Organic Electrochromic Materials Research Articles

Graphene Oxide Layers for a Long-Term Stable Electrochromism

In general, organic electrochromic materials have shown a poor long-term stability during the electrochemical reactions, which is mainly due to the weak mechanical properties of the mateials in orgnanic electrolytes. There have been several approaches to enhance the stability of electrochromic polymers. As one of the effective methods, incorporation of graphene oxide (GO) into the polymers has been introduced to solve the stability issue because GO has known to significantly improve the physical properties of polymers having a good compatibility with them. A poly(3-hexyl thiophene) (P3HT) is one of the important electrochromic polymers showing color changes between red and pale blue during electrochemical reactions. However, a poor life time of P3HT is deemed a main obstacle to utilize it as an aictive layer in commercial applications such as displays or smart windows. In this study, we prepare the electrochromic P3HT layer modified with GO and discuss the electrochromic properties of the composites. In order to construct the composites, the GO protective layer which has been modified by octadecylamine (ODA) is transferred on spin-coated P3HT layer by using Langmuir-Schaefer technique. The GO-ODA protective layer shows a high coverage with closed packed molecules and a good compatibility with P3HT layer. Furthermore, it is observed that the P3HT modified by GO-ODA protective layer shows a superior long-term stability compared to pristine P3HT layer during electrochromic reactions.

A Redox-Dependent Electrochromic Material: Tetri-EDOT Substituted Thieno[3,2-b]thiophene.

Organic electrochromic materials change color rapidly under applied potential. A butterfly-shaped compound, 5,5',-5″,-5'″-(thieno[3,2-b]thiophene-2,3,5,6-tetrayl) tetrakis-(2,3-dihydrothieno[3,4-b][1,4]dioxine) (t-EDOT-TT) is synthesized for the first time and polymerized at different potentials via electropolymerization technique. By applying different polymerization potentials, the optical and electrochromic properties of this newly synthesized polymer can be tuned. Owing to the dependence of functional group position in the polymer structure on the redox potential, this polymer can be utilized in very interesting organic optoelectronic applications.

Synthesis and electrochromic properties of star-shaped conjugated oligomers

To develop novel organic electrochromic materials, the star-shaped conjugated oligomers 1,3,5-tri[5′,2″-(3″,4″-ethylenedioxythineyl)-2′-thienyl]-4-(3′,4′-ethylenedioxythineyl) benzene (3TB-4EDOT) and 2,4,6-tri(2′-thienyl)-1,3,5-triazine (3TT) are synthesized. Two electrochromic devices are fabricated using 3TB-4EDOT or 3TT as an electrochromic active layer, and the device structures are indium tin oxide (ITO)/3TB-4EDOT (or 3TT)/electrolyte solution/Pt and ITO/3TB- 4EDOT (or 3TT)/conducting gel/ITO. The electrochromic properties of 3TB-4EDOT and 3TT are studied. 1,3,5-tri[5′,2″-(3″,4″-ethylenedioxythineyl)-2′-thienyl]-4-(3′,4′-ethylenedioxythineyl) benzene and 3TT as solid films show reversible, clear colour changes upon electrochemical doping and dedoping.

A single-molecule multicolor electrochromic device generated through medium engineering

Multicolor organic electrochromic materials are important for the generation of full-color devices. However, achieving multiple colors using a single-molecule material has proved challenging. In this study, a multicolor electrochromic prototype device is generated by integrating medium engineering/in situ ‘electro base’/laminated electrode technologies with the simple flying fish-shaped methyl ketone TM1. This multicolor electrochromic (green, blue and magenta) device is durable and has a high coloration efficiency (350 cm2 C−1), a fast switching time (50 ms) and superior reversibility. This study is a successful attempt to integrate solvatochromism and basochromism in an electronic display. This integration not only introduces a new avenue for color tuning, in addition to the structural design of the colorant, but will also inspire further developments in the tuning of many other properties by this medium engineering approach, such as conductance and the redox property, and thereby accelerate versatile applications in data recording, ultrathin flexible displays, and optical communication and sensing. Using medium engineering, researchers in China have made a multicolour electrochromic device that employs a single organic compound. Organic electrochromic materials appear promising for meeting the high demand for low-power, ultrathin, flexible electronic displays but have so far been incapable of producing the three primary colours needed. Now, Yu-Mo Zhang and co-workers at Jilian University have produced a multicolour electrochromic device based on a single small-molecule organic compound, methyl ketone. They tuned the colour by varying the ratio of the two plasticizers used, allowing them to produce three primary colours. Their device has a fast switching time (50 ms), a large colouration efficiency (350 cm2 C–1) and a good reversibility. This medium-engineering approach has the potential to tune other properties and spawn applications in optical communication and sensing, data recording and ultrathin flexible displays.

Multichromophoric electrochromic polymers: colour tuning of conjugated polymers through the side chain functionalization approach

Organic electrochromic materials have gained constantly increasing interest over the years with respect to their inorganic counterpart due to essentially two distinctive characteristics: their processability through solution based low cost processes and their wide colour palette. Such characteristic features enabled their application in displays, smart windows, electronic paper and ophthalmic lenses. Alongside the established concept of donor-acceptor polymers, side chain functionalized multichromophoric polymers are gaining attention as a highly performing and synthetically feasible alternative, particularly relevant to applications requiring a complete colourlessness in one of the accessible redox states of the material. The primary aim of the present article is to review all the results involving the tuning of the native electrochromic properties of simple conjugated polymers through the introduction of a discrete electrochromic molecule as a side chain substituent.

Organic Electrochromic Materials: A Brief Review of Viologens, Phthalocyanines and Some Complexes of Transition Metals

Organic Electrochromic Materials: A Brief Review of Viologens, Phthalocyanines and Some Complexes of Transition Metals

Organic Electrochromic Materials and Device toward Color Electronic Paper

We prepared solid-state electrochromic (EC) cells based on phthalate derivatives and containing a gel electrolyte. The cells showed vivid color changes via electrochemical reactions, i.e., from being water transparent to assuming one of the three primary colors (cyan, magenta, and yellow). Moreover, we obtained continuous-tone images by using the three primary-color EC cells. The formation of continuous-tone images by using the EC cells was realized by applying a rectangular-wave voltage with various duty ratios. In addition, according to a subtractive color-mixture process, we obtained multiple color representations, including intermediate red, green, and blue colors, by stacking two of the three primary-color EC cells.

Synthesis and electrochromic properties of oligothiophene derivatives

In order to develop novel organic electrochromic materials, oligothiophene derivatives, 5,5″-biformyl-2,2′:5′,2″-terthiophene (OHC-3T-CHO) and 2,3,4,5-tetrathiopenyl-thiophene (X-T), were synthesized. Three electrochromic devices have been fabricated using OHC-3T-CHO and XT, and the electrochromic properties of OHC-3T-CHO and X-T were studied. The indium-tin-oxide (ITO)/OHC-3T-CHO/electrolyte solution/ITO device exhibited reversible, clear colour change from yellow to bright bluish-green on electrochemical doping and dedoping, while ITO/OHC-3T-CHO/conducting gel/ITO device and ITO/OHC-3T-CHO/conducting filter paper/ITO device exhibited colour change from yellow to green. The ITO/XT/electrolyte solution/ITO device showed reversible, clear colour change between yellowish orange and silver-gray on electrochemical doping and dedoping.

Multi-Color Electrochromic Device Based on Organic Electrochromic Materials

Multi-color electrochromic (EC) device was fabricated on a patterned ITO glass. Organic electrochromic dyes were encapsulated within nano-sized porous TiO2 nanoparticles, and their relative electrochromic (EC) properties were determined using spectroelectrochemical method. Blue, green, and red colored organic dye doped TiO2 nanoparticles were coated on a patterned ITO substrate to afford multi-colored EC electrode, which was coated with a photo-curable polymer electrolyte and then covered with a bare ITO glass as a counter electrode. Upon photocuring of the electrolyte layer under UV light, an all-solid state multi-colored electrochromic device (ECD) was obtained. The resultant ECD showed reversible multi-color change within 8 sec and high optical contrast.

5-Substituted isophthalate-based organic electrochromic materials

A new series of isophthalate-based electrochromic materials were prepared. The functional groups at the 5-position of isophthalate have a significant influence on the observed color. In particular, an electrochemically active nitro group induced a multi-color display, indicating that further electrochromic properties could be manipulated using more diverse 5-substituted isophthalate derivatives.

Organic Polymeric Electrochromic Devices: Polychromism with Very High Coloration Efficiency

The electrochromic properties of electrodeposited poly(1,4-bis(2-[3‘,4‘-ethylenedioxy]thienyl)-2-methoxy-5-2‘ ‘-ethylhexyloxybenzene) (P(BEDOT-MEHB)), a material for polymer electrochromic displays, are reported in detail. While the polymer is transparent in the fully oxidized state, two absorption bands obtained in the visible region for the neutral and partially oxidized polymer are due to two different colors from the same material. Compared to other inorganic or organic electrochromic materials, the P(BEDOT-MEHB) films exhibited very high coloration efficiency values: as high as 680 cm2/C at 535 nm and −360 cm2/C at 760 nm. The films have the advantage of exhibiting cathodic and anodic coloration. The space created by the methoxy ethylhexyloxy benzene between EDOT units on the polymer backbone makes the injection/rejection of the negatively charged counterions inside/outside of the polymer easier, resulting in higher doping levels than PEDOT at the same optical density. Very well-defined electrochemistry, high level of stability to overoxidation and long-term switching, and the chromicity properties mentioned above make P(BEDOT-MEHB) an excellent candidate for electrochromic displays.

Study of the potassium ion insertion of the electrodeposited electrochromic tungsten trioxide thin films

Various types of dynamic adjustable optical shutters have been proposed; they are called as “smart windows”. The electrochromic smart window utilizes the phenomenon of electrochromism. Electrochromism is the property of a material such that its color is changed by an electrochemical redox reaction. Numerous inorganic and organic electrochromic materials have been examined. During the color-bleach process, the redox reaction of the host material causes injection or ejection of both cation (or anion) and an electron (or hole). So it behaves as a mixed ion conductor and hence it has recently attracted interest in the field of solid state ionics. At present, several prototypes of electrochromic smart windows have been proposed and some of them are commercially available. The cathodic electrochromic oxides consist of n-type semiconductors such as TiO2, V2O5, WO3 and MoO3. Among them, WO3 has been intensively examined and used for most electrochromic devices. These materials are cathodically colored in blue. The electrochromic reaction is expressed by $$xA^ + + MO_y \left( {transparent} \right) + x e^ - \Leftrightarrow A_x MO_y \left( {blue} \right)\left( {A = H, Li, Na, K \ldots , MO_y = metal oxide} \right)$$ where the cation A+ and electron e− are co-injected into the host oxide MOy which results in the formation of the nonstiochiometric compound AxMOy. Here the electrodeposition method is used to deposite WO3 films under by galvanostatic conditions. The parameters like deposition time, deposition temperature, electrolyte concentration, pH and bath temperature are optimized. The XRD results show the triclinic structure for the as-deposited film. The film shows the same structure after intercalation but the peak intensity is different. The tungsten trioxide thin films show the colour change during the intercalation and retrace the original colour. The diffusion coefficient for K+ ion is calculated by using the Randles-Servick equation. In this paper the electrochromic properties, the optical properties of the as deposited, ion intercalated and deintercalated WO3 films and the diffusion coefficient values are presented.

Current state of the art for NOC-AGC electrochromic windows for architectural and automotive applications

We have designed and synthesized a large number of donor–acceptor type organic electrochromic (EC) materials to increase the resistance to ultraviolet irradiation. The guiding principle for the molecular design is given briefly. One of the materials is a viologen-ferrocene EC material. In this paper, we report two different types of electrochromic windows (ECWs): one is fabricated with a viologen-ferrocene EC material, and the other with a carbon-based electrode. The coloration process of the viologen-based ECW is also discussed with reference to the driving voltage dependence. Outdoor weathering tests were carried out on ECWs designed for automotive applications. The 2-year outdoor weathering tests suggest a potentially high durability.

Electrochromic Behavior of Ionically Self-Assembled Thin Films

ABSTRACTIonically self-assembled monolayers (ISAMs), fabricated by alternate adsorption of cationic and anionic components, yield exceptionally homogeneous thin films with sub- nanometer control of the thickness and relative spatial location of the component materials. Using organic electrochromic materials such as polyaniline, we report studies of electrochromic responses in ISAM films. Reversible changes in the absorption spectrum are observed with the application of voltages on the order of 1.0 V. Measurements are made using both liquid electrolytes and in all-solid state devices incorporating solid polyelectrolytes such as poly(2- acylamido 2-methyl propane sulfonic acid) (PAMPS).

Organic electrochromic materials

In this article some of the most important examples from the major classes of organic electrochromic materials, namely the 1,1′-disubstituted-4,4′-bipyridilium salts (the `viologens'), conducting polymers, metallopolymers and metallophthalocyanines are reviewed. Examples of their use in both a commercial and several prototype electrochromic devices are given.

Recent trend in thin film formation for electrochromic display materials.

Elctrochromic materials and thin film formation techniques are reviewed. Transition metal oxides, such as WO3, MoO3, NiOOH, and IrOx are chemically or electrochemically filmed on ITO glasses. These methods can be used for the large scale production of the desplay surface.In the case of organic materials, viologens are the most comonly used. During repeated coloration and bleaching, these materials are, however, easily converted into irreversible species. This is stabilized by clusrate formation with cyclodextrin.Anodic polymerization of aniline or pyrole is of alternate possibillity of the organic electrochromic materials. Since the ECD is one of the electrochemical cells, the two electrodes and electrolyte between them are the basic components. Therefore, the selection of the electrolyte is of great importance, as well as the selection of the elctrochromic materials.Finally the merit and demerit of the ECD are described.

Electrochromic materials and devices for energy efficient windows

Numerous inorganic and organic electrochromic materials are discussed in the context of developing a film-based optical shutter for a window application. It is possible electronically to alter a window's transmission and reflection properties by use of electrochromic thin films. This allows regulation of conductive and radiative heat transfer rates, with variable optical attenuation. As a result, an aperture can be optically and thermally managed, reducing space heating and cooling loads. The properties of transition metal oxides, such as WO 3, MoO 3, Ir 2O 3 and V 2O 5 are detailed. Organic systems such as heptyl viologen and polytungsten anion are reviewed. Also, intercalated structures are discussed. Various designs of working devices are outlined with emphasis on solid-state configurations. From this quantification, materials and devices with appropriate deposition techniques for window applications are detailed.