Morphology effect on the electrochromic and electrochemical performances of NiO thin films

NiO thin films on ITO substrate were prepared by chemical bath deposition (CBD) and sol–gel method, respectively. The microstructure and morphology of the NiO films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Both the films have polycrystalline cubic NiO, but have distinct morphology. The CBD NiO thin film with a highly porous structure exhibited a noticeable electrochromic performance. The variation of transmittance was high up to 82% at 550 nm and the coloration efficiency (CE) was calculated to be 42 cm² C⁻¹. The sol–gel NiO thin film with a smoothly compact structure presented 35% and 28 cm² C⁻¹ at 550 nm, respectively. The electrochemical properties of both the NiO thin films were investigated in 1 M KOH electrolyte by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The CV and EIS measurements revealed that the CBD NiO thin film had better electrochemical reversibility, higher reactivity and reaction kinetics due to its highly porous structure.     

Enhanced electrochromic properties of ordered porous nickel oxide thin film prepared by self-assembled colloidal crystal template-assisted electrodeposition

Highly ordered porous NiO film is prepared by self-assembled monolayer polystyrene sphere template-assisted electrodeposition. The as-prepared NiO film shows an ordered hexagonal close-packed bowel-like array that is made up of macrobowls with about 500 nm in diameter. The electrochromic properties of NiO film are investigated in an aqueous alkaline electrolyte (0.1 M KOH) by means of transmittance, cyclic voltammetry and chronoamperometry measurements. The ordered porous NiO film prepared with PS sphere template exhibits a noticeable electrochromism with reversible color changes from transparent to dark brown, and presents quite good transmittance modulation with a variation of transmittance up to 76% at 550 nm. The ordered porous NiO film also shows high coloration efficiency (41 cm² C⁻¹), fast switching speed (3 s and 6 s) and good cycling performance, compared with the dense NiO film prepared without PS sphere template. The improvements of electrochromic performances are attributed to the highly porous morphology, which shortens the ion diffusion paths and provides bigger surface area.     

Sol-gel fabrication of NiO and NiO/WO3 based electrochromic device on ITO and flexible substrate

Electrochromic devices (ECDs) with reversible transmittance change represent a promising alternative to smart windows. However, the low−cost facile fabrication of ECDs, particularly flexible devices, remains challenging. In this study, novel NiO is synthesized by a solid state method, and the as−prepared NiO is introduced as an electrochromic anodic layer and fabricated onto a transparent conductive electrode (indium tin oxide, ITO or flexible silver nanowires, AgNW) by a sol–gel spin coating and low temperature annealing (80 °C-150 °C). The solvent, thickness of NiO, and annealing temperature are evaluated to obtain higher ECD performance. NiO/ITO ECDs exhibit very high transmittance variation (ΔT = ~84%) at 700 nm with applied potentials of −3.0 and 0 V. The stability and transmittance variation of NiO/ITO are significantly improved in the presence of a WO₃ cathodic electrode at lower applied voltages of 1.5 to 0 V. The low processing temperature of 80 °C demonstrates the potential of the flexible ECDs. The flexible NiO–WO₃ device achieves a transmittance variation of ~38% at 700 nm with applied potential of 2.0 and 0 V, and retains the ECD performance. The application of low−cost solution−processed NiO and NiO/WO₃−based ECDs in flexible transparent conductive electrodes provides a new pathway for the fabrication of optical devices and printed electronics.     

Simple and rapid synthesis of NiO/PPy thin films with improved electrochromic performance

Nickel oxide/polypyrrole (NiO/PPy) thin films were deposited by a two step process in which the NiO layer was electrodeposited potentiostatically from an aqueous solution of NiCl₂·6H₂O at pH 7.5 on fluorine doped tin oxide (FTO) coated conducting glass substrates, followed by the deposition of polypyrrole (PPy) thin films by chemical bath deposition (CBD) from pyrrole mixed with ammonium persulfate (APS). The NiO/PPy films were further characterized for their structural, optical, morphological and electrochromic properties. X-ray diffraction study indicates that the films composed of polycrystalline NiO and amorphous PPy. Infrared transmission spectrum reveals chemical bonding between NiO and PPy. Rectangular faceted grains were observed from scanning electron microscopy results. The electrochromic (EC) property of the film was studied using cyclic voltammogram (CV), chronoamperometry (CA) and optical modulation. The NiO/PPy presents superior EC properties than their individual counterparts. The coloration/bleaching kinetics (response time of few ms) and coloration efficiency (358 cm²/C) were found to be improved appreciably. The dramatic improvement in electrochemical stability (from about 500 c/b cycles for PPy to 10,000 c/b cycles for NiO/PPy) was observed. This work therefore demonstrates a cost-effective and simple way of depositing highly efficient, faster and stable NiO/PPy electrodes for EC devices.     

Influence of Ag incorporation on the structural,optical and electrical properties of ITO/Ag/ITO multilayers for inorganic all-solid-state electrochromic devices

Indium tin oxide/silver/indium tin oxide (ITO/Ag/ITO, IAI) multilayer structures were prepared by DC magnetron sputtering as a conductive transparent electrode for inorganic all-solid-state electrochromic devices. A thin layer of silver (Ag) with various thicknesses was inserted between two layers of ITO films. The XRD and SEM results revealed that the microscopic morphology of Ag film was closely related to the thickness. Besides, the electrical and optical properties of the IAI multilayers were significantly influenced by the Ag layer thickness. The optimized IAI multilayers demonstrated the best combination of electrical and optical properties with a figure of merit of 54.05 (sheet resistance of 6.14 Ω/cm²and optical transmittance of 90.83%) when the Ag film was 10 nm thick. In order to evaluate the IAI multilayers as a transparent electrode for electrochromic applications, two ECDs with the structures of ITO/NiO_x/LiPON/WO₃/ITO and ITO/NiO_x/LiPON/WO₃/IAI were prepared, and their electro-optical properties were characterized by cyclic voltammetry (CV), chronoamperometry (CA) and spectroscopic measurements. Compared with ECD the pure ITO top electrode (ITO/NiO_x/LiPON/WO₃/ITO), the ECD with the IAI top electrode (ITO/NiO_x/LiPON/WO₃/IAI) presented a slightly smaller optical modulation amplitude, but a faster switching speed. All our findings indicate that the IAI multilayer structure is a promising alternative to the ITO thin film for inorganic all-solid state electrochromic applications.     

Electrochromic properties of Al doped B-subsituted NiO films prepared by sol–gel

In this paper, Al doped B-substituted NiO films were prepared by sol–gel method. The effect of the Al content on the structure of the Al_xB_0.15NiO films were studied with X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrochemical and EC properties were examined by cyclic voltammetric (CV) measurements and UV–Vis spectrophotometry, respectively. Al doping could prevent the crystallization of the films, which exhibited much better electrochemical and electrochromic properties than undoped samples. The bleached state absorbance could be significantly lowered when the Al added. EC efficiencies measured at λ = 500 nm of the films with different Al doping content reach ～30 cm² C^?1, with a change in transmittance up to 70%.     

Effect of Ar/O2 ratio on double-sided electrochromic glass performance

This paper reports the qualities of WO₃ film and NiO film added to a counter electrode and their use in a double-sided electrochromic glass device. A mixture of argon and oxygen gasses with ratios of Ar/O₂ of 1.5, 2, 3, and 5 were used for the deposition of the working electrode of WO₃ film for EC glass. The structure of double-side EC glass consists of glass/ITO/NiO/electrolyte/WO₃/ITO/glass/ITO/WO₃/electrolyte/NiO/ITO/glass layers. The working electrode of WO₃ film controls the color presented, the applied voltage controls the color depth, and the counter electrode controls the transparency in the bleached state. The double-sided EC glass with double WO₃ films and double NiO films have faster coloration/bleaching rates than do single-sided EC glass. A mixture of Ar/O₂ ratio of 3.0 has the best coloration/bleaching property of the ratios tested. Compared to the single-sided EC glass, the double-sided EC glass has lower transmittance of about 72% and 6% than the 78% and 12% during coloration and bleaching states in the visible light region with +1.5 V and ?3.5 V applied.     

Fast electrochromic response and high coloration efficiency of Al-doped WO3 thin films for smart window applications

Herein, vertically aligned Al:WO₃ nanoplate arrays were directly grown on ITO glass by a facile electrodeposition method and annealed in an argon atmosphere at 450 °C for 2h. Besides, this study reports the influence of Al doping on the electrochromic properties of WO₃ film in detail. Electrochromic properties such as cyclic voltammetry, chronoamperometry and optical transmittance were analyzed by protonic insertion/extraction in the 1 M LiClO₄/propylene carbonate as an electrolyte. The noticeable reversible color changing from transparent to the blue can be realized under the potential bias of ±1.0 V. XRD studies show that the produces films have highly crystalline structure. The EDS results clearly confirm the incorporation of Al element into the WO₃ network. From the optical absorption measurement, direct band gap energies are calculated as 3.62 and 3.34 eV for the WO₃ and the Al:WO₃, respectively. Compared to the as-prepared WO₃, the Al:WO₃ film exhibits outstanding electrochromic performance, including wide optical modulation (55.9%), high coloration efficiency (148.1 cm²C^-1), quick reaction kinetics (1.23 s and 1.01 s for colored and bleaching times, respectively), good rate capability and cycle durability at a wavelength of 632.8 nm. EIS measurements based on a charge-transfer resistance reveal that the dramatic improvement in the electrochemically active surface is achieved in the Al:WO₃ film. The increase of active surface facilitates transport kinetics for electron and ion intercalation/deintercalation within the porous metal oxide to enhance coloration efficiency. Comparatively energy levels of the WO₃ and the Al:WO₃ electrochromic films are also represented. From the Mott-Schottky studies, it is estimated that the donor concentration of the films is of the order of 10²⁰ cm⁻³. Taken together, these results not only provide important insight into a promising electrode for electrochromic displays applications, but also offer an economic and effective strategy for manufacturing of other doped metal oxide films.     

W18O49/PET-ITO柔性电致变色薄膜制备及其变色性能

采用溶剂热法制备W18O49纳米线电致变色材料，喷涂在聚对苯二甲酸乙二醇酯?氧化铟锡(PET?ITO)(方阻35 Ω)柔性透明导电基底上得到柔性电致变色薄膜。采用X射线衍射仪、扫描电子显微镜、高分辨场透射电子显微镜和X射线光电子能谱对W18O49的微观结构和价态等进行表征，用电化学工作站与紫外?可见光分光光度计对W18O49/PET?ITO柔性电致变色薄膜的光学调制范围、响应时间和循环稳定性等进行了表征和分析。结果表明，光谱扫描波长?=633 nm时，W18O49/PET?ITO柔性电致变色薄膜的光学调制范围ΔT=23%。薄膜透光率变化90%时，着色和褪色时间分别为12.8和10.6 s。W18O49/PET?ITO柔性电致变色薄膜具有优异的循环稳定性，连续着色褪色循环3000 s薄膜透光率仍达80.9%。     

Improved electrochromic performance of hierarchically porous Co3O4 array film through self-assembled colloidal crystal template

A hierarchically porous cobalt oxide (Co₃O₄) array film, in which the skeleton is composed of ordered non-close-packed bowl array possessing nanoporous walls, is successfully prepared by electrodeposition through self-assembled monolayer polystyrene sphere template. As an anodic coloring material for electrochromic application, the hierarchically porous Co₃O₄ array film exhibits enhanced electrochromic properties with higher optical modulation, faster switching speed and better cycling performance, compared to dense Co₃O₄ film. The porous Co₃O₄ array film presents a quite good transmittance modulation with 42% in the visible range and also shows good reaction kinetics with fast response time of about 2 s, much higher than those of the dense film (25% and 4.5 s). The better electrochromic performances of the porous film are attributed to its highly porous morphology, which shortens the ion diffusion paths and provides bigger surface area.     

Solvothermally grown WO3·H2O film and annealed WO3 film for wide-spectrum tunable electrochromic applications

Tungsten trioxide (WO₃) is a classical electrochromic (EC) material with advantages of abundant reserves, high coloration efficiency and cyclic stability. However, WO₃ films are often accompanied by a narrow spectrum of modulation due to a single-color change from transparent to blue. In this work, we report a wide-spectrum tunable WO₃·H₂O nanosheets EC film solvothermally grown on fluorine-doped tin oxide (FTO) glass. Interestingly, the crystalline WO₃·H₂O nanosheets film is transformed into amorphous WO₃ after annealing at 250 °C for 1 h. The amorphous film can be transformed into crystalline WO₃ film by increasing the annealing temperature to 450 °C. After annealing at 250 °C, the WO₃ film exhibits an optical modulation of 75.8% in a broad solar spectrum range of 380–1400 nm and blocks 88.9% of solar irradiance. Fast switching responses of 4.9 s for coloration and 6.0 s for bleaching, and a coloration efficiency of 86.4 cm² C⁻¹ are also achieved. Additionally, the WO₃ film annealed at 250 °C also demonstrates an excellent cyclic stability, where 99.6% of the initial optical modulation can be retained after 1500 cycles. This simple and mild solvothermal method used in this work provides a new idea for the preparation of wide-spectrum tunable WO₃ EC films.     

不同工艺对PANI/PAA复合薄膜的电致变色性能影响

采用直接聚合法与逐层镀膜法分别成功制备了聚苯胺(PANI)/聚丙烯酸(PAA)复合薄膜,通过SEM、FTIR考察了两种工艺制备的薄膜的形貌和微结构,并测定了两种复合薄膜的循环伏安性能(CV)、电流响应特性(CA)及电致变色性能。结果表明,SEM与FTIR证实了两种方法制备的PANI/PAA复合薄膜仅在材料结构上有所不同;直接聚合法制备的PANI/PAA复合薄膜(PANI/PAA-DP)表面具有较大颗粒,两对明显的氧化还原峰,氧化态和还原态的响应时间分别为120 ms和226 ms,在600～700 nm波长处的透过率调制幅度为10%;逐层镀膜法制备的PANI/PAA复合薄膜(PANI/PAA-LP)具有多孔的网络结构,3对氧化还原峰,氧化还原反应更明显,电致变色性能更优异,其氧化态和还原态的响应时间分别为45 ms和67 ms,在600～700 nm波长处的透过率调制幅度可达40%。     

不同工艺对PANI/PAA复合薄膜的电致变色性能影响研究

采用直接聚合法与逐层镀膜法分别成功制备了聚苯胺(PANI)/聚丙烯酸(PAA)复合薄膜,通过扫描电镜(SEM)、傅里叶变换红外光谱(FT-IR)等方法考察了两种工艺制备的薄膜的形貌和微结构,并测定了两种复合薄膜的循环伏安性能(CV)、电流响应特性(CA)及电致变色性能。结果表明,SEM与FT-IR证实了两种方法制备的PANI/PAA复合薄膜仅在材料结构上有所不同;直接聚合法制备的PANI/PAA复合薄膜(PANI/PAA-DP)表面具有较大颗粒,2对明显的氧化还原峰,氧化态和还原态的响应时间分别为120ms和226ms,在600~700nm波长处的透过率调制幅度为10%;逐层镀膜法制备的PANI/PAA复合薄膜(PANI/PAA-LP)具有多孔的网络结构,3对氧化还原峰,氧化还原反应更明显,电致变色性能更优异,其氧化态和还原态的响应时间分别为45ms和67ms,在600~700nm波长处的透过率调制幅度可达40%。     

Synthesis of high-performance electrochromic thin films by a low-cost method

Metal-doping is an effective method to adjust the physical and chemical properties of semiconductor metal oxides. This work adopts a simple solvothermal method to synthesize Mo-doped tungsten oxide nanoparticles. The high-performance electrochromic films can be homogenously formed on ITO glass without post-annealing. Compared with pure WO₃ films, the optimized Mo-doped WO₃ films show improved electrochromic properties with significant optical contrast (68.3% at 633 nm), the short response time (6.3 s and 3.9 s for coloring and bleaching, respectively), and excellent coloration efficiency (107.2 cm² C^?1). The improved electrochromic behavior is mainly due to the increasing diffusion rate of Li⁺ in Mo-doped WO₃ films (increased 20% than that of pure WO₃ films). The porous surface of Mo-doped WO₃ film shortens the diffusion path of Li⁺. Besides, Mo doping reduces the resistance and improves conductivity. Furthermore, 2at% Mo-doped WO₃ films indicate satisfactory energy-storage properties (the specific capacitance is 73.8 F g^?1), resulting from the enhanced electrochemical activity and fast electrical conductivity. This work presents a practical and economical way of developing high-performance active materials for bifunctional electrochromic devices.     

基于WO3-MoO3和TiO2/CdS复合电极的光电致变色器件

电致变色广泛应用于智能窗领域,但电致变色材料仍需外部电源驱动,将太阳能电池与电致变色材料结合起来的光电致变色器件可实现无需外部供电的智能变色调控。性能优异的变色阴极和光阳极是当下光电致变色器件的研究热点。通过水热法制备WO₃-MoO₃薄膜,研究其电致变色性能;通过水热法结合连续离子层沉积法制备TiO₂/CdS复合薄膜,研究其光电转换性能。最后将WO₃-MoO₃薄膜和TiO₂/CdS复合薄膜分别作为光电致变色器件的变色阴极、光阳极构建WO₃/MoO₃-TiO₂/CdS光电致变色器件。WO₃/MoO₃-TiO₂/CdS光电致变色器件具有较大的光学调制范围(630nm处为41.99%)、更高的着色效率(35.787%),将其作为智能窗应用在现代建筑、通行工具等领域具有重要应用价值。     

Nanocrystalline NiO thin film anode with MgO coating for Li-ion batteries

The nanocrystalline NiO thin films with the mean size of 30 nm are prepared by pulsed laser reactive ablation in an oxygen ambient and subsequent coated by MgO on the NiO film surface. As compared with bare NiO, coated NiO film electrode heat-treated at 500 °C exhibits excellent structural stability and electrochemical performance. Excellent electrochemical performance, a reversible capacity as high as 650 mAh/g in the range 0.01–3.0 V at high discharge rate of 2C with a high capacity retention up to 150 cycles, could be achieved with MgO-coated NiO films. Preliminary electrochemical cycling measurements show that capacity retention with capacity fading for bare NiO and MgO-coated NiO film electrodes are 0.43 and 0.28% per cycle, respectively, at the discharge rate of 2C after 150 cycles. This result is related to good structural stability of the MgO-coated NiO film as verified by cyclic voltammetric (CV) measurement and scanning electron microscopy (SEM) analysis.     

Electrochromic Nb-doped WO3 films: Effects of post annealing

The Nb-doped WO₃ films were deposited by e-beam co-evaporation method using ceramic WO₃ targets and metal Nb slugs. The films were analyzed by glancing incident angle X-ray diffraction (GIAXRD), UV/visible spectrophotometer, electrochemical cyclic voltammetry, X-ray photoelectron spectroscopy (XPS). The as-prepared film is brown and amorphous in structure. The film has low transmission in optical visible region. The XPS results indicate that the as-deposited film is non-stoichiometric. By applying a negative potential, the as-deposited film does not show obvious electrochromic effect. However, the electrochromic properties of Nb-doped WO₃ films are improved by post annealing treatment at 350, 400, and 450 °C in oxygen atmosphere. The Nb-doped WO₃ films transform into crystalline structure and become transparent after post annealing treatment. The energy band gap, optical modulation, and color efficiency increase with annealing temperature.     

Enhanced electrochromic performance of macroporous WO3 films formed by anodic oxidation of DC-sputtered tungsten layers

Self-organized macroporous tungsten trioxide (WO₃) films are obtained by anodic oxidation of DC-sputtered tungsten (W) layers on 10 mm × 25 mm indium tin oxide (ITO)-coated glass. Under optimized experimental conditions, uniformly macroporous WO₃ films with a thickness of ca. 350 nm are formed. The film shows a connected network with average pore size of 100 nm and a pore wall thickness of approximately 30 nm. The anodized film becomes transparent after annealing without significant change in macroporous structure. In 0.1 M H₂SO₄, the macroporous WO₃ films show enhanced electrochromic properties with a coloration efficiency of 58 cm² C⁻¹. Large modulation of transmittance (∼50% at 632.8 nm) and a switching speed of about 8 s are also achieved with this macroporous film.     

Porous NiO/Ag composite film for electrochemical capacitor application

A highly porous NiO/Ag composite film is prepared by the combination of chemical bath deposition and silver mirror reaction. The as-prepared NiO/Ag composite film has an interconnecting reticular morphology made up of NiO flakes with highly dispersed Ag nanoparticles of about 6 nm. The pseudocapacitive behavior of the NiO/Ag composite film is investigated by cyclic voltammograms (CV) and galvanostatic charge–discharge tests in 1 M KOH. The NiO/Ag composite film exhibits weaker polarization, higher specific capacitance and better cycling performance as compared to the unmodified porous NiO film. The specific capacitance of the porous NiO/Ag composite film is 330 F g⁻¹ at 2 A g⁻¹ and 281 F g⁻¹ at 40 A g⁻¹, respectively, much higher than that of the unmodified porous NiO film (261 F g⁻¹ at 2 A g⁻¹ and 191 F g⁻¹ at 40 A g⁻¹). The enhancement of pseudocapacitive properties is due to highly dispersed Ag nanoparticles in the composite film, which improves the electric conductivity of the film electrode.     

Effects of ethylene-acrylic acid ionomer on thermomechanical and electrochromic properties of electrochromic devices using gelatin-based electrolytes

Transparent adhesive polymer electrolytes, to be used for fabrication of electrochromic glass via a lamination process, were developed from gelatin blended with ethylene-acrylic acid (EAA) copolymer ionomer resin. The gelatin-based electrolyte films were prepared by mixing the polymer with glycerol, LiClO₄, formaldehyde, and EAA in a microcompounder. The concentration effect of EAA (i.e., 2.5, 5, 10, and 20 wt% with respect to the gelatin) on thermomechanical, optical, and electrochemical properties of the prepared films were then studied. Results from atomic force micrographs revealed that surface roughness of the neat gelatin film significantly decreased after blending with 20 wt% EAA. This corresponds to the highest ionic conductivity value (4.46 × 10⁻⁶ S/cm) of gelatin-based electrolyte in this study. Percentage light transmittance was also maintained above 80%, provided that the concentration of ionomer was kept below 20%. Finally, performance of the electrochromic device with a configuration of ITO/WO₃/gelatin/NiO/ITO was demonstrated. Coloration efficiency and response time of 60.38 cm²/C and 10 s/50 s (coloring/bleaching) were achieved, respectively.