Electrochromic Cell Research Articles

Structure-Dependent Response Characteristics of Electrochromic Dye-Modified Transparent Conductive Oxide Porous Electrode

Fast-response electrochromic (EC) cell composed of EC dye-modified TiO2-nanoparticle-based transparent porous electrode was reported by R. Cinnsealach et al. (Sol. Energy Mater. Sol. Cells, 55, 215, 1998). From then, TiO2 porous electrodes modified with EC dyes have been regarded as a promising candidate for fast-response EC display (ECD) applications. Our research purpose is the realization of flexible fast-response ECD applications. However, TiO2 porous electrodes require high sintering temperature (>400 °C) to use as EC electrode because TiO2 has high resistivity. This high process temperature required by TiO2 porous electrode was an important obstacle for their application as transparent electrodes in plastic substrate-based flexible ECDs. To solve this problem, we substituted transparent conductive oxides (TCO) for TiO2 as the porous electrode material. TCO materials have high electrical conductivity than TiO2, so they have the potential to work as the EC electrode even if they are sintered at low temperature. Previously, we reported that the porous electrodes consisting of indium tin oxide (ITO) nanoparticles exhibit good optical transparency and high electric conductivity. Moreover, EC response characteristics of EC-dye modified ITO porous electrode sintered at 150 °C was improved than that of conventional TiO2 porous electrode due to its high conductivity (AIP Adv., 6, 065121, 2016). Therefore, TCO porous electrodes have potential for application in porous electrode for flexible ultrafast-response ECDs. To achieve such applications, it is necessary to analyze the factors controlling the EC response speed in TCO porous electrodes. In this study, we investigated the response characteristics of EC dye-modified ITO, antimony-doped tin oxide (ATO), and TiO2 porous electrodes. ITO and ATO porous films have low electric resistivity due to their high electric conductivity. As mentioned above, ITO porous electrode exhibited fast response. On the other hand, low-resistivity ATO porous electrode exhibited slower response than that of a conventional high-resistivity TiO2 porous electrode. This clearly indicates that the EC response speed of the ATO porous electrode is dependent on a factor other than the electric resistance of the porous film. From the structural comparisons, it is revealed that the pore size of the film consisting of small nanoparticles is one of the key factors controlling the EC response speed of porous electrode. The details about the effect of porous film structure on EC response characteristics will be discussed.

Electrochromic properties of thin nanocrystalline TiO2 films coated electrodes with adsorbed Co(II) or Fe(II) 2,2′-bipyridine complexes

A novel method of preparation of electrochromic cells with a cobalt(II) or iron(II)-tris-2,2′-bipyridine hexafluorophosphate dye adsorbed on a titanium dioxide coated electrode and platinum or nickel oxide thin coated counter-electrode in conjunction with quasi-solid state LiClO4 based electrolyte is presented. The operation of the cells was analyzed using cyclic voltammetry as well as by UV–vis reflectance and transmittance spectroscopy. The transition times between the tinted and bleached states are of the order of one second, while the difference between both states is clearly visible. Best characteristics were obtained with the cobalt bipyridine hexafluorophosphate complex dye adsorbed on a mesoporous TiO2 electrode in combination with NiO counter-electrode. Devices created according to the described method could potentially be used to recycle and re-use exhausted dye-sensitized solar cells for transparent smart windows, or as a new type of displays.

Development of photochromic device with magnetron sputtered titanium dioxide and tungsten trioxide films

A photochromic (PC) device comprising an electrochromic film (WO3) together with a photoactive film (usually, dye sensitized TiO2) coated on glass and a redox electrolyte (e.g., iodide/triiodide together with lithium salt) reduces the optical transmission under solar illumination and bleaches, again, in dark or at low intensity of light. This work reports, for first time, on an application of sputter coated TiO2 and WO3 films for this type of PC devices. The applicability of TiO2 and WO3 films in PC device is individually investigated in dye solar cells and electrochromic cells, respectively. A dye solar cell with 180nm TiO2 was shown to be sufficient for the charge generation for electrochromic coloration of the WO3. The compatibility of WO3 and redox electrolyte was studied in electrochromic devices by considering their redox potentials. The bleaching of the PC device has to be adjusted by the so called “loss current”. To address this, a thin catalytic layer of platinum (Pt) is deposited in between the photoactive and electrochromic layers. The optimized PC device exhibits a visual (solar) transmission modulation from 74 (63) down to 30% (20%) in 40min under 1.5 A.M. illumination, and the bleaching is regained in 45min in dark.

Photoelectrochromic devices based on sputtered WO3 and TiO2 films

The photoelectrochromic (PEC) device, a combination of a dye solar cell and an electrochromic film, can be used for the dynamic solar control of buildings under illumination or with an external voltage. Typically, titanium oxide (TiO2) and tungsten oxide (WO3) films are being prepared from colloids or sol-gel chemistry with high porosity and high surface area as functional layers for a photoelectrochromic device in lab scale. We have, for the first time, successfully developed a PEC device with conventionally sputter deposited TiO2 and WO3 films. This coating technique is attractive due to the well documented upscaling capability and industrial viability for window applications. The functional layers WO3 and TiO2 were deposited onto fluorine doped oxide (F:SnO2) coated glass . Characterization of WO3 and TiO2 was performed in an electrochromic cell and in a dye solar cell, respectively. Three types of PEC devices with different layer configuration were constructed and their performance based on visual transmissions was compared. In best case, the visual transmission could be switched from 61 down to 15% in 30min under 1.5 A.M. illumination.

Benzodithiophene and Benzotriazole Bearing Conjugated Polymers for Electrochromic and Organic Solar Cell Applications

Herein, alternating donor-acceptor type benzodithiophene and benzotriazole bearing copolymers were synthesized and thieno[3,2-b]thiophene and furan units were incorporated as π-bridges. The application of these polymers for electrochromic and photovoltaic studies were performed. Spectroelectrochemical studies illustrate that both polymers showed multichromic behavior due to tailoring of polaron bands in visible region. Photovoltaic properties of P2 were performed by conventional device structure. The best performance device based on P2: PC71BM (1:3, w/w) exhibited the power conversion efficiency of 2.98%, with Voc of 0.74 V, Jsc of 6.31 mA/cm2, and FF of 64%. The carrier mobility of the P2: PC71BM was calculated as 1.37 × 10−3 cm2/V.s via space-charge-limited current method.

A Fluorescence and Electroactive Surface Design: Electropolymerization of Dansyl Fluorophore Functionalized PEDOT

Fluorescent conducting polymers are gaining increasing popularity in actual applications such as electrochromic device, cell detection and fluorescence sensor. This paper describes the synthesis of new both fluorescent and electrochromic polymer. A new bifunctional material 2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)methyl 5-(dimethylamino)naphthalene-1-sulfonate (ED) has been synthesized, characterized and electropolimerized. The polymer film which obtained as a highly stable conducting polymer on ITO glass was characterized by cyclic voltammetry (CV), colorimetry, UV–Vis spectroscopy, fluorescence spectroscopy, fluorescence microscopy and scanning electron microscopy (SEM). The PED film demonstrated light blue, gray and purplish blue colors as well as turquoise blue fluorescence color. Both CV and spectroelectrochemical studies proved that the PED film has exhibited high stable electro activity (98%). Further kinetic studies presented that the PED revealed high optic contrast (36%) and relatively low electrochromic response time (2.0 s). The results prevailed that the PED film is promising candidates for fluorescent detection and device applications.

Electrochromic thin-film components for information representation systems

The solutions in the sphere of energy efficient technologies of information representation systems development are overviewed in this paper. The main emphasis is on “electrochromism” phenomenon, which is a reversible change of material optical characteristics during the application of an external electrical potential. The possible use of electrochromism phenomenon in energy-efficient electromagnetic radiation modulation systems is shown. The generalized model of the universal electrochromic cell construction is presented. The materials with electrochromic characteristics, the field of electrochromes use and the developments in the sphere of electrochromic technologies are analyzed.

Thickness dependence of electro‐optical properties of WO3 films as an electrochromic functional material for energy‐efficient applications

WO3 films of different thicknesses (100, 200, and 300 nm) were prepared by two vacuum physical vapor deposition (PVD) methods (thermal evaporation and an electron gun). Electrophysical measurements (cyclic voltammetry and chronoamperometry) were carried out using a potentiostat in an electrochromic cell (liquid device) that consists of a substrate coated with double layers of F: SnO2 and WO3 served as working electrodes. X‐ray diffraction showed an amorphous structure for all the deposited WO3 thin films. While the transmission in the bleached state does not change and it is close to the as‐deposited state, it is slightly less at larger thickness. The cyclic voltammogram was more open (more current flow) for thicker films due to the less dense structure with many channels. Also, the coloration efficiency was higher at low thickness. The response time was of the order of seconds and decreased for coloration, while it increased for the bleaching process as the film thickness increases. According to the proposed figure of merit, the electrochromic performance deteriorates as the WO3 film thickness decreases. However, the thickness is more effective in the case of an electron gun. Generally, continuous films but thinner than 200 nm, are recommended for deposition methods.

Photoelectrochromic devices: Influence of device architecture and electrolyte composition

Solar energy harvesting and chromogenic technologies can be integrated together to give self-powered and wireless photoelectrochromic devices (PECD). Due to the similarity in the architecture of both dye-sensitized solar cells (DSC) and electrochromic devices (ECD), it is possible to merge these two devices into one combined solar-powered electrochromic device known as DSC-EC. The present work describes the preparation and characterization of electrochromic solar cells using PEDOT:PSS (poly(3,4-ethylenedioxythiophene) polystyrene sulfonate) as electrochromic material in the counter-electrode. Different configurations and liquid and polymer-based electrolytes are studied. The resulting electrochromic solar cells were characterized focusing on the determination of solar to electricity conversion efficiency and the color contrast was assessed using color coordinates under simulated solar irradiation. The best DSC-EC configuration originates a color contrast of (ΔE=30) at a potential difference of 0.4V and energy conversion efficiency of 4.9% at VOC of 0.66V and JSC of 11 mAcm−2, when using the liquid electrolyte. On the other hand, the best performing DSC-EC using the polymer-based electrolyte showed a very good color contrast of (ΔE=47) at short circuit and an energy conversion efficiency of 1% at VOC of 0.63V and JSC of 4.5 mAcm−2.

Using WO3 as a transparent, optically-passive counter electrode in an unbalanced electrochromic configuration

Electrochromic cells in a proposed new architecture, called unbalanced configuration, were constructed using poly(2,2-dimethyl-3,4 propylenedioxythiophene) (PolyPRODOT-Me2) as the working electrode and tungsten trioxide (WO3) as the counter electrode. This unbalanced system allowed us to drastically change the electrochromic behavior of WO3, using it as an optically-passive transparent material, therefore confirming the potential of this new configuration as a viable alternative in the design of electrochromic devices. Functional electrochromic cells working under a narrow voltage of 1.5V and reaching an optical contrast of 52% at 566nm were constructed and tested.

Effect of substituent groups on quinoxaline-based random copolymers on the optoelectronic and photovoltaic properties

Abstract In this study, three low band gap donor-acceptor (D-A) type quinoxaline-based random copolymers were synthesized. The effect of varying substituent groups on quinoxaline groups on optoelectronic properties and the performance of bulk-heterojunction polymer solar cells was investigated. Electrochemical and optical studies indicate that these copolymers are promising materials for both electrochromic and polymer solar cells applications. Two random polymers were found as excellent candidates for NIR electrochromic devices owing to their 60% and 94% optical contrast values respectively in NIR region with less than 1 s switching times. Polymer solar cells were constructed using the copolymers as the donor components together with PC71BM as the acceptor in the active layer. Among all, the highest PCE was reported as 2.13%.

High Frequency Dielectric Characteristics of Electrochromic, WO3 and NiO Films with LiNbO3 Electrolyte.

A great deal of attention has been recently focused on Electrochromic (EC) materials and EC based devices, promoting mainly applications related to display technology. In this case, EC based displays are usually actuated by the application of low dc bias voltages, changing their appearance from transparent to opaque. A variety of studies related to the optical characteristics of EC materials have been reported, however, no serious studies so far have been reported on the possible high frequency tunability of the dielectric characteristics of these materials, with the exception of the work by Rose, which presented the operation of a microwave shutter based on conductive polymers operating in the X-band. Here we report tuneable high frequency dielectric characteristics of an Electrochromic (EC) cell with a complimentary structure of Conductor/WO3/LiNbO3/NiO/Conductor in the frequency range from 1 GHz to 20 GHz. The EC cell was prepared using standard semiconductor processing technology, such as lithography, etch and deposition techniques. Our measured results indicate that tunability of high frequency dielectric characteristics as a function of dc bias voltage is achieved, and that a possibility exists for this tunability to be tailored.

Crosslinked Gel Polymer Electrolytes with Different Li Salts for Electrochromic Cells

The use of electrochromic windows to control heating and cooling loads in buildings and automobiles have attracted a lot of attention as a new and emerging strategy towards energy saving and energy storage to combat global warming and the energy crisis. The types of electrolyte salts employed in an electrochromic device is of great significance to the charge transfer which are in the form of ions between the electrodes. Thus, the electrolyte salt must be viewed as inert component of the electrochromic cell and it should be stable towards the cathode and anode. Hence, we conducted a comprehensive studies based on experiments on the effects of different salts in gel polymer electrolytes on the performance of electrochromic cells consisting of WO3/ITO as the working electrode and NiO/ITO as the counter electrode. Three different salts, 1M LiClO4, 1M LiFSI and 1M LiTFSI in propylene carbonate(PC)/polyethylene glycol diacrylate (PEGDA, Mn: 575) (7/3, v/v) were used in this study. Their ionic conductivities as well as the color changing behavior in the electrochromic cell were investigated. Acknowledgements This work was supported by the *Energy Technology Program of the Korea Institute of Energy Technology Evaluation and Planning(KETEP) granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20142010102980) Figure 1

A greener electrochromic liquid crystal based on ionic liquid electrolytes

ABSTRACTAn electrochromic liquid crystal (ECLC) material composed of only liquid crystal (LC) and ionic liquid (IL) was developed. The LC containing the substituted diphenylacetylene serves as electrochromic (EC) material to realise transmittance and colour change under the direct current (DC) field, while the IL with the designable cation and anion served as electrolyte. Herein, a series of IL electrolytes was screened to investigate how IL tunes the electro-optic performance of the ECLC cell. By testing the electrochemistry window of ILs in EC cells, IL with the [NTf2]− anion shows adequate electrochemical stability when the EC material undergoes oxidation and reduction. The electro-optic performance of ECLC containing 1-ethoxy-4-[2-(4-pentylphenyl) ethynyl]-benzene (PEB) and IL was then evaluated by UV-vis spectrometry under the control of an electrochemical work station. Compared with other PEB-IL, PEB-[Bmim][NTf2] with [Bmim][NTf2] electrolyte shows a satisfactory transmittance at low operating voltage. Furthermore, Pd NPs in situ formed in [Bmim][NTf2] reduced the EC potential and improved the light scattering of the ECLC cell. In this work, we also designed a bifunctional device based on polymer dispersed liquid crystal (PDLC) that hosts electrochromic guest molecules, and analysed the electro-optical and electrochromic properties of LC electrolyte mixtures, in order to gain control of the incident daylight and glare in building and automotive applications.

Synthesis and characterization of triphenylamine-based polymers and their application towards solid-state electrochromic cells

Triphenyl amine based new molecules have synthesized for electrochromic cells. We achieved color change forPJK1, orange to dark green; forPJK2, light yellow to reddish brown; forPJK3, light blue to grey; and forPJK4, green to bluish green.

Organophosphorus derivatives for electronic devices

This review presents the main class of organophosphorus compounds (triaryl phosphines, phosphazenes, phospholes, phosphetes and diphosphacyclobutanes), which have been used in electronic devices (organic light-emitting diodes (OLEDs), organic photovoltaic cells (OPV cells), dye-sensitized solar cells (DSSCs), organic field-effect transistors (OFETs), and electrochromic cells).

PV 일체형 차세대 스마트 윈도우 기술개발 동향

Among several types of energy saving smart window technologies, the leader, the dynamic EC (electrochromic) window one needs integrated PV (photovoltaics), to minimize expensive electrical wiring as well as to obviate the need for external energy. Self-powered smart windows were reviewed according to PV types used. DSSCs (dye sensitized solar cells) were found to be compatible with EC cells, to have several categories of next generation smart windows such as PECCs (photoelectrochromic cells), PVCCs (photovoltachromic cells), EC polymer PECCs. In addition silicon solar cells and third generation solar cells were investigated. They are summarized in a table showing their advantages and disadvantages respectively for a fast comparison. The strategy to expedite the commercialization of these next generation smart windows includes developing retrofit smart window coverings for use on flexible polymer substrates adhered to the inside surface of a window and easily replaced after use for upto 10 years.

Properties of Electrochromic Cell with WO3 and NiO: the Influence of Ionic Conductor

The electrochromic WO3 and NiO films were deposited by magnetron sputtering on indium tin oxides coated glass. The structural properties of the films were investigated by scanning electron microscopy and X-ray diffractometery techniques. The electrochromic properties of the films were investigated by means cyclic voltammetry using different types of ionic conductors. The use of water electrolytes and electrolytes which are based on propylene carbonate leads to the destruction of electrochromic cells. The stable working electrochromic cell with WO3 and NiO films was obtained using ionic liquid as the ionic conductor. The coloration efficiency of electrochromic cell which is based on amorphous WO3 film and crystalline NiO film is 28.7 cm2/C.

Chromatic control of multicolor electrochromic device with localized surface plasmon resonance of silver nanoparticles by voltage-step method

Inorganic electrochromic (EC) materials are of interest because of their many possible applications, including use in information displays. The multifunctional EC materials that enable control of multiple colors and color depth have considerable promise as candidates for full color EC display devices. In this research, we focused on Ag nanoparticles that exhibit various colors on the basis of their localized surface plasmon resonance (LSPR). Because the LSPR band depends on the size and shape of the nanoparticles, control of the morphology of Ag nanoparticles can lead to dramatic changes in color. In order to apply this color variation for display devices, we utilized here the electrochemical formation of size-controlled Ag nanoparticles using a voltage-step method that consists of an application of two successive different voltages. In order to improve the variation of colors of the EC cell, the effect of application voltages and their times on morphology of deposited silver were investigated. The relationship between the morphology of the deposited Ag nanoparticles and color of the EC cell was discussed, and then we successfully represented multiple coloration of the EC cell with various color depth.

Electrochromic thin films of sodium intercalated vanadium(V) oxide xerogels: Chemical bath deposition and characterization

An optimized chemical bath method is applied to obtain well-structured thin films with composition Na0.33V2O5·nH2O (n=1 and 1.3). The method is based on a controlled precipitation reaction that takes place in the system of sodium metavanadate and diethyl sulfate at 85°C. The film structure, morphology and the changes occurring during prolonged aging are examined by XRD, IR spectroscopy, TG-DTA, SEM and AFM. The electrochemical and electrochromic properties are studied by cyclic voltammetry and UV–vis spectroscopy. The as-deposited thin films are characterized with high optical transmittance varying between 40 and 70% at the 500nm visible region in dependence on film thickness. The Na0.33V2O5·nH2O thin films exhibit stable electrochemical cycling combined with relatively high electrochromic activity. The reproducibility of the transmittance variance of 55% after 500cycles in the electrochromic cell is a promising result for the potential application of Na0.33V2O5·nH2O thin films in electrochromic devices.