Electrochromic Layer Research Articles

The improvement of all-solid-state electrochromic devices fabricated with the reactive sputter and cathodic arc technology

The all-solid-state electrochromic device (ECD) with the one substrate structure fabricated by the reactive dc magnetron sputtering (DCMS) and cathodic vacuum arc plasma (CVAP) technology has been developed for smart electrochromic (EC) glass application. The EC layer and ion conductor layer were deposited by reactive DCMS and CVAP technology, respectively. The ion conductor layer Ta2O5 deposited by the CVAP technology has provided the better porous material structure for ion transportation and showed 1.76 times ion conductivity than devices with all sputtering process. At the same time, the EC layer WO3 and NiO deposited by the reactive DCMS have also provided the high quality and uniform characteristic to overcome the surface roughness effect of the CVAP ion conductor layer in multilayer device structure. The all-solid-state ECD with the CVAP ion conductor layer has demonstrated a maximum transmittance variation (ΔT) of 55% at 550nm and a faster-switching speed. Furthermore, the lower equipment cost and higher deposition rate could be achieved by the application of CVAP technology.

Sputtered Si3N4 and SiO2 electron barrier layer between a redox electrolyte and the WO3 film in electrochromic devices

The application of a redox electrolyte in hybrid type electrochromic devices allows a high charge capacity, thereby a high optical contrast can be achieved. However, the current between the redox electrolyte and the electrochromic layer (tungsten oxide, WO3) interface in equilibrium at colored state of device is critical for a window with large area. This loss current should be maintained below 10μA/cm2 to avoid an inhomogeneous coloration of a large window caused by an ohmic voltage drop in transparent conductive oxide (TCO). The power consumption of such a loss current can be neglected. In this regard, we have investigated silicon nitride (Si3N4) and silicon oxide (SiO2) films as an intermediate electronic barrier layer on the top of the WO3 with thicknesses of 12, 35, 80 and 180nm. These films were coated by direct current reactive magnetron sputtering technique. The electron barrier properties were studied for the iodide/triiodide (I−/I3−) and tetramethylthiourea/tetramethylformaminium disulfide dication (TMTU/TMFDS2+) redox couples for application in electrochromic devices. For both redox couples, Si3N4 showed an effective electronic barrier layer. The thickness of 80nm of Si3N4 reduced the loss current from 240 down to 20μA/cm2 for the I−/I3− redox electrolyte with the visual (solar) transmission from 45% (33%)down to 0.7% (0.5%)at 1V.Similarly, the loss current was reduced from 70 down to 7μA/cm2with the visual (solar) transmission from 71% (54.5%) down to 3% (2%) for TMTU/TMFDS2+ redox electrolyte. However no significant reduction of loss circuit current was achieved with SiO2 barrier layer for both redox couples.

Optimized ion diffusion depth for maximizing optical contrast of environmentally friendly PEDOT:PSS electrochromic devices

Because the electrochromic (EC) performance significantly affects the diffusion of ions into the EC layer, EC layer thicknesses vary, ranging from approximately 100 nm to 400 nm. Their optimized and maximized EC performance in both optical contrast and color-switching behaviors are investigated as a function of EC layer thicknesses and applied bias voltages. Commercially available poly(3,4-ethylenedioxythiophene): poly(styrene-sulfonate) (PEDOT:PSS) is selected as the EC layer due to its environmentally friendly condition and expected reproducible uniformity. Among the four different thicknesses of the PEDOT:PSS layer fabricated, the ~200 nm thick PEDOT:PSS layer exhibits the highest optical contrast ratio at an applied bias voltage of + 3.0 V for the bleached state and - 3.0 V for the colored state. Moreover, through increasing the applied bias voltage slightly to + 3.5 V/- 3.5 V, the color-switching speed is also significantly improved from 10 s to 5 s for switching from the bleached state to the colored state.

The Effect of the Amount of Intercalated Li-Ions on the Electrochemical Performances and the Color Changes in the Electrochromic Layer

Global warming and the energy crisis have been accelerated the necessity to develop the energy saving system and to increase energy efficiency are for many researchers. For instance, smart window consisting of glass, electrochromic layer, and electrolyte is one of the promising candidates to fulfill this goal. The color change of this smart window should be delicately controlled responding to the capriciousexternal environment condition. Although many researchers have been mainly focused on the physical properties of active materials such as crystalline and morphological structures to modulate optical density of the smart window[1,2], the color difference of smart window according to amount of intercalated Li-ions in electrochromic layer has never been considered thus far. Hence, we investigated the effects of the color changes of electrochromic layer corresponding to the different amount of intercalated Li-ions. We employed three-electrode type unit cells consisting of working electrode (WO3/ITO), reference electrode (Ag/AgCl with 3M KCl), counter electrode (Pt) and electrolyte (1M LiClO4 in PC) throughout this study. We monitored the correlation between the voltage changes and the transmittance of electrochromic devices as applying a constant current as a function of the amount of the intercalated Li-ion. Furthermore, the crystalline structure of active materials was also investigated using an X-ray diffraction (XRD) technique. 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) References [1] Christopher S. Blackman and Ivan P. Parkin, Chem. Mater. 2005, 17, 1583-1590 [2] By Se-Hee Lee, Rohit Deshpande, Phil A. Parilla, Kim M. Jones, Bobby To, A. Harv Mahan, and Anne C. Dillon, Adv. Mater. 2006, 18, 763–766

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.

Fast Electrochromic Device Based on Single-Walled Carbon Nanotube Thin Films.

Optical properties of electrochromic materials can be controlled by the application of an electric field allowing recent development of new applications such as smart windows technology for indoor climate control and energy conservation. We report the fabrication of a single-walled nanotube (SWNT) thin film based electro-optical modulator controlled by ionic liquid polarization in which the active electrochromic layer is made of a film of semiconducting (SC-) SWNTs and the counter-electrode is composed of a film of metallic (MT-) SWNTs. Optimization of this electro-optical cell allows the operations with an optical modulation depth of 3.7 dB and a response time in the millisecond range, which is thousands of times faster than typical electrolyte-controlled devices. In addition, a dual electro-optical device was built utilizing electro-optically active SC-SWNT films for each electrode that allowed increasing modulation depth of 6.7 dB while preserving the speed of the response.

Prussian blue for electrochromic devices

All solid electrochromic devices (ECDs) were prepared using Prussian blue (PB) as electrochromic layer, CeO2-TiO2 as counter electrode, and either DNA-Er(CF3SO3)3 or Agar-Eu(CF3SO3)3 as ionic conductive membrane. The ECDs were assembled by combining the natural macromolecule-based electrolyte membrane placed between the glass-ITO/PB and CeO2-TiO2/ITO-glass electrodes. The two kind of electrochromic devices were characterized electrochemically and spectroscopically. The electrochemical measurements revealed that applying potentials of −3.0 and +2.0V promoted the color change of the ECD from blue to transparent. The highest contrast of ΔTVIS=25±2% was at 686nm after 60s of applied potential for ECD with DNA-Er3+-based electrolyte. This ECD showed the charge density of −5.1mCcm−2 after 15s and −10.4mCcm−2 after 60s of potential application. Although a successive chronoamperometric (CA) cycling showed the insertion/extraction processes uniform, the ΔTVIS and charge density values dropped down to 5% and −1.6mCcm−2 after 1000 CA cycles, respectively. The ECD with Agar-Eu3+-based electrolyte displayed almost the same charge density values of −5.1mCcm−2 after 15s and −10.5mCcm−2 after 60s of −3.0V potential application. This value decreased to −1.1mCcm−2 after 1400 CA cycles. The best result of ΔTVIS was of 35±2% at λ=686nm. All the presented results suggest the possibility of using PB as electrochromic coating and natural macromolecules as solid electrolyte in new ECDs development.

Novel fabrication of an electrochromic antimony-doped tin oxide film using a nanoparticle deposition system

Novel deposition method of Antimony-doped tin oxide (ATO) thin films was introduced using a nanoparticle deposition system (NPDS) to fabricate an electrochromic (EC) device. NPDS is a dry deposition method that simplifies the ATO deposition process by eliminating the need for solvents or binders. In this study, an ATO EC layer was deposited using NPDS. The surface morphology and electrochemical and optical transmittance properties were characterized. The optical transmittance change in the ATO EC device was ∼35% over the wavelength range of 350–800nm, and the cyclic transmittance was stable. The ATO film deposited using NPDS, exhibited a coloration efficiency of 15.5cm2C−1. Therefore, our results suggest that ATO EC devices can be fabricated using a simple, cost-effective NPDS, which allows nanoparticles to be deposited directly without pre- or post-processing.

Performance and reliability of cellulose acetate-based gel electrolyte for electrochromic devices

This work describes optimized conditions for the use of cellulose acetate (CA), a naturally derived polymer, in gel electrolytes (GEs) for electrochromic devices (ECDs). The GEs were doped with lithium perchlorate (LiClO4) as a supporting salt electrolyte and propylene carbonate as a solvent. The conductivity of GEs with varying CA concentration was evaluated by a conductivity meter to determine the effectiveness of electrolyte ion transport in the GE matrix. Then, we employed poly(3-hexylthiophene-2,5-diyl) (P3HT) thin films as an electrochromic layer on an ITO substrate. The P3HT film served as the main cathodic electrochromic layer, the GE as an ion conducting layer, and a piece of bare ITO substrate as an anodic electrochromic layer. We evaluated the stability of the P3HT film by measuring the optical and electrochemical properties of P3HT thin films on ITO in GEs through UV–Vis and cyclic voltammograms obtained during application of potential to the films. Current/voltage data and related performance for ECDs were investigated. The results showed that the prepared GEs have high stability within the operative potential window for ECDs. The electrochromic polymer films operated with the prepared GE showed good stability with fully reversible color change for more than 1000 cycles without polymer film or GE degradation. This work shows the first example of the use of GE with a natural polymer matrix in electrochromic devices and demonstrates their reliability under repetitive switching of applied voltage for up to 1000 cycles.

Inkjet-printed all solid-state electrochromic devices based on NiO/WO3 nanoparticle complementary electrodes.

Nanostructured thin films are important in the fields of energy conversion and storage. In particular, multi-layered nanostructured films play an important role as a part of the energy system for energy saving applications in buildings. Inkjet printing is a low-cost and attractive technology for patterning and deposition of multi-layered nanostructured materials on various substrates. However, it requires the development of a suitable ink formulation with optimum viscosity, surface tension and evaporation rate for various materials. In this study, a versatile ink formulation was successfully developed to prepare NiO and WO3 nanostructured films with strong adhesion to ITO coated glass using inkjet printing for energy saving electrochromic applications. We achieved a high performance electrochromic electrode, producing porous and continuous electrochromic films without aggregation. The NiO film with 9 printed layers exhibits an optical modulation of 64.2% at 550 nm and a coloration efficiency (CE) of 136.7 cm(2) C(-1). An inkjet-printed complementary all solid-state device was assembled, delivering a larger optical modulation of 75.4% at 633 nm and a higher CE of 131.9 cm(2) C(-1) among all solid-state devices. The enhanced contrast is due to the printed NiO film that not only performs as an ion storage layer, but also as a complementary electrochromic layer.

Electrochromic device with Prussian blue and HPC-based electrolyte

Given the importance of the development of electrochromic devices (ECDs) for technological applications small devices with Prussian blue (PB)/hydroxypropyl cellulose (HPC) electrolyte/CeO2-TiO2 configuration were assembled and characterized. The films of PB were obtained galvanostaticaly by applying −0.45μA for 300s. The cyclic voltammetry, in 1molL−1 KCl solution, of these films showed a redox pair peaks at well-defined potential of 0.16V for oxidation and 0.4V for reduction processes. The ECDs were assembled by combining the HPC-based membrane between the counter-electrode consisting of CeO2–TiO2 and the PB electrochromic layer. The devices were characterized by chronocoulometry coupled with UV–vis transmittance spectroscopy, open circuit properties, and voltammetry. The combination of PB with the transparent HPC electrolyte membrane resulted in an electrochromic device that switched between transparent and blue states by applying −2.6 and 2.0V, respectively. The charge density measurements showed an increase from −6.0 to −8.4mCcm−2 when the potentials where applied for 15 and 60s, respectively. The UV–vis spectra of the ECDs revealed that switching the ECD between −2.6 and 2.0V for 15s/15s and 60s/60s resulted in 28 and 32% of transmittance difference between both states, respectively. The memory test, i.e., the changes of transmittance in open circuit after applying a potential of -2.6V for 15 s revealed a decrease of transmittance from 60 to 59% in 3h. The cyclic voltammetry measurements performed from 20 to 500mVs−1 showed better resolutions of the oxidation and reduction peaks for higher scan rates. Moreover, it was observed that after 2000 cycles, the charge density decreased from −6.0 to −1.5mCcm−2 and the difference of transmittance between colored and bleached state decreased from 28 to 5%.

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.

Layer-by-Layer Assembly of PEDOT:PSS and WO3 Nanoparticles: Enhanced Electrochromic Coloration Efficiency and Mechanism Studies by Scanning Electrochemical Microscopy

Layer-by-layer assembly method is employed to fabricate multilayer hybrid films based on poly(styrenesulfonate)-doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) and tungsten oxide nanoparticles (WO3 NPs). Polyethylenimine (PEI) is deposited in between to introduce electrostatic force between the components. In the hybrid films, randomly oriented disk-like WO3 NPs are homogeneously distributed in the polymers and form an interdigitated structure. This very rough surface morphology hinders the formation of a continuous PEI layer between the electrochromic layers. Owing to the efficient charge transfer between the two active components and complementary electrical conductivity of the two components in the redox switching process, the coloration efficiency of the hybrid film is significantly improved to 117.7cm2/C at wavelength of 633nm. The underlying mechanism for the enhancement is verified by scanning electrochemical microscopic studies through probing the conductivity changes of PEDOT:PSS, WO3-NP and hybrid films under various applied potentials.

Integration of polyelectrolyte based electrochromic material in printable photovoltaic electrochromic module

Compared to traditional electrochromic technology, photovoltaic electrochromic (PV-EC) module can achieve color change in electrochromic layers without additional power source. In this work, an innovative printable PV-EC module is provided. The device includes a plurality of planarly distributed silicon thin film solar cells (Si-TFSCs) configured in superstrate structure, covered with a layer of polyelectrolyte based electrochromic thin film (ECTF). The Si-TFSC consists of one anode (with a portion of area exposed from the Si-TFSC), a photoelectric conversion layer, and one cathode. The ECTF is prepared from nano-size polyelectrolyte based electrochromic material, which is composed of polyaniline (PANI) and polyanion poly(sodium 4-styrenesulfonate) (PSS) nanospheres mixture. When the printable PV-EC module is irradiated by sunlight, the PANI/PSS ECTF on the surface of the transparent anode layer exhibits anodic color changing, and transforms from pale green (emeraldine salt state) to light blue (emeraldine blue state).

Simple Strategies Towards Lowering the Activation Potential of Electrochromic Devices. Case Study on TiO2-Viologen Based Displays

The purpose of this study is to demonstrate the easy tuning of the activation potential of electrochromic devices (ECDs) by varying the nature of the electrolyte and counter electrode. For this purpose ECDs with a simplified configuration were fabricated (i) by using TiO2-viologen deposited on Transparent Conducting Oxide (TCO) as electrochromic active layer (EC1) and (ii) by replacing the counter electrode consisting of an electrochromic material and a conductive one (EC2/TCO) in a traditional 5-layers battery type ECD (TCO/EC1/electrolyte/EC2/TCO) by a metal electrode. Firstly a comparison is made between polymer membrane and aqueous gel electrolytes with varying compositions, focusing on the influence of ionic conductivity on the contrast and the switching time. Low toxicity aqueous based gel electrolytes were prepared from gelatin, glycerol, and NaCl/LiCl as ion precursor, whereas the polymer membrane electrolyte consisted of 0.3M LiTFSI in BMITFSI with 40% PMMA. At the end of our study we have investigated the influence of the metal counter electrode nature, more precisely the type of metal and its surface morphology, on the devices response time and optical modulation. The use of an aqueous gel electrolyte (~10-3/-2 S/cm) instead of a membrane electrolyte (~10-4/5 S/cm) leads to lowering the working potential window; ECDs are colored at -0.5V and bleached at 0V (Fig. 1), turning from blue to white in few seconds. Also, higher contrast (DR) and shorter coloration (tc) and bleaching (tb) times are reached for electrolytes exhibiting higher ionic conductivity (σ). The morphology of the metal electrode influences mainly the coloration kinetics, and the difference is more obvious for the electrolytes with lower ionic conductivity (Fig. 1). Figure 1

Electrochromic Devices Using Prussian Blue Electrochromic Layer and HPC-Based Electrolyte

Electrochromic devices (ECDs) have been studied for technological application. The ECDs with Prussian blue (PB)/hydroxypropyl cellulose (HPC) electrolyte/CeO2-TiO2 configuration were assembled and characterized. The films of PB were obtained by galvanostatic electrodeposition applying -0.45 μA for 300 s on ITO glass immersed in a solution of 0.05 M K3Fe(CN)6, 0.05 M FeCl3×6H2O and 0.05 M HCl. The electrolyte was prepared by mixing 0.3 g of HPC with 30 mL of acetone and addition of 10 % m/m of LiClO4. To this mixture, polyethyleneglycol (PEG) also was added. The ECDs were assembled by combining the HPC membrane between the counter-electrode consisting of CeO2-TiO2 and the Prussian Blue electrochromic layer. The devices were characterized by chronocoulometry coupled with UV-Vis transmittance, open circuit properties, and voltammetric cycling. The ECD was switched transparent and blue states applying -2.6 and 2.0 V, respectively. The charge density measurements showed an increase from ~-10 to -14 mC/cm2 when the potentials where applied for 15 s and 60 s, respectively. While this potential is applied, we observe a variation of transmittance in the UV-Vis spectra region, revealing that switching the ECD between -2.6 and 2.0 V for 15 s/15 s and 60 s/60 s resulted in 27 % and 42 % of difference between both states. Changes of transmittance in open circuit after applying a potential of -2.6 V for 15 s revealed a decrease from 50% to 27 % in 24 h. The cyclic voltammetry measurements performed at 100 and 200 mV/s showed better resolutions of the oxidation and reduction peaks for higher scan rates. Moreover, it was observed that after 1,000 cycles, the charge density decreased from -10 to -6.9 mC/cm2 and the difference of transmittance between colored and bleached state decreased from 41 to 30 %. The obtained results revealed that Prussian blue with HPC electrolyte are very promising materials for ECD applications. …

Surface Treatments for Electrochromic Glazing: Toward Reduced Costs and Optimal Performances through Ultrasonic Spray Pyrolysis

Research and industrial interests for electrochromic “smart” windows have considerably grown those recent years due to their potential use as an energy-saving material for buildings. Their CO2 emission can be significantly reduced by decreasing their energy consumption up to 30%. The crucial issues of such devices are the coloration efficiency as well as the reversibility upon coloration and bleaching of the electrochromic layers. The combination of WO3 and Li-doped NiO surface films (separately as working and counter electrodes) affords a good coloration contrast between colored and bleached states of the device, since tungsten oxide colors upon electrons and ions insertion while nickel oxide gets colored after their extraction. In order to improve the performances of those electrochromic films, we have studied the effects of a surfactant-assisted deposition process of both individual layers through Ultrasonic Spray Pyrolysis (USP). This technique indeed constitutes a low-cost alternative to industrial vacuum processes for manufacturing high quality thin films. The crystallization and morphology of those films, as well as their optical, electrochromic and electrochemical properties have been investigated. The presence of surfactant in the precursor solution has led to improved wetting of liquid droplets sprayed on the heated FTO/glass substrate. The resulting films testify for a better homogeneity and a higher active surface, which also allows for enhanced reversibility and coloration contrast.

Fibroin Films Doped with Lithium Ions for Application in Electrochromic Devices

Silk fibroin is a commonly available natural biopolymer produced in specialized glands of arthropods, with a long history of use in textile production and also in health cares. The exceptional intrinsic properties of these fibers, such as self-assembly, machinability, biocompatibility, biodegradation or non-toxicity, offer a wide range of exciting opportunities [1]. Silk research is mainly devoted regarding the biomaterials field. Although, it has long been recognized that silk is can be a rich source of inspiration for designing new materials with tailored properties, enhanced performance and high added value for targeted applications, opening exciting new prospects in the domain of materials science and related technological fields, including bio-friendly integration, miniaturization and multifunctionalization. Progresses in new technological fields such as optics, photonics and electronics are emerging [2,3]. The incorporation of polymer electrolytes as components of various devices (advanced batteries, smart windows, displays and super-capacitors) offers significant advantages relative to traditional electrolytes, including enhanced reliability and improved safety. Preliminary tests performed with a prototype electrochromic device (ECD) incorporating the most promising electrolyte composition, silk fibroin films doped with lithium ions (LiTFSI and LiBF4) as electrolyte and WO3as cathodic electrochromic layer, are extremely encouraging. Acknowledgements: This work was supported by Fundação para a Ciência e a Tecnologia (FCT) and Feder (contracts PTDC/CTM-BPC/112774/2009, PEst-OE/QUI/UI0616/2014 and PEst-C/QUI/UI0686/2013) and COST Action MP1202 “Rational design of hybrid organic-inorganic interfaces”. R.F.P.P. acknowledges FCT and program POPH/FSE for a grant (SFRH/BPD/87759/2012). COST Action MP1202 “Rational design of hybrid organic-inorganic interfaces”.M. M. Silva acknowledges CNPq, for the mobility grant provided by this institution.

Gellan gum—Ionic liquid membranes for electrochromic device application

Biopolymer-based materials have been of particular interest and they are alternatives to synthetic polymers based on the decreasing oil resources. The polymer electrolytes were doped with choline-based IL N,N,N-trimethyl-N-(2-hydroxyethyl)ammonium bis(trifluoromethylsulfonyl)imide ([N1 1 1 2(OH)][NTf2]), or Er (CF3SO3)3 or both. The polymer electrolytes were employed in the production of glass/ITO/WO3/electrolyte/CeO2–TiO2/ITO/glass electrochromic devices (ECDs). The lowest onset temperature for the degradation of all the SPEs is at ~130°C for the Gellan Er (CF3SO3)3 (10:1) this temperature range of stability is wide enough for a material to be applied as an electrolyte/separator component in electrochemical devices.The three ECDs displayed fast switching speed (ca. 15s). Gellan [N1 1 1 2(OH)][NTf2] Er (CF3SO3)3 (5:1:10) exhibited an electrochromic contrast of 4.2% in the visible region, the coloration efficiency attained at 555nm was 3.5 and 0.90cm-2C-1 in the “colored” and “bleached” states, respectively, and the open circuit memory was 48h. Preliminary tests performed with a prototype electrochromic device (ECD) incorporating WO3 as cathodic electrochromic layer, are extremely encouraging.

Spectroscopic and microscopic study of Prussian blue film for electrochromic device application

All solid electrochromic devices (ECDs) were prepared using Prussian blue (PB) as electrochromic layer, CeO2-TiO2 as counter electrode and poly(vinylidene difluoride) (PVDF) as ionic conductive membrane. The electrodeposited PB films were characterized by ellipsometry and the thickness, roughness and refractive index of 217nm, 1.9nm and 1.5808, respectively, were obtained. The ECDs were assembled by combining the PVDF-based electrolyte membrane between the ITO-glass/CeO2-TiO2 and PB/ITO-glass electrodes. From the electrochemical measurements, it was stated that applying potentials of +1.5 and −2.8V promoted the color change of the ECD from blue to transparent. The UV–vis transmittance spectra revealed that applying 15s/15 s and 60s/60 s square wave of −2.8 and 2.0V resulted in the difference of 15.9 and 39.6% between both states, respectively. Moreover, the charge density values increased from ∼7 to ∼10mCcm−2, after applying −2.8V for 15 and 60s, respectively. The memory test of the ECD performed in open circuit, after applying −2.8V for 15s, revealed a decrease of transmittance from 37.5 to 21% in 24h. The cyclic voltammetry performed at 100mVs−1, evidenced the reduction at −0.1V and oxidation at 0.4V peaks, responsible for PB color change. Additionally, it was stated that after 500 chronoamperometric cycles, the charge density values decreased from −4.8 to −1.9mCcm−2. Finally, the presented results suggest the possibility of using PB as electrochromic coating and PVDF as solid electrolyte in new ECDs development.