BT‐E5‐BT (P(BT‐E5‐BT), 5 × 10−3 S m−1) at room temperature. Both homopolymer and copolymer films exhibit well‐defined redox and satisfied coloration efficiency. Spectroelectrochemistry studies indicate that the P(BT‐E5‐BT‐co‐EDOT) has a lower band gap in the range of 1.83–1.90 eV and shows more plentiful electrochromic colours (green, blue, purple and salmon pink) compared with the homopolymer P(BT‐E5‐BT). The Copolymer P(BT‐E5‐BT‐co‐EDOT) shows the moderate optical contrast (26% of 480 nm) and coloration efficiency (205.41 cm−1 C−2). The copolymer method provides a novel way to fabricate a free‐standing organic electrochromic device. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1583–1592

A chameleon-inspired stretchable electronic skin with interactive colour changing controlled by tactile sensing.

Some animals, such as the chameleon and cephalopod, have the remarkable capability to change their skin colour. This unique characteristic has long inspired scientists to develop materials and devices to mimic such a function. However, it requires the complex integration of stretchability, colour-changing and tactile sensing. Here we show an all-solution processed chameleon-inspired stretchable electronic skin (e-skin), in which the e-skin colour can easily be controlled through varying the applied pressure along with the applied pressure duration. As such, the e-skin's colour change can also be in turn utilized to distinguish the pressure applied. The integration of the stretchable, highly tunable resistive pressure sensor and the fully stretchable organic electrochromic device enables the demonstration of a stretchable electrochromically active e-skin with tactile-sensing control. This system will have wide range applications such as interactive wearable devices, artificial prosthetics and smart robots.

An investigation on the optical properties of regioregular Poly(3-Hexylthiophene)

Among semiconducting polymers, poly(3-alkylthiophene)s have attracted great attention and generated many studies over the past few years. Among them, regioregular (head-to-tail) poly(3-hexylthiophene) (P3HT) has been especially investigated due to its superior opto-electronic properties, good solubility in the most common organic solvents, chemical and thermal stabilities and also very low toxicity. These properties enable P3HT to be significantly useful in a large variety of applications such as optical sensors, smart windows, organic field effect transistors (OFETs), electrochromic devices, and solar cells. Here, we report the synthesis of poly(3-hexylthiophene) (P3HT) and investigate the optical properties of P3HT in different solvents such as chloroform, tetrahydrofuran, toluene, ethylacetate. The structures of P3HT were confirmed by nuclear magnetic resonance (1H NMR), gel permeation chromatography (GPC), Fourier transform infrared (FT-IR).

A review of organic electrochromic fabric devices

Electrochromic fabric devices represent a further extension to the plethora of available literature on conductive fabrics. This article contains a brief overview of electrochromic devices, electrochromic polymers, conductive materials, conductive fabrics, and electrochromic fabric devices. A tabulated list of the perceived colour of a number of electrochromic polymers that is contained herein is designed to serve as an aide to colour mixing studies. The challenges of optimisation and commercialisatiion of electrochromic fabric devices and their mitigating factors are conjectured, along with some future potential applications for electrochromic fabric device technologies.

A first truly all-solid state organic electrochromic device based on polymeric ionic liquids

Using polymeric ionic liquids and PEDOT as ion conducting separators and electrodes, respectively, an all-polymer-based organic electrochromic device (ECD) has been constructed. The advantages of such an ECD are: fast switching time (3 s), high coloration efficiency (390 cm(2) C(-1) at 620 nm), optical contrast up to ΔT = 22% and the possibility of working under vacuum.