Use In Electrochromic Devices Research Articles

A stimuli-responsive viologen-containing polymer for use in electrochromic devices and amine-detecting paper

The synthesized viologen-containing polyurethane exhibits excellent electrochromic performance and high sensitivity to amine compounds. This dual functionality makes it a candidate for use in electrochromic devices and amine detection sensors.

Iron (II) Metallo-Supramolecular Polymers Based on Thieno[3,2-b]thiophene for Electrochromic Applications.

Four new bis(tpy) unimers with different linkers between the thieno[3,2-b]thiophene-2,5-diyl central unit and terpyridine-4′-yl (tpy) end-groups: no linker (Tt), ethynediyl (TtE), 1,4-phenylene (TtPh) and 2,2′-bithophene-5,5′-diyl (TtB) are prepared, characterized, and assembled with Fe2+ ions to metallo-supramolecular polymers (Fe-MSPs). The Fe-MSP films prepared by spin-casting on Indium Tin Oxide (ITO) glass are characterized by atomic force microscope (AFM) microscopy, cyclic voltammetry, and UV/vis spectroscopy and studied for their electrochromism and effect of the unimer structure on their electrochromic performance. Of the studied MSPs, Fe-Tt shows the highest optical contrast as well as coloration efficiency (CE = 641 cm2 C−1) and the fastest optical response. This makes it an excellent candidate for possible use in electrochromic devices.

Investigating the structural, electrochemical, and optical properties of p-type spherical nickel oxide (NiO) nanoparticles

A facile and efficient co-precipitation method has been used to synthesize pure nickel oxide (NiO) nanoparticles. The synthesis of NiO has been conducted at two different pH values (11.00, 12.33) and in alkaline media of LiOH and NaOH, and the variations in structural, electrochemical, and optical properties have been analyzed. The particle sizes of all of the synthesized samples were in the range 8.000–20.00 nm, and their energy band gaps were in the range 3.500–4.000 eV. Williamson–Hall plots indicate that strain was introduced in the samples during the synthesis process. NiO nanoparticles synthesized in the LiOH medium at pH 12.33 showed the smallest crystallite size of 8.830 nm, with a lower strain value of 9.620E-6. The charge-transport and charge-transfer properties of the NiO samples have been investigated by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. CV study revealed that the redox process is diffusion-controlled, with a diffusion constant of the order of 10−10 cm2 s−1. Nyquist plots obtained by the EIS technique indicate how charge-transfer resistance and Warburg diffusion vary with pH. The NiO nanoparticles synthesized in LiOH medium at pH 12.33 showed the lowest charge-transfer resistance, indicating high electrical conductivity. In the present study, NiO nanoparticles with small crystallite size and lower strain value has been obtained, which form a better thin film suitable for use as a hole-transporting layer in solar cells. Lower charge-transfer resistance facilitates better charge transport in the obtained NiO nanomaterial, facilitating use in electrochromic devices.

Study of ionically conducting nanocomposites for reflective electrochromic devices

New, nanocomposite, and ionically conducting membranes have been developed by using plasticized and crosslinked gelatin and clay (montmorillonite SCa-3) with concentration of 1–20 wt%. The samples were studied by FTIR, X-ray diffraction, UV-Vis (transmittance and reflectance), CW-EPR, HYSCORE, and ionic conductivity properties. The obtained results have revealed that the incorporation of clay has promoted changes in the physical properties of the samples. The transparency of theses membranes decreased, while the reflectance augmented with the rise of the clay content. The best ionic conductivity result of 3.49 × 10−4 S/cm2 at 25 °C was obtained for the sample with 15 wt% of clay. CW-EPR spectra of Gel-SCa-3-Na samples doped with Cu2+ ions showed that SCa-3-Na had no significant impact on the Cu2+ local coordination surroundings and HYSCORE spectra showed one and two proton signals depending on the sample. Finally, the samples were inserted in the electrochromic devices (ECDs) composed of glass/ITO/Prussian blue/gelatin-SCa-3/CeO2-TiO2/ITO/glass. The best results were registered with the ECD containing 15 wt% of clay, which changed its reflectance from 15 to 8% at 450 nm. Moreover, this ECD demonstrated to be completely reversible. The obtained results confirmed the impact of the clay on the ionic conductivity, transparency, and performance of the ECDs. In summary, the nanocomposite electrolytes seem to be very interesting materials, mainly because of their possible practical use in electrochromic devices.

Electrochemical, UV–Vis, and microscopical characteristics of sol–gel CeO2:V2O5 thin film

Cerium dioxide (CeO2) and cerium dioxide doped with vanadium pentoxide (CeO2:V2O5) were synthesized from sol–gel precursors and deposited by spin coating on a conductive glass substrate (FTO). The films with different concentration of dopant and number of deposited layers were studied throughout cyclic voltammetry (CV), chronoamperometry/chronocoulometry, atomic force microscopy (AFM), scanning electron microscopy (SEM), and UV–Vis spectroscopy. The best value of charge density of 18.9 mC cm−2 was obtained for CeO2 doped with 15 mol% of V2O5 film. The chemical diffusion coefficient of lithium ions into CeO2 was 1.73 × 10−12 and CeO2:V2O5 15 mol% 6.75 × 10−13 cm2 s−1. This film presented 79% of transparency in UV–Vis and 5% color change under ± 1.3 V of applied potentials. Structural analyses revealed its homogeneous surface and the root mean-squared roughness (RMS) value of 9.42 nm. Based on the obtained results, CeO2 doped with 15 mol% V2O5 film is a promising thin coating for the use in electrochromic devices as a passive counter-electrode.

Effects of the redox group of carbazole-EDOT derivatives on their electrochemical and spectroelectrochemical properties

Three novel monomers based on carbazole-3, 4-ethoxylenedioxythiophene and redox groups were synthesized and characterized. Their polymer films were obtained by electropolymerization. Cyclic voltammetry and spectroelectrochemistry of the polymer films showed that they possessed multi-electrochromic property. The presence of ferrocene and 2,2,6,6-tetramethyl-1-piperidinyloxy units not only changed the films’ colour but also improved their switching time due to their excellent electrochemical properties. Additionally, the polymer films also possessed a reasonable transmittance change, which made them promising candidates for use in electrochromic devices.

Methyl-viologen modified ZnO nanotubes for use in electrochromic devices

Efficiently changing optical properties (reflectance, transmittance, and absorbance) through reversible color changes of electrochromic (EC) materials is challenging and critical in achieving high-performance EC devices.

Increasing the electrical conductivity of electrochromic PEDOT:PSS films – A comparative study

The present work describes the preparation and characterization of PEDOT films (different commercial screen-printing grades) mixed with intrinsically conductive materials such as graphene, graphite, silver nanowires or AZO (antimony doped zinc oxide) deposited on plastic and paper substrates using screen-printing. The final objective was to develop a material that could be used both as electrochromic material and as electrode (electrically conductive) for use in electrochromic devices, avoiding the use of an extra layer of conductive material such as a TCO, allowing the use of different substrates, shapes or sizes, because of the limitations found in TCO deposition. The resulting films were characterized in terms of electrical and optical properties, as well as electrochemical stability. Techniques such as cyclic voltammetry, UV–visible spectroscopy, scanning electron microscopy and mechanical tests were also used. Electrochromic devices (ECDs) were assembled using these PEDOT based electrodes. The performances of the resulting devices (3 layer structures) were compared with that of conventional ones (5 layer structures) through the analysis of the device color contrast over time during continuous operation conditions using a cycling program.

Electrochromic properties of iridium oxide thin films prepared by reactive sputtering in O2 or H2O atmosphere

Iridium oxide is an electrochromic (EC) material, i.e., it shows reversible and persistent changes in optical properties. In this study, the authors investigated the effects of substrate temperature and sputtering gas on the structures and EC properties of iridium oxide thin films prepared by reactive radio-frequency magnetron sputtering. An Ir metal target was sputtered in an O2 or H2O atmosphere at substrate temperatures between −30 and 130 °C. The crystal structures and chemical bonding states of the films were examined using x-ray diffraction and Fourier-transform infrared (IR) spectroscopy, respectively, and their EC properties were studied in 0.5 M aqueous H2SO4 electrolyte solution. IrO2 films were deposited at 70 and 130 °C, and amorphous films were formed at 20 and −30 °C in both O2 and H2O atmospheres. IR absorption peaks from hydrogen-bonded OH groups were clearly observed for films deposited in an H2O atmosphere at substrate temperatures of −30 and 20 °C, which indicates that iridium oxyhydroxide or hydrated iridium oxide films were deposited. The amorphous iridium oxyhydroxide or hydrated iridium oxide films showed large variations in transmittance and high bleached-state transmittances, and they are considered to be suitable for use in EC devices.

Direct preparation of electroactive polymers on electrodes and their use in electrochromic devices

Thermal polymerization of electroactive thin films using an aminobisthiophene vinylene monomer was done directly on electrodes. The resulting films reversibly switched colors in the visible-to-NIR regions, contingent on the monomers used for polymerization. Working transmissive electrochromic devices were fabricated using the electrode immobilized electroactive polymers. The devices exhibited reversible color changes with a moderate 150 duty cycle.

The effect of precursor aging on the morphology and electrochromic performance of electrodeposited tungsten oxide films

Tungsten oxide films that have larger effective surface area or extensive grain boundaries tend to be more suitable for use in electrochromic devices. We propose in this paper a simple methodology for increasing the roughness and thus the effective surface area of WO 3 films. This method is based on the tendency of the peroxytungstate precursor to form large aggregates within its solution with time. To this aim, a systematic study of the precursor aging effect on the resulting WO 3 film properties was conducted. It was established that with increasing aging time of the precursor solution, more and larger aggregates are formed, which are then deposited on the film surface. The deposition of the aggregates causes the formation of large cracks on the film surface, thereby increasing its effective area. An optimum of the precursor aging time was found to be around 80 h. Films prepared with such an aged solution were found to have the highest Li + diffusion coefficient and voltammetrically intercalated charge density per unit film thickness. It was also observed that the coloration efficiency of films prepared using the aforementioned method was higher than that of equivalent electron-gun deposited films throughout the visible spectrum and especially in the near infrared. The enhanced properties of these films indicate their improved electrochromic performance, which is mainly due to their increased surface area.

Green as it Gets; Donor‐Acceptor type Polymers as the Key to Realization of RGB Based Polymer Display Devices

AbstractSummary: Polymers that have one of the three complementary colors (red, green, and blue, RGB) in the neutral state and high transmissivity in the oxidized state are the key materials towards use in electrochromic devices and displays. Although many neutral state red and blue polymers have been reported up to date, green polymers with highly transmissive oxidized states, high optical contrasts, fast switching times, and advanced long‐term switching stabilities were essentially missing in the literature. This paper reviews our previous efforts towards realization of neutral state green polymers with highly transmissive oxidized state. The key to this problem was found to be the synthesis of donor‐acceptor polymers bearing benzothiadiazole or quinoxaline derivatives as the acceptor and electron rich 3,4‐ethylenedioxythiophene unit as the donor component. Green neutral state polymeric materials with highly transmissive oxidized state with excellent electrochromic properties have been realized with the design and synthesis of these types of materials. A solution processable green polymeric material has also been realized via chemical polymerization that has shown all superior properties of the electrochemically synthesized counterparts.

Self-assembled films from WO 3: Electrochromism and lithium ion diffusion

WO 3/chitosan and WO 3/chitosan/poly(ethylene oxide) (PEO) films were prepared by the layer-by-layer method. The presence of chitosan enabled PEO to be carried into the self-assembled structure, contributing to an increase in the Li + diffusion rate. On the basis of the galvanostatic intermittent titration technique (GITT) and the quadratic logistic equation (QLE), a spectroelectrochemical method was used for determination of the “optical” diffusion coefficient ( D op), enabling analysis of the Li + diffusion rate and, consequently, the coloration front rate in these host matrices. The D op values within the WO 3/chitosan/PEO film were significantly higher than those within the WO 3/chitosan film, mainly for higher values of injected charge. The presence of PEO also ensured larger accessibility to the electroactive sites, in accordance with the method employed here. Hence, this spectroelectrochemical method allowed us to separate the contribution of the diffusion process from the number of accessible electroactive sites in the materials, thereby aiding a better understanding of the useful electrochemical and electrochromic properties of these films for use in electrochromic devices.

Color Control in π-Conjugated Organic Polymers for Use in Electrochromic Devices

Color Control in π-Conjugated Organic Polymers for Use in Electrochromic Devices

Electrolytes based on LiClO 4 and branched PEG–boronate ester polymers for electrochromics

Structure–property relationships of polymers incorporating Lewis acidic boron in their branched chain architecture were investigated as a function of LiClO 4 salt concentration. The polymers were synthesised from boron trioxide, and different poly(ethylene glycol)s (PEGs) and monomethyl ether end-capped PEGs. The PEG–boronate ester polymers based on PEGs having molecular weights equal to, or below, 300 g/mol were found to be amorphous, colourless, and highly transparent. Electrolytes derived from these polymers and LiClO 4 reached ionic conductivities up to 10 −4 S cm −1 at room temperature, and were thermally stable up to at least 150 °C. A number of electrolytes showed a combination of attractive properties which made them interesting for use in electrochromic devices.

"Stapled" bis(phthalocyaninato)niobium(IV), Pc2Nb: X-ray crystal structure, chemical and electrochemical behavior, and theoretical studies. Perspectives for the use of Pc2Nb (thin films) as an "optically passive electrode" in electrochromic devices.

Recrystallization of the previously reported monosolvated bis(phthalocyaninato)niobium(IV), [Pc2Nb].CINP (CINP = 1-chloronaphthalene), has allowed isolation of a single crystal of a new solvated form, i.e. [Pc2Nb]. 3.5CINP, whose structure has been elucidated by X-ray work: space group P2(1)/n (No. 14); a = 16.765(3), b = 23.800(4), c = 19.421(4) A; alpha = gamma = 90 degrees, beta = 92.51(2) degrees; Z = 4. The sandwiched material is a "stapled" molecule, characterized by the presence of two intramolecular interligand C-C sigma bonds and highly strained phthalocyanine units, as formerly observed by crystallographic work for its Ti(IV) analogue, [Pc2Ti], and the +1 corresponding fragment, [Pc2Nb]+, present in the species [Pc2Nb](l3)(l2)0.5.3.5CINP. [Pc2Nb] appears to be reluctant to undergo further oxidation above the +1 oxidation state. Detailed theoretical studies by DFT and TDDFT methods have been developed on [Pc2Nb] and [Pc2Nb]+, also extended for comparison to the Ti(IV) complex [Pc2Ti], and an adequate picture of the ground-state electronic structure of these species has been achieved. Moreover, the excitation energies and oscillator strengths calculated for the closed-shell systems, [Pc2Ti] and [Pc2Nb]+, provide a satisfactory interpretation of their characteristic visible optical spectra and help to rationalize the similar features observed in the visible spectrum of the open-shell "stapled" complex, [Pc2Nb]. Thin solid films (100-250 nm) of [Pc2Nb] deposited on ITO (indium-doped tin oxide) show a reversible redox process in neutral or acidic aqueous electrolytes. The electrochemical and electrochromic properties of the sandwiched complex, combined with impedance and UV/visible spectral measurements, are presented and discussed. The achieved electrochemical information, while substantially in keeping with the observed chemical redox behavior and theoretical predictions, qualifies [Pc2Nb] as an "optically passive" electrode and a promising material for its use in electrochromic devices.

Spectroelectrochemical studies of manganese phthalocyanine thin films for applications in electrochromic devices

The spectroelectrochemical properties of manganese phthalocyanine (MnPc) thin films are studied. Cyclic voltammetry (CV) and UV–vis in situ spectroelectrochemistry were done to characterize the MnPc thin films. In this study, the insertion of cations during the reduction of MnPc thin films is proposed. Two reversible redox pairs were observed at 0 and −0.9 V (vs. Ag ∣ AgCl) as judged by CVs. According to the absorption spectral data, the reaction at 0 V is related to the transformation between [Mn IIIPc 2−] and [Mn IIPc 2−], and the reaction at −0.9 V is attributed to the transformation between [Mn IIPc 2−] and [Mn IPc 2−]. The polychromic characteristics of MnPc thin films were also observed under different redox potentials and can be expressed as follows: 0.5 (light green)→−0.5 (green)→−0.9 (greenish blue)→−1.0 V (purple). The electrochromism of MnPc thin films for use in electrochromic devices (ECD) is also discussed. A complementary ECD, comprising a MnPc and polyaniline (PAni) thin film couple was constructed. This device was darkened and bleached using −1.0 and +1.0 V, respectively. The color of the device was changed from light green to green and the transmittance of the device varied from 60 to 17% at 550 nm.

Proton conducting composite electrolytes based on antimonic acid

This report concerns a composite proton electrolyte suitable for use in electrochromic devices. The electrolyte consists of nanosize pyrochlore antimonic acid particles suspended in a poly(vinyl acetate) matrix by a gel route. It was found possible to substitute the antimonic acid by inert oxides of aluminum and silicon, thus making the electrolyte less harmful to the oxide electrodes of the electrochromic devices without considerably decreasing the conductivity. The proton conductivity of the antimonic acid electrolyte was ∼10 −4 S/cm at room temperature, practically independent of its amount of absorbed water.

Thin film of lithium niobium oxynitride as ionic conductor

A novel glassy ionic conductor, lithium niobium oxynitride, was prepared in form of thin films and characterized. Thin-film deposition was carried out by rf magnetron sputtering of LiNbO3 target in nitrogen-containing atmosphere. These films exhibit ionic conductivity of two orders higher than that of LiNbO3 films, the room-temperature conductivity being about 5×10−7 S cm−1. Film structure is highly cross linked, leading to activation energy as low as 0.5 eV. Film transmittance is higher than 85% in both the visible and solar ranges, making them also suitable for use in electrochromic devices.

Polymer-based electrochromic devices

Electrochromic phenomena related to p-doping-undoping process of thiophene-based polymers are briefly described. Electrochromic performance data of poly(2,2'-bithiophene) and poly(3-methylthiophene) polymers, electrosynthesized from 2,2'-bithiophene and 3-methylthiophene commercial products in optimized conditions, to evaluate the possibility of their use in electrochromic devices are surveyed, and the test results of a poly(3-methylthiophene)-based electrochromic device operating in transmissive mode with counter electrode optically passive are reported. Finally, electrochromic performance data of 3-methylthiophene polymers with “tailor-made” conjugation length through electrochemical polymerization of 3-methylthiophene dimers are reported and discussed.