WO3薄膜制备及其电致变色性能研究

采用直流反应磁控溅射方法在室温下制备WO3薄膜。研究溅射功率对WO3薄膜结构及电致变色性能的影响规律,考察退火后WO3薄膜的结构演变及电致变色性能变化。结果表明溅射功率为270W时薄膜表现出较好的电致变色性能,其调制幅度达78.5%,着色时间为9s,褪色时间为3.2s。将该功率下制备的WO3薄膜进行退火处理,其结构由非晶态转变为晶态,但调制幅度、响应时间特性都发生一定程度的退化。非晶态WO3薄膜相比晶态结构具有更快的响应时间和更宽的调制幅度,但晶态薄膜具有更好的循环稳定性。     

中频磁控溅射制备氧化钨薄膜及电致变色性能研究

采用中频磁控溅射方法,在氧化铟(ITO)玻璃上采用氧化钨(WO_3)陶瓷靶沉积薄膜,研究溅射气压对WO_3薄膜结构与光学性能的影响规律,并对其电致变色行为进行了探讨。采用X射线衍射(XRD)和扫描电子显微镜(SEM)分析了WO_3薄膜的成分结构和表面形貌,紫外可见分光光度计和电化学工作站对薄膜的光调制性能、电致变色伏安特性、以及循环寿命性能进行了研究,并利用X射线光电子能谱(XPS)对WO_3薄膜在着色、褪色状态下进行了化学成分及氧化状态分析。结果表明:随着溅射气压的增大,WO3薄膜的形貌结构变得疏松、粗糙,更有利于Li+的注入与脱出,响应速度变快、调制幅度增大、电致变色性能优异,但循环寿命性能有所降低。当溅射气压为4Pa时WO3薄膜的电致变色综合性能最好,在550nm处的调制幅度可达81.0%,着色、褪色响应时间分别为7.8s、5.85s,且在1500次循环后,仍保持较高的电致变色性能。     

制备工艺对氧化钨电致变色薄膜性能的影响

采用WO3陶瓷靶,运用射频反应磁控溅射工艺,通过正交试验方法优化实验参数,制备出性能优异的WO3电致变色薄膜,通过对薄膜进行真空热处理,提高了薄膜变色存储能力。结果表明,氧分量为60%、压强为2.5Pa、功率为145W时制备的薄膜,对光调制幅度(ΔT)达89.3%。适度温度真空热处理可改善薄膜性能,着色率略有提高,变色存储时间增加(达32h),离子存储能力增大(达3.96mC/cm2),循环稳定性能良好,同时热处理使薄膜晶化,密度增加,变色响应时间增加。     

PEG改性氧化钨薄膜的电致变色特性

为改善WO₃薄膜的电致变色性能, 采用溶胶-凝胶法制备了聚乙二醇(PEG)改性的WO₃电致变色薄膜, 并对其着色态与漂白态的光学特性以及循环伏安特性进行了研究。研究表明: PEG改性的WO₃薄膜具有良好的电致变色性能, 循环5000次伏安曲线无明显衰减, 对可见光的最大透过率调制幅度可达71%。PEG的加入改变了WO₃薄膜的微结构, 形成了平均直径为9 nm的介孔, 提高了离子在其中的扩散速率, 因此改善了WO₃薄膜的电致变色性能。由于循环稳定性对于电致变色材料的实际应用至关重要, 因此这种低成本的湿化学法有望用于制备高性能的WO₃基电致变色器件。     

用脉冲电沉积法制备两类纳米介孔氧化镍电致变色薄膜的研究

采用脉冲电沉积技术在ITO导电玻璃上制备了NiO电致变色薄膜,并用X射线衍射仪、扫描电镜和能谱仪分析薄膜的结构、形貌和成份,用紫外-可见光分光光度计测试薄膜的光学性能,用循环伏安法测试薄膜的电化学性能,对比研究了Co掺杂对NiO薄膜电致变色性能的影响。结果表明Co掺杂优化了NiO薄膜表面形貌,形成了均匀分布的纳米介孔微结构,从而提高了薄膜电化学活性,同时提高了薄膜的光调制幅度。     

制备NiO电致变色薄膜的低电压反应离子镀工艺研究

采用低电压反应离子镀工艺制备NiO电致变色薄膜,重点研究不同的氧气分压对NiO薄膜的电致变色特性的影响,通过与普通电子束蒸发工艺制备的NiO薄膜进行物理性能和电致变色性能的比较,以及在塑料基板上制备NiO电致变色薄JP2 膜的讨论,总结出低电压反应离子镀技术制备NiO电致变色薄膜的工艺和优势.     

制备WO3电致变色薄膜的低压反应离子镀工艺研究

在电子束蒸发镀膜的基础上,引入低压反应离子镀工艺制备WO3电致变色薄膜,研究不同氧分压对WO3薄膜电致变色特性的影响,实验结果表明制备时选择工作气体氩气分压为2×10-2 Pa,氧分压为4×10-2 Pa时,薄膜具有最好的电致变色特性和最大的变色范围.进而采用低压反应离子镀工艺成功地实现在塑料基板上制备WO3薄膜,并对其电致变色特性进行了研究.同时对比了采用普通电子束蒸发镀膜制备的WO3薄膜的电致变色特性.     

热处理温度对TiO2薄膜结构及电色性能的影响

采用溶胶-凝胶法在镀有ITO透明电极的玻璃上制备了TiO2电致变色薄膜,用XRD、FT-IR、SEM、TG-DTA、分光光度计和电化学工作站等研究了热处理温度对其成分、结构和电致变色性能的影响.结果表明:350℃以下,薄膜呈非晶态;450℃时形成锐钛矿结构,同时出现网状分布的缝隙.薄膜具有较弱的阴极电致变色效应,对可见光的调制幅度随温度的升高而降低.当温度从120℃上升到450℃时,样品的K值由0.56升高到0.93,循环寿命由不足50次增加到10000次以上,注入电荷密度则由14.12 mC/cm2下降到6.79 mC/cm2.350℃处理的薄膜具有较好的综合性能,适于制备透射型电致变色器件的对电极.     

溶胶-凝胶-热解法制备介孔WO3薄膜及其电致变色性能研究

采用溶胶-凝胶-热解工艺,以PEG-400为结构导向模板剂,合成出介孔WO3薄膜,通过XRD、SEM、BET等对其晶相组成,显微结构,比表面积和孔径分布等进行了测试,结果表明所制备的介孔WO3薄膜材料为立方晶相,其平均孔径在6.37nm,比表面积高达20.69 m2/g;电化学循环伏安和光谱测试分析表明该薄膜具有良好的电致变色性能,对可见光具有很好的调制功能,平均最大透过率调制幅度可达69.96%.     

电致变色热控器件ITO膜层的制备与研究

针对电致变色热控器件的透明导电层开展了ITO薄膜的制备工艺研究,对薄膜制备过程中的几个主要影响因素（溅射压力、氩／氧比例、退火温度等）进行了分析,并测试了薄膜性能,制备的ITO薄膜电阻在100-120Ω／cm左右,在太阳光谱范围的吸收率小于5％,可以满足电致变色器件对透明导电层的要求。     

Electrochromic modulation of near-infrared light by WO<Subscript>3</Subscript> films deposited on silver nanowire substrates

Silver nanowire (Ag NW) transparent conductive electrodes with high conductivity and optical transmittance are fabricated. Then, WO₃ films are deposited on Ag NW electrodes by an electrochemical deposition method. The WO₃/Ag NW films act as obvious optical modulators in the visible region. More importantly, the WO₃/Ag NW films have distinct advantage on NIR modulation over conventional WO₃/ITO electrode. Meanwhile, the WO₃/Ag NW films own high electrochromic efficiency of 86.9 cm² C^?1 at NIR region of 1100 nm. Furthermore, electrochromic devices (ECDs) based on Ag NW substrates are fabricated in this study, which exhibit excellent cycling stability and distinct modulation of near-infrared light compared with ITO-based ECDs. This work is the first study that reports the application of Ag NW-based electrochromic films and electrochromic devices in modulation of NIR light. It exhibits bright prospects that the electrochromic materials deposited on Ag NW electrodes may find potential application in thermal control and emission detectors for spacecraft.     

Optimizing indium tin oxide thin films with bipolar d.c.-pulsed magnetron sputtering for electrochromic device applications

In this paper, indium tin oxide (ITO) films were prepared by bipolar d.c.-pulsed magnetron sputtering in a mixture of argon and oxygen onto unheated glass substrates. A target of ITO with 10 weight percent (wt %) tin was used. The influences of ratios of t^– _on/t⁺ _on (negative pulse-on time/positive pulse-on time) on the optical, electrical, and structural properties of ITO films have been investigated. The correlations between the deposition parameters and the film properties were discussed. An optimal condition based on reactive bipolar d.c.-pulsed sputtering for obtaining high transmittance, low resistivity, and low surface roughness of ITO films with high deposition rate is suggested. Then, ITO films grown at room temperature by bipolar d.c.-pulsed sputtering were used to form electrochromic devices of WO₃. Better electrochromic performances were found in comparison to those measured with commercially available ITO films on glass substrates.     

Size-controlled Ag nanoparticle modified WO3 composite films for adjustment of electrochromic properties

Size-controllable Ag nanoparticle ultrathin films, which were fabricated by vacuum deposition method from high purity Ag wire onto cleaned indium tin oxide conducting glass, have different color fabricated by variation of preparation conditions. The UV/Vis spectra showed that optical absorption peak of these Ag nanoparticle films can be tuned in a range from 457 nm to >650 nm. Scanning electron microscopy images showed that with increasing film thickness Ag particle size was larger. Ag/WO₃ composite films were prepared by cathodic electrodeposition of WO₃ onto the surface of Ag nanoparticle films. Spectroelectrochemistry and electrochromic properties of the resulting composite films were characterized. It was found that the electrochemical and electrochromatic properties of the composite films were adjustable with change the size of Ag nanoparticles in the composite films. Compared with a single component system of WO₃, a substantial enhancement in the electroactive and electrochromic performance for the Ag embedded WO₃ composite system was clearly observed.     

Investigations on niobium tungsten oxide thin films for optical modulation

The electrochromic parameters such as high color contrast, quick switching time, excellent modulation of percentage transmittance accompanied by long cyclic durability and stability are of utmost importance for researchers in the electrochromism. Till present, tungsten trioxide (WO₃) is the overwhelming candidate as an electrochromic material because of its excellent coloring efficiency, chemical stability and acceptable switching time. Despite, there are many possibilities to further improve the performance of tungsten oxide thin films based electrochromic devices. In this study, niobium (Nb) is doped into WO₃ lattice to further enhance its functionality and overall performance_. It is found that adding minimal concentrations of Nb (0.64%) in WO₃ results in instant coloring and bleaching times (~?11.5 and?~?2.9 s, respectively), which outwit the switching times of pristine WO₃. For Nb-doped WO₃ films, considering the percentage transmission difference between bleached and colored states, the ΔT value increased 10% from 50 to 60% at 700 nm and the maximum current density value of?~?19.4 mAcm^?2 has been achieved. In addition, an increase of 0.93 cm^?1 path length in optical density has been found that is higher than the values of 0.74 cm^?1 for only pristine WO₃ films. The corresponding current density values of the Nb-doped samples were reduced to 99.4% (16.17 mAcm^?2) and 98% (4.6 mAcm^?2), to achieve better stability and durability. Based on the band gap study, crystal structure and surface morphology of the Nb-doped samples, the electrochromic mechanism is discussed in details.

     

Characteristics of electrochromic device with polypyrrole and WO3

The characteristics of electrochromic films (WO₃, V₂O₅) prepared by sol-gel-spin coating and a vacuum evaporation process were compared to identify a new application of an electrochromic display. Polypyrrole films were prepared by electropolymerization in a pyrrole solution, acetonitrile, and TEPS (tetraethylammonium p-toluenesulfonate). The liquid electrolyte was prepared using LiClO₄, propylene carbonate, polymethylmetacrylate, and ethyl acetate. The optical modulation of the electrochromic device was measured as the LiClO₄: PMMA weight ratio changed from 10:3 to 10:5. The highest optical modulation value was when the LiClO₄: PMMA weight ratio was 10:4. Each type of film was analyzed using a four-point probe, a differential scanning calorimeter (DSC), an X-ray diffractometer (XRD), and a UV-vis spectrophotometer (DR/4000H). The ESCA spectra of the WO₃ films showed that the tungsten oxidation number decreased in a coloration state. © 2001 Kluwer Academic Publishers     

Effects of oxygen stoichiometry on electrochromic properties in amorphous tungsten oxide films

We have investigated the electrochromic properties of amorphous granular tungsten oxide (WO_3 + δ) thin films with over-stoichiometric oxygen content (δ), using LiClO₄ with propylene carbonate as an electrolyte. Different optical and electrochromic characteristics are observed with increasing δ. All the devices are electrochemically stable for more than 5000 color/bleach cycles without apparent degradation, and they have a faster response to coloration than to bleaching. WO_3 + δ films with an optimized δ value show an optical modulation of 86% at a wavelength of 630 nm and the highest coloration efficiency ever reported of ~ 213 cm²/C. The δ-dependent coloration mechanism is discussed using the site saturation model. It is proposed that WO_3 + δ films with the optimal δ value have favorable thickness and stoichiometry for the generation of Li⁺W⁺⁵ states.     

Electrochromic performance of hybrid tungsten oxide films with multiwalled-CNT additions

In this study, tungsten oxide films were prepared by sol–gel technique. Various amounts of multiwalled carbon nanotubes (MWCNTs) were added during sol–gel process to obtain hybrid WO₃/MWCNT films. The original and hybrid films were characterized by thermogravimetric analysis, X-ray diffraction analysis, and scanning electron microscopy analysis, whereas the electrochromic performance was evaluated by measuring changes in the optical transmittance caused by potentiostatic charge–discharge intercalation. The influence on the structure and properties of tungsten oxide film due to MWCNT addition was also investigated. The results showed that all of the films were amorphous and exhibited porous microstructure. The electrochromic performance of pristine WO₃ film was improved by adding MWCNTs that served as a template for the growth of WO₃ and resulted in more porous microstructure. The hybrid tungsten oxide films with 0.1 wt.% MWCNT addition exhibited the best electrochromic performance.     

Electrochromic properties of N-doped tungsten oxide thin films prepared by reactive DC-pulsed sputtering

In depositing nitrogen doped tungsten oxide thin films by using reactive DC-pulsed magnetron sputtering process, nitrous oxide gas (N₂O) was employed instead of nitrogen (N₂) as the nitrogen dopant source. The nitrogen doping effect on the structural and electrochromic properties of WO₃ thin films was investigated. X-ray diffraction (XRD) results show that the films are amorphous. Morphological images reveal that the films are characterized by a hybrid structure comprising nanoparticles embedded in amorphous matrix and open channels between the agglomerated nanoparticles, which promotes rapid charge transport through the film. Increasing the nitrogen doping concentration is found to decrease the nanoparticle size and the band gap energy. The electrochromic properties were studied using cyclic voltammetric and spectroeletrochemical techniques. The film with N content of ~ 5 at.% exhibits higher optical modulation and coloration efficiency as well as faster ion transport kinetics. The results reveal that electrochromic and lithium ion transport properties are moderately enhanced relative to the un-doped tungsten oxide thin films by appropriate content of dopant, due to the effects of nitrogen doping.     

Synthesis and characterization of WO3 thin films by surfactant assisted spray pyrolysis for electrochromic applications

Thin films of WO₃ were prepared by surfactant assisted spray pyrolysis on F-doped SnO₂ (FTO) conductive glass by using hexadecyltrimethylammonium bromide (HTAB) and polyethylene glycol (PEG400):HTAB as growth controlling agents. The surface tension of the spraying solutions was experimentally evaluated and was correlated with the deposition processes (nucleation and growth) of very smooth and homogenous films. The effect of the surfactant, alone and associated with PEG, on the structure (XRD), morphology (AFM), surface composition (XPS), FTIR and hydrophilicity (contact angle) were investigated and their influence on the electrochromic activity was discussed. Using surfactants and PEG, the coloration efficiency, transmission modulation and cycling stability of the WO₃ thin films can be enhanced.