电致变色技术从19世纪60年代发展至今, 在智能窗户、防眩目后视镜、显示器等领域的应用中取得了广泛的成功[1,2]。近几十年来, 我国电致变色技术历经从无到有的过程, 在理论研究和应用探索等多个方面都获得了重要的进展[3,4]。当前大多数电致变色器件(Electrochromic device, ECD)通常建立在玻璃等刚性基底上, 存在厚度大、共型性差、机械强度低、成本高和运输困难等不可忽视的问题。与此同时, 随着柔性和可穿戴设备在移动出行、生物医学、消费电子产品等多个应用领域的不断出现, 人们对开发廉价节能、便携灵活且能适应各种应用场景的电子设备的需求更加强烈, 迫切需要下一代电子产品在柔性、可折叠性、可穿戴性甚至可植入性方面成为可能[5]。柔性电致变色器件应运而生, 不仅成本更低, 还可以在复杂的曲面进行贴装[6], 引起了相关领域的国内外科研工作者们的广泛关注。
柔性电致变色器件指在高分子塑料等柔性基底上制备的, 在长周期的连续机械变形下仍保持高性能的, 光学性质可通过施加电场而可逆改变的电子器件。赋予电致变色器件以柔性和可拉伸性等机械特性, 可以实现自适应伪装、仿生、可穿戴显示器和变色服装等多种新型高端应用[7]。
柔性电致变色器件通常由柔性基底(Soft substrate)、透明导电电极(Transparent conductive electrode, TCE)、电致变色层(Electrochromic layer, EC layer)、离子存储层(Ion storage layer)和电解质层(Electrolyte layer)组成。按照电致变色材料类别可分为无机、有机、无机/有机复合及其他柔性电致变色器件, 常基于着色效率、光学调制范围、切换速度、寿命和循环稳定性来评估其性能。本文综述了无机、有机、无机/有机复合等柔性电致变色器件的国内外研究进展, 系统介绍了柔性器件中不同电致变色材料的优缺点, 讨论了柔性电致变色器件在性能提升和实际使用中面临的挑战, 总结并展望了柔性电致变色器件的未来发展趋势。
1 无机柔性电致变色器件
无机电致变色材料是最早进行研究的电致变色材料, 具有化学稳定性高、抗辐射性能好、易实现整个器件的全固化封装等优点[8]。无机电致变色材料主要包括金属氧化物与普鲁士蓝等, 施加电压后因其中过渡金属离子价态和浓度不同而显现出不同的颜色。在无机柔性电致变色器件的制备中, 常遇到循环次数较多后材料和基底脱离的界面故障使性能降低、电极稳定性不强、电解质漏液等问题, 因此在提高薄膜与柔性基底的附着力、保护电极、实现全固态ECD封装等方面有待探索。
1.1 金属氧化物
此类化合物种类繁多, 包括氧化态无色而还原态着色的阴极电致变色材料(如WO3、MoO3、TiO2等)以及还原态无色而氧化态着色的阳极电致变色材料(如NiO、MnO2、V2O5等), 金属氧化物在柔性基底上的沉积方法有电子束蒸镀、喷涂法、射频磁控溅射等, 可以较紧密地与柔性基底结合, 实现ECD的机械稳定性。
1.1.1 氧化钨
氧化钨具有非晶态响应速度快、多晶态对红外光调制明显的优点, 研究历史最为悠久。2015年, 何鑫等[9]结合稀酸处理和机械压印方法, 在柔性聚对苯二甲酸乙二酯(PET)基底上构建银纳米线(Ag NWs)/聚乙烯醇(PVA)复合透明电极, 引入WO3基柔性电致变色器件中, 其有与氧化铟锡(ITO)基电致变色器件相当的响应时间, 循环50次后仍可电致变色。刘星元等[10]在室温下用电子束蒸镀在PET 基底上制备集透明导电和电致变色为一体的柔性WO3/Ag/WO3薄膜, 具有优良的耐弯折性能和电致变色性能, 经过1600 次弯折, 方阻几乎没有变化。掠角沉积是制备ECD的新方法, 刘星元等[11]研究还表明蒸发掠射角75°时, WO3薄膜所具有的纳米柱结构可以释放内应力, 实现良好的耐弯折性能, 镀在PET-ITO柔性基底可得到柔性电致变色薄膜, 弯折1000次后, 变色性能无明显降低。
磁控溅射技术也可用于沉积氧化钨。2017年, Esin等[12]将WO3薄膜沉积到柔性基板上, 厚度465 nm时ECD有快速的响应时间。2017年, Oksuz等[13]将ITO或Pt和WO3薄膜层分别用作导电材料和电致变色材料, 制备了基于羊毛纺织品基材的电致变色器件, 性能符合预期。在全固态ECD方面, 2015年, 刁训刚等[14]在室温下通过磁控溅射工艺在柔性PET-ITO基底上制造了结构为ITO/NiOx/LiTaO3/ WO3/ITO的互补器件, 具有高的光学调制和着色效率。2016年, Tang等[15]将有效面积24 cm× 18 cm的ITO/WO3/Nb2O5/NiVOx/ITO全固态整体式ECD通过磁控溅射沉积在PET基板上, 可以承受8000多次循环和7.5 cm的弯曲曲率半径。Cannavale等[16]利用全氟磺酸(Nafion)膜作为固态电解质, 开发了一种室温制备全固态柔性变色器件的工艺, 着色效率高达139 cm2 ·C-1, 并且耐受1000次变色循环。
相较于以上的物理沉积技术, 溶液法成本低, 易实现掺杂和大面积制备。2017年, 刘建伟等[4]将溶剂热法制备的W18O49纳米线与Ag NWs在 PET基底上共组装得到柔性变色薄膜, 如图1所示, 在1.2 cm曲率半径下弯曲1000 次后薄膜仍具有稳定的导电性和电致变色性能。2019年, 刘向阳等[17]通过脉冲电化学沉积方法在柔性膜上制备了多孔WO3/Ag NWs/WO3膜, 三明治结构不仅保护Ag网络免受电解质的氧化和腐蚀, 还有利于电解质的渗透并减轻机械应力。2018年, 郭文熹等[18]提出了一种裂纹图案技术制造矩形Ag导电网络, 应用于WO3基柔性ECD, 具有出色的机械强度和接近于刚性ECD商业标准的光电性能。
图1
图1
溶剂热法制备的W18O49纳米线与Ag NWs在PET基底上共组装得到柔性变色薄膜[4]
Fig. 1
W18O49 nanowires and Ag NWs by solvothermal preparation co-assembled on PET substrate to obtain flexible color-changing film[4]
(a) Schematic illustration of the curved Ag and W18O49 NW film with electrochromic property; (b,c) The film attached on the curved surface of the beaker before (bleached state) and after (colored state) applying voltage; (d) In situ electrical resistance change of flexible electrochromic film after 0, 100, 200, 300, 500, and 1000 bending cycles; (e) Switching behaviors of the ECD after 0, 100, 200, 300, 400, 500, and 1000 bending cycles
1.1.2 氧化钼
1.1.3 氧化镍
1.1.4 复合及其他金属氧化物
2020年, 韩国电子部品研究院的Han等[25]通过调控最佳掺杂钨配比(x=0.024)的镍(Ni1-xWx)氧化物薄膜作为电致变色器件的对电极, 与WO3薄膜分别沉积在c-ITO(结晶态氧化铟锡)/石墨烯/PET电极, 制备了柔性器件。并在1000次脉冲电位循环中保持了稳定的40%的光学调制范围。即便在弯曲状态, 该FECD器件的颜色也会从浅黄色(-1.5 V)变为深蓝色(+1.5 V), 对机械弯曲展现良好的稳定性能。
1.2 普鲁士蓝
图2
表1 无机电致变色器件性能比较
Table 1
| Materials | Switching time/s | Coloration efficiency/(cm2·C-1) | Transmittance modulation/% | Stability/cycles | Bending radius/mm | Ref. |
|---|---|---|---|---|---|---|
| W18O49 | 10.3/7.4 | 35.7 | 60 | 1000 | 12 | [4] |
| WO3/Ag/WO3 | 11/10.5 | 136 | 53 | 3000 | 15 | [10] |
| WO3 | 3.5/8.4 | 60.1 | 73.3 | 200 | 5 | [11] |
| WO3-NiVOx | 6/5 | - | 42 | 8000 | 75 | [15] |
| WO3 | 30 | 139 | 49 | 1000 | - | [16] |
| WO3 | 9/19 | 58.95 | 89.7 | 300 | 2 | [17] |
| MoO3 | 6.2/10.9 | 34.7 | 27.7 | 150 | 11 | [19] |
| NiOx-WO3 | - | 20-35 | 60 | 125 | 36 | [22] |
| WO3-ZnO | 6.2/2.8 | 80.6 | 68.2 | - | - | [23] |
| Prussian blue -WO3 | <10 | - | 52.4 | 2250 | - | [28] |
2 有机柔性电致变色器件
有机电致变色材料的研究虽然起步稍晚, 但由于响应时间短、廉价易得、易加工、颜色变化种类丰富等优点得到了广泛研究[31]。常把有机电致变色材料分为导电聚合物、氧化-还原型、金属有机螯合物三种, 可分别通过改变掺杂程度、转换价态、能级分裂实现电致变色。在有机柔性电致变色器件的制备中同样存在不少的挑战, 如开发新的导电基底解决泄露和易燃的问题、避免电解质沉积钝化电极提高器件的长期使用性等。
2.1 导电聚合物
导电聚合物是通过掺杂获得导电性的含共轭结构的大分子, 施加电压可改变其掺杂程度及能带结构,从而改变其对入射光的吸收特征。其合成工艺简便、易加工修饰、颜色可调性强。在柔性电致变色器件方面, 此类材料不仅可用作电致变色层, 还可以胜任柔性电极, 故应用前景十分广阔。
2.1.1 聚苯胺及其衍生物
聚苯胺也是优秀的电极材料。2019年, Lu等[34]报告了在高弯曲性PANI-CNT(碳纳米管)/PET导电薄膜上电沉积PANI所得PANI/PANI-CNT/PET的性能与PANI/ITO/PET相当, 而经过100次弯曲后可以更好地保留其初始变色性能。
2018年, 汪浩等[35]采用电沉积方法, 在柔性PET-ITO基底上制备了具有改性纳米结构的柔性PANI薄膜, 获得了很好的机械柔韧性, 630 nm波长处具有80.9 cm2·C-1的高着色效率和显著的多色性能。2019年,曹亚等[36]利用PET-ITO作为透明导电基底, 喷涂单分散的SiO2/PANI核/壳纳米球用作电致变色材料, 所得柔性ECD弯曲循环500次后性能基本保持。2020年, 李垚等[37]以液体电解质负载高孔隙率的聚醚醚酮(PEEK)多孔膜作为新型电解质材料, 将聚苯胺薄膜沉积在多孔金电极上, 制备了柔性红外电致变色薄膜, 具有优异的红外发射率调节能力, 快速的开关时间(< 10 s)和良好的循环稳定性。
2.1.2 聚噻吩及其衍生物
聚噻吩及其衍生物同样具有优秀的电学性能, 例如掺杂和去掺杂时的优良稳定性、结构多样性等。近年来人们对聚-3,4-乙烯二氧噻吩(PEDOT)进行了广泛而深入的研究。2015年, 彭海琳等[38]通过连续大规模卷对卷生产石墨烯/银纳米线复合透明导电电极, 并利用PEDOT作为变色层制备出柔性ECD, 在弯曲情况下可以毫无困难地工作。
2017年, Kumar等[39]报道了涂在柔性膜上的PEDOT：PSS(聚苯乙烯磺酸盐)膜的性能经对甲苯磺酰胺-二甲基亚砜(PTSA-DMSO)处理, 可作为用于ECD应用的电极(图3), 与基于ITO电极的ECD进行比较在电化学循环和多次机械弯曲测试中均表现出更卓越的稳定性。2018年, Kim等[40]通过喷涂法制备了基于银纳米线和PEDOT：PSS的高透明导电电极, 利用EC凝胶的弹性特性, 在塑料基底上实现了柔性ECD。2017年, Chuangchote等[41]获得了透明的导电PEDOT柔性电极, 用于制造柔性电致变色器件, 聚(3-己基噻吩)用作活性层, 施加较小电压(±3 V)即从透明的浅蓝色变为紫色。
图3
2.2 氧化-还原型化合物
此类化合物常常是含共轭体系及富电子杂原子的有机小分子, 通过可逆的氧化还原过程实现电致变色,主要有联吡啶、四噻富瓦烯等及其衍生物。紫精是联吡啶的一种衍生物。2017年, Moon等[42]将二甲基二茂铁作为阳极物质掺入单庚基紫精(MHr+)和二庚基紫精(DHV2 +)凝胶中, 获得良好的着色效率, 并制备了基于凝胶橡胶特性的可显示多种颜色的可弯曲ECD。
图4
2.3 金属有机螯合物
金属离子与配体形成的有机螯合物中金属离子能级分裂, 落在可见光范围内的能级差Δ使其呈现能级差Δ的互补色, 故可作ECD中的电致变色材料使用。
2018年, 李昕等[47]将亚铁离子与三联吡啶及其衍生物配位聚合得到金属超分子聚合物FeL, 滴涂成为薄膜, 制成结构为PEN(聚萘二甲酸乙二醇酯)- ITO/FeL/Gel electrolyte/PEN-ITO的柔性ECD, 对比度41%,着色效率299.8 cm2·C-1, 着色和褪色时间为3.6 s/7.3 s, 达到了实用水平。2015年, Higuchi等[48]将具有两种颜色的金属超分子聚合物(MEPE)溶液喷墨印刷得到EC薄膜, 与固体透明薄膜电解质和透明导电薄膜层压成ECD, 在弯曲条件下仍具有30.1%的高光学对比度。2016年, Freire等[49]报道了两种聚[Ni(salen)]型电活性聚合物薄膜作为新型电致变色材料, 电沉积到ITO-PET柔性基板上, 具有良好的稳定性和光学对比度。表2列举了几种典型有机柔性电致变色器件的性能对比。
表2 有机电致变色器件性能比较
Table 2
| Materials | Switching time/s | Coloration efficiency /(cm2·C-1) | Transmittance modulation/% | Stability | Bending radius/mm | Ref. |
|---|---|---|---|---|---|---|
| PANI | 40/20 | 22.9 | 34 | 200 cycles | 6 | [34] |
| PANI | 3.9/2.61 | 80.9 | 49 | 500 cycles | 10 | [35] |
| PEDOT | 4.1/3.4 | - | 21 | 10000 cycles | 20 | [38] |
| PEDOT: PSS | 4.6/2 | 429 | 45 | 4000 cycles | - | [39] |
| ethyl viologen | 41/395 | 117.7 | 92.1 | 60000 s | 12.5 | [43] |
| monoheptyl-viologen/diheptylviologen/diphenyl-viologen | 20/34 | 87.3 | 25 | 3600 s | 10 | [44] |
| FeL | 3.6/7.3 | 299.8 | 41 | 250 cycles | - | [47] |
| MEPE | 2/26 | 445 | 40.1 | - | 10 | [48] |
| Poly[Ni(salen)]-type polymer | 157/145 | 130.4 | 88.7 | 3000 cycles | - | [49] |
3 无机/有机复合柔性电致变色器件
无机和有机电致变色材料属于优势互补的关系, 因此人们致力于研发同时包含各自优点的复合电致变色材料, 并将其应用于柔性ECD中。将金属氧化物与导电聚合物复合是很重要的一个研究方向, 常通过喷涂法等工艺实现。2016年, 王宏志等[50]在超薄PET基底上用喷涂法构建Ag NWs-W18O49 NWs网络, 并以藻酸/聚(多巴胺)复合物(Aa-PDA)和PEDOT:PSS层分别用作粘合剂和电荷平衡层, 实现了轻质、高度可弯曲和可折叠的EC膜, 可进行500次弯曲或100次折叠循环。2019年, 李丽东等[51]将PANI和WO2.7 NWs复合获得电致变色电极, 喷涂金纳米粒子提高导电性, 并合成新型自愈合水凝胶作为固体电解质, 组装了具有电致变色和自修复特性的柔性超级电容器。
2016年, Lee等[52]在银栅格/ PEDOT：PSS杂化膜上涂覆一层WO3纳米颗粒制备ECD, 在633 nm处有81.9%的光学调制, 优秀的响应速度和着色效率, 更获得了出色的电化学循环稳定性和机械柔韧性。如图5所示, 在1200次弯曲循环后, 光调制仅有7.5%的衰减。2017年, 赵九蓬等[53]制作了新型WO3·2H2O/PEDOT膜, 由瞬态加热方法牢固地固定在使用Ag作为导电层的EVA(乙烯-醋酸乙烯共聚物)/PET电极上, 该电致变色膜机械坚固, 可以扭曲, 折叠和褶皱, 而不会降低性能, 且与WO3·2H2O膜相比实现了更高的性能。2016年, Vinuales等[54]报道基于仅在120 ℃进行热处理的紫精改性TiO2纳米结构薄膜的柔性塑料电致变色器件, 还报道了与塑料基材相容性更优的紫精的合成, 最后展示了大面积全固态设备(40 cm×30 cm), 证明该技术适用于生产大面积塑料ECD。2018年, Kang等[55]设计了一种高性能超柔性新型混合透明电极(AgNWS/ PEDOT:PSS), 以低温合成Ni(OH)2和聚乙烯亚胺聚氧乙烯醚(PEIE)复合材料为电致变色层, 用于制备双功能电致变色-超级电容器件。该FECD器件在10000次充放电循环下表现出稳定的循环稳定性, 在633 nm处的着色效率高达517 cm2·C-1, 开关速度快(<0.6 s)。此外, 在弯曲半径为1 mm的情况下,即使在8000次弯曲循环后, 电容保持率仍达到90%, 并且可以容忍15次褶皱而没有明显的退化,保持优异的机械坚固性和灵活性。表3列举了几种典型无机/有机复合柔性电致变色器件的性能对比。
图5
表3 无机/有机复合电致变色器件性能比较
Table 3
| Materials | Switching time/s | Coloration efficiency /(cm2·C-1) | Transmittance modulation/% | Stability/cycles | Bending radius/mm | Ref. |
|---|---|---|---|---|---|---|
| W18O49 NWs-PEDOT:PSS | 18.2/6.6 | 118.1 | 34.3 | - | 2.5 | [50] |
| PEDOT:PSS-WO3 | 1.9/2.8 | 124.5 | 81.9 | 2000 | 20 | [52] |
| WO3·2H2O-PEDOT | 4.4/2.6 | 180.2 | 63.1 | - | - | [53] |
| Viologen-TiO2 | 8/6 | 226 | 53 | 1000 | - | [54] |
| Ag NW/Ni(OH)2-PEIE/PEDOT:PSS | 0.3/0.6 | 517 | 30 | 100 | 1 | [55] |
4 其他材料柔性电致变色器件
近年来, 新型(柔性)电致变色器件中不断涌现出新材料, 如微孔金属-有机框架(Microporous metal-organic frameworks)[56,57]、有机-卤化物杂化钙钛矿(Organic-halide hybrid perovskites)[58]、二维过渡金属碳/氮化物(MXenes)[59]等, 极大地扩充了电致变色材料的选择范围。例如, 2019年Tan等[60]展示了使用Guest@MOF概念来设计电致变色薄膜, DHTP@Zn-MOF-74的薄膜在柔性 PET-ITO基底上生长,可在无色和品红色之间可逆切换, 为发现具有可调节特性的新Guest@MOF电致变色系统打开大门。
5 可拉伸电致变色器件
从技术上说, 赋予刚性电致变色器件可拉伸性比可弯曲性更难实现, 人们不断将电致变色器件顺着刚性、柔性、可拉伸性的发展趋势推进, 在可拉伸ECD方面也取得了丰硕的成果。可拉伸电致变色器件要求在各种长周期的机械变形(弯曲、折叠和拉伸)下仍保持高性能, 研发主要集中在平衡导电性、光学透明度和机械拉伸性的重大挑战上。
图6
图7
可拉伸ECD应用前景广阔。2019年, Ha等[67]报告了基于聚(3-甲基噻吩)和普鲁士蓝电极的可拉伸ECD, 显示出在弯曲和30%双轴拉伸下的机械稳定性。2019年, 陈花玲等[68]通过整合可拉伸光子晶体和形状记忆合金复合材料获得可拉伸电致变色器件, 在1.0~1.5 V的电压下, 可以在整个可见光范围内实现变色, 具有驱动电压低、柔顺性好、变色范围宽、响应时间短和有效变色面积大的特点, 而且有优异的软动态显示和伪装功能, 高抗冲击性能。2018年, 贾春阳等[69]展示了一种具有仿生特性的共聚物薄膜, 该薄膜同时整合了电致变色三苯胺和自我修复的Diels Alder基团, 柔性和可拉伸的共聚物薄膜的作用就像自然变色龙皮肤, 其表现出显著的颜色变化, 并且还具有优异的自愈性能。表4列举了几种典型可拉伸电致变色器件的性能对比。
表4 拉伸电致变色器件性能比较
Table 4
| Materials | Switching time/s | Coloration efficiency /(cm2·C-1) | Transmittance modulation/% | Stability | Bending radius/mm | Ref. |
|---|---|---|---|---|---|---|
| WO3/Ag/PEDOT:PSS/WO3 | 1.82/0.75 | - | 23 | 30000 s | 5 | [61] |
| Heptyl Viologen | 32/43 | 31.82 | 74.5 | 100 cycles | 4.8 | [63] |
| WO3 nanotube / PEDOT: PSS | <10 | 83.9 | 37.7 | 20000 cycles | 40 | [65] |
| WO3-PANI | 4.1/2.1 | 75.5 | 40 | 500 cycles | 5 | [66] |
| poly(3-methylthiophene)/Prussian blue | 1.3/1.2 | 201.6 | 17.8 | 180 cycles | 2.5 | [67] |
| copolymer DFTPA-PI-MA | 5.3/12.2 | 82.2 | 60 | 100 cycles | - | [69] |
6 面临的挑战和发展方向
近年来, 虽然柔性电致变色器件已经获得了较多的研究, 但是在器件结构、器件性能及应用方面仍然存在许多亟待解决的问题, 有很大的发展空间。下面整合了目前柔性电致变色器件中存在的问题和挑战, 并展望了下一步研究中的可行方案。
6.1 器件性能
6.1.1 电致变色性能
6.1.2 机械稳定性
在多次弯折后, 不少柔性ECD的电致变色性能衰减严重, 如光学调制率和循环稳定性。可能是因为材料和基底产生一定程度的脱离, 界面故障造成了薄膜性能的降低, 因此需要开发新型材料和改良制备技术使材料与基底紧密结合, 提高ECD的性能。此外, 要实现高性能可拉伸ECD, 除了电致变色材料, 开发新的弹性基底和耐腐蚀的可拉伸透明电极也十分重要。
6.2 实际应用面临的挑战
6.2.1 全固态化
6.2.2 大面积生产
受实验室制备技术的规模限制, 制备出的样品不仅面积不够大, 而且难以实现均匀性, 限制了柔性电致变色器件应用的发展。器件的大面积制备需要考虑卷对卷等大规模生产方式。要控制各个功能层的均匀涂覆, 可考虑对柔性基底表面进行物理或者化学改性, 不仅有利于降低薄膜沉积缺陷, 还有利于提高膜基附着力。
6.2.3 成本问题
受活性材料、封装材料和制备技术的限制, 目前柔性ECD有较高的商业化成本和有限的应用范围。一种前景广阔的方式是采用化学液相合成结合微电子打印技术、雾化沉积技术、流延法等制备复合柔性电致变色薄膜, 不仅成本低廉、光学调制范围好, 且制备过程无需高真空环境、节约能源。但是先合成、后涂覆的策略所得薄膜往往在基底上的附着力逊色于物理沉积得到的薄膜, 后续需要对材料及成膜技术进行改进。
6.2.4 多功能化
通过集成电致变色、光致变色、电致动、光电探测、电化学储能等各种功能模式, 实现单一器件的多功能化是下一代电子器件发展的重要方向, 目前柔性电致变色器件在这一方面的研究较少, 需要不断探索前进。
7 结束语
随着各种器件结构、加工技术和新型材料的发展, 基于其共型性好、机械强度高、成本低的优势, 柔性电致变色器件具有广阔的应用前景。本文分类讨论了基于不同变色材料制备的柔性电致变色器件的研究现状, 重点评述了可拉伸电致变色器件的最新进展。然而, 柔性电致变色器件的研发当前仍然处于初级阶段, 在开发新型大面积柔性导电基底、制备柔性电致变色薄膜、封装柔性电致变色器件等方面尚有较大的发展空间。除了提高器件本身的电致变色性能和机械稳定性, 器件在实际应用中也面临延长使用寿命等巨大的挑战。此外, 柔性电致变色器件在全固态、大面积、低成本和多功能化等方面将成为今后的研究重点。国外学者的研究主要集中于提升电致变色层性能、开发提高基底附着力新技术等领域。国内学者则致力于改进衬底、导电层和电致变色层等组成部分, 匹配各层之间的应力关系, 力求实现器件的柔性化、轻便化, 相较而言, 在关键制备技术突破、科研与市场结合等方面与国外仍存在不小的差距。总之, 柔性电致变色器件拥有巨大潜力与可能性, 势必引领下一代电子技术革命。
参考文献
Highly efficient, near-infrared and visible-light modulated electrochromic devices based on polyoxometalates and W18O49 nanowires
Multifunctional hydrogel enables extremely simplified electrochromic devices for smart windows and ionic writing boards
Advances in inorganic all-solid-state electrochromic materials and devices
Large area co-assembly of nanowires for flexible transparent smart windows
LACOUR STÉPHANIE P,
et al.Materials chemistry in flexible electronics
Electrochromic metal oxides: recent progress and prospect
Recent advances in flexible electrochromic devices: the prerequisites, challenges and prospects
Inorganic electrochromic materials based on tungsten oxide and nickel oxide nanostructures
Pretreatment optimization of silver nanowire based transparent electrode and its application in flexible electrochromic devices
High-performance ITO-free electrochromic films based on bi-functional stacked WO3/Ag/WO3 structures
Dual-functional WO3 nanocolumns with broadband antireflective and high-performance flexible electrochromic properties
The three-dimensional, high-porous, and oriented WO3 nanocolumn film with broadband antireflective and high-performance flexible electrochromic dual-functionalities is achieved by utilizing a simple, one-step, room-temperature glancing angle deposition without any catalysts and templates. It is found that the WO3 nanocolumn film is effective in increasing the optical transparency in the visible range, enhancing the color-switching response time as well as improving the mechanical flexibility and electrochemical cycling stability in comparison to dense WO3 film. The further optical, morphological, and electrode reaction kinetics analyses reveal that these improvements can be attributed to its unique porous nanocolumn arrays, which reduce the refractive index, facilitate the interfacial charge-transfer and ion-penetration, and alleviate the internal stress of the film under the bending treatment. These results would provide a simple and effective guidance to design and construct low-cost, robust, flexible, stable, and transparent electrochromic smart windows.
Electrochromic characteristics of radio frequency plasma sputtered WO3 thin films onto flexible polyethylene terephthalate substrates
RF sputtered electrochromic wool textile in different liquid media
An all-thin-film inorganic electrochromic device monolithically fabricated on flexible PET/ITO substrate by magnetron sputtering
Large-area flexible monolithic ITO/WO3/Nb2O5/NiVOx/ITO electrochromic devices prepared by using magnetron sputter deposition
Room temperature processing for solid-state electrochromic devices on single substrate: from glass to flexible plastic
Pulsed electrochemical deposition of porous WO3 on silver networks for highly flexible electrochromic devices
Controllable and large-scale fabrication of flexible ITO-free electrochromic devices by crackle pattern technology
Highly stable and flexible ITO- free electrochromic films with bi-functional stacked MoO3/Ag/MoO3 structures
Equipment-free deposition of graphene-based molybdenum oxide nanohybrid Langmuir Blodgett films for flexible electrochromic panel application
Investigation of electrodeposited NiO films as electrochromic material for counter electrodes in smart windows
Electrochromic properties and performance of NiOx films and their corresponding all-thin-film flexible devices prepared by reactive DC magnetron sputtering
Bi-functional flexible electrodes based on tungsten trioxide/zinc oxide nanocomposites for electrochromic and energy storage applications
Template-free mesoporous electrochromic films on flexible substrates from tungsten oxide nanorods
Investigation of all-solid-state electrochromic devices with durability enhanced tungsten-doped nickel oxide as a counter electrode
Crack-free 2D-inverse opal anatase TiO2 films on rigid and flexible transparent conducting substrates: low temperature large area fabrication and electrochromic properties
Flexible electrochromic V2O5 thin films with ultrahigh coloration efficiency on graphene electrodes
Synthesis of poly(methyl methacrylate)-succinonitrile composite polymer electrolyte and its application for flexible electrochromic devices
Point-of-care diagnoses: flexible patterning technique for self-powered wearable sensors
This paper demonstrated the fabrication of a facile, low-cost, and self-powered platform for point-of-care fitness level and athletic performance monitoring sensor using electrochemical lithography method and its application in body fluid sensing. Flexible Au/prussian blue electrode was employed as the indicating electrode, where the color change was an indication of fitness level and athletic performance. A piece of Al foil, Au/multiwalled carbon nanotubes (MWCNTs)-glucose dehydrogenase, and Au/polymethylene blue-MWCNTs-lactic dehydrogenase electrodes were used for the detection of ionic strength, glucose, and lactic acid in sweat, respectively, which allows the sensor to work without any extra instrumentation and the output signal can be recognized by the naked eyes. The advantages of these sensors are (1) self-powered; (2) readily applicable to the detection of any electroactive substance by an electrochromic material; (3) easy to fabricate via two steps of EDP; and (4) point-of-care. By assembling the energy and sensing components together through a transparent adhesive tape, the proposed self-powered wearable biosensor exhibits superior performances, indicating its broad applied prospect in the point-of-care diagnoses.
Visualized UV photodetectors based on prussian blue/TiO2 for smart irradiation monitoring application
New roll-to-roll processable PEDOT-based polymer with colorless bleached state for flexible electrochromic devices
Development and characterization of a flexible electrochromic device based on polyaniline and enzymatically synthesized poly (gallic acid)
A wearable second skin-like multifunctional supercapacitor with vertical gold nanowires and electrochromic polyaniline
A highly bendable transparent electrode for organic electrochromic devices
Polyaniline films with modified nanostructure for bifunctional flexible multicolor electrochromic and supercapacitor applications
Patterned flexible electrochromic device based on monodisperse silica/polyaniline core/shell nanospheres
Highly-conductive porous poly(ether ether ketone) electrolyte membranes for flexible electrochromic devices with variable infrared emittance
Roll-to-roll encapsulation of metal nanowires between graphene and plastic substrate for high-performance flexible transparent electrodes
Transparent conductive film on plastic substrate is a critical component in low-cost, flexible, and lightweight optoelectronics. Industrial-scale manufacturing of high-performance transparent conductive flexible plastic is needed to enable wide-ranging applications. Here, we demonstrate a continuous roll-to-roll (R2R) production of transparent conductive flexible plastic based on a metal nanowire network fully encapsulated between graphene monolayer and plastic substrate. Large-area graphene film grown on Cu foil via a R2R chemical vapor deposition process was hot-laminated onto nanowires precoated EVA/PET film, followed by a R2R electrochemical delamination that preserves the Cu foil for reuse. The encapsulated structure minimized the resistance of both wire-to-wire junctions and graphene grain boundaries and strengthened adhesion of nanowires and graphene to plastic substrate, resulting in superior optoelectronic properties (sheet resistance of approximately 8 Omega sq(-1) at 94% transmittance), remarkable corrosion resistance, and excellent mechanical flexibility. With these advantages, long-cycle life flexible electrochromic devices are demonstrated, showing up to 10000 cycles.
ITO-free solution- processed flexible electrochromic devices based on PEDOT: PSS as transparent conducting electrode
Electrochromic devices (ECDs) are emerging as novel technology for various applications ranging from commercialized smart window glasses, goggles, and autodimming rear view mirrors to uncommon yet more sophisticated applications such as infrared camouflage in military and thermal control in space satellites. The development of low-power, lightweight, inexpensive, and flexible devices is the need of the hour. In this respect, utilizing PEDOT:PSS as transparent conducting electrode (TCE) to replace indium tin oxide (ITO) and metal based TCEs for ECDs is a promising solution for the aforementioned requirements. In this work we have demonstrated the performance of PEDOT:PSS films coated on flexible substrates, treated with PTSA-DMSO, as TCEs for ECD applications and their comparison with that of ITO based ECDs. The PEDOT:PSS based flexible TCEs used in this study have conductivity of 1400-1500 S.cm(-1) and figure of merit (FoM) of 70-77. The process of increasing the conductivity of PEDOT:PSS films also led to the broadening of the conducting potential window (CPW), which is important for electrochemical applications of PEDOT:PSS when used as a stand-alone electrode. More than achieving a comparable electrochromic contrast, switching time, and coloration efficiency with respect to the ITO based ECDs, PEDOT:PSS devices also had the added advantage of good mechanical flexibility. These devices demonstrated superior stability during electrochemical cycling and multiple mechanical bending tests, making them an inexpensive alternative to the costly ITO based ECD technology.
Spray-coated transparent hybrid electrodes for high-performance electrochromic devices on plastic
PEDOT: PSS nanofilms fabricated by a nonconventional coating method for uses as transparent conducting electrodes in flexible electrochromic devices
Voltage-tunable multicolor, sub-1.5 V, flexible electrochromic devices based on ion gels
Mechanically robust, highly ionic conductive gels based on random copolymers for bending durable electrochemical devices
Flexible and transparent electrochromic displays with simultaneously implementable subpixelated ion gel-based viologens by multiple patterning
Incorporating paper matrix into flexible devices based on liquid electrochromic mixtures: enhanced robustness, durability and multi- color versatility
Solution processable, electrochromic ion gels for sub-1 V, flexible displays on plastic
Preparation and stability of flexible electrochromic devices based on metal supramolecular polymers
Printed multicolor high-contrast electrochromic devices
In this study, electrochemical responses of inkjet-printed multicolored electrochromic devices (ECD) were studied to evaluate the feasibility of presenting multiple colors in one ECD. Metallo-supramolecular polymers (MEPE) solutions with two primary colors were inkjet-printed on flexible electrodes. By digitally controlling print dosages of each species, the colors of the printed EC thin film patterns can be adjusted directly without premixing or synthesizing new materials. The printed EC thin films were then laminated with a solid transparent thin film electrolyte and a transparent conductive thin film to form an ECD. After applying a dc voltage, the printed ECDs exhibited great contrast with a transmittance change (DeltaT) of 40.1% and a high coloration efficiency of 445 cm(2) C(-1) within a short darkening time of 2 s. The flexible ECDs also showed the same darkening time of 2 s and still had a high DeltaT of 30.1% under bending condition. This study demonstrated the feasibility to fabricate display devices with different color setups by an all-solution process and can be further extended to other types of displays.
High performance electrochromic devices based on poly[Ni(salen)]-type polymer films
We report the application of two poly[Ni(salen)]-type electroactive polymer films as new electrochromic materials. The two films, poly[Ni(3-Mesalen)] (poly[1]) and poly[Ni(3-MesaltMe)] (poly[2]), were successfully electrodeposited onto ITO/PET flexible substrates, and their voltammetric characterization revealed that poly[1] showed similar redox profiles in LiClO4/CH3CN and LiClO4/propylene carbonate (PC), while poly[2] showed solvent-dependent electrochemical responses. Both films showed multielectrochromic behavior, exhibiting yellow, green, and russet colors according to their oxidation state, and promising electrochromic properties with high electrochemical stability in LiClO4/PC supporting electrolyte. In particular, poly[1] exhibited a very good electrochemical stability, changing color between yellow and green (lambda = 750 nm) during 9000 redox cycles, with a charge loss of 34.3%, an optical contrast of DeltaT = 26.2%, and an optical density of DeltaOD = 0.49, with a coloration efficiency of eta = 75.55 cm(2) C(-1). On the other hand, poly[2] showed good optical contrast for the color change from green to russet (DeltaT = 58.5%), although with moderate electrochemical stability. Finally, poly[1] was used to fabricate a solid-state electrochromic device using lateral configuration with two figures of merit: a simple shape (typology 1) and a butterfly shape (typology 2); typology 1 showed the best performance with optical contrast DeltaT = 88.7% (at lambda = 750 nm), coloration efficiency eta = 130.4 cm(2) C(-1), and charge loss of 37.0% upon 3000 redox cycles.
Light weight, highly bendable and foldable electrochromic films based on all-solution- processed bilayer nanowire networks
An electrochromic and self- healing multi-functional supercapacitor based on PANI/nw-WO2.7/ Au NPs electrode and hydrogel electrolyte
Highly stable transparent conductive silver grid/PEDOT: PSS electrodes for integrated bifunctional flexible electrochromic supercapacitors
Highly robust and flexible WO3·2H2O/PEDOT films for improved electrochromic performance in near-infrared region
Plastic electrochromic devices based on viologen-modified TiO2 films prepared at low temperature
A novel design of hybrid transparent electrodes for high performance and ultra-flexible bifunctional electrochromic-supercapacitors
Facile deposition of multicolored electrochromic metal-organic framework thin films
Double-sided electrochromic device based on metal-organic frameworks
Devices displaying controllably tunable optical properties through an applied voltage are attractive for smart glass, mirrors, and displays. Electrochromic material development aims to decrease power consumption while increasing the variety of attainable colors, their brilliance, and their longevity. We report the first electrochromic device constructed from metal organic frameworks (MOFs). Two MOF films, HKUST-1 and ZnMOF-74, are assembled so that the oxidation of one corresponds to the reduction of the other, allowing the two sides of the device to simultaneously change color. These MOF films exhibit cycling stability unrivaled by other MOFs and a significant optical contrast in a lithium-based electrolyte. HKUST-1 reversibly changed from bright blue to light blue and ZnMOF-74 from yellow to brown. The electrochromic device associates the two MOF films via a PMMA-lithium based electrolyte membrane. The color-switching of these MOFs does not arise from an organic-linker redox reaction, signaling unexplored possibilities for electrochromic MOF-based materials.
Electrochemical doping of halide perovskites with ion intercalation
Halide perovskites have recently been investigated for various solution-processed optoelectronic devices. The majority of studies have focused on using intrinsic halide perovskites, and the intentional incoporation of dopants has not been well explored. In this work, we discovered that small alkali ions, including lithium and sodium ions, could be electrochemically intercalated into a variety of halide and pseudohalide perovskites. The ion intercalation caused a lattice expansion of the perovskite crystals and resulted in an n-type doping of the perovskites. Such electrochemical doping improved the conductivity and changed the color of the perovskites, leading to an electrochromism with more than 40% reduction of transmittance in the 450-850 nm wavelength range. The doped perovskites exhibited improved electron injection efficiency into the pristine perovskite crystals, resulting in bright light-emitting diodes with a low turn-on voltage.
Electrochromic effect in titanium carbide MXene thin films produced by dip-coating
Electrochromic thin films of Zn-based MOF-74 nanocrystals facilely grown on flexible conducting substrates at room temperature
Ultraflexible, stretchable and fast- switching electrochromic devices with enhanced cycling stability
Novel stretchable ambipolar electrochromic devices based on highly transparent AgNW/PDMS hybrid electrodes
Highly transparent AgNW/PDMS stretchable electrodes for elastomeric electrochromic devices
Flexible electrochromic materials based on CNT/PDA hybrids
Materials that change color in response to external stimuli can cater to diverse applications from sensing to art. If made flexible, stretchable and weavable, they may even be directly integrated with advanced technologies such as smart textiles. A new class of engineered composite based on polydiacetylene (PDA) functionalized carbon nanotubes (CNT) shows tremendous potential in this regard. While the inherent multi stimuli chromatic response of the polymer (blue to red) is retained, the underlying conducting CNTs invoke electrochromism in PDA. Further, the fiber form factor of dry-spun CNT yarns facilitate direct weaving of large scale electrochromic fabrics, where current flow and thus color change can be accurately controlled. This review summarizes the fundamental aspects of CNT yarns and PDAs, focusing especially on their interaction chemistry which results in the scientifically and commercially appealing electrochromic transition in these hybrids.
All-transparent stretchable electrochromic supercapacitor wearable patch device
Flexible and stretchable electrochromic supercapacitor systems are widely considered as promising multifunctional energy storage devices that eliminate the need for an external power source. Nevertheless, the performance of conventional designs deteriorates significantly as a result of electrode/electrolyte exposure to atmosphere as well as mechanical deformations for the case of flexible systems. In this study, we suggest an all-transparent stretchable electrochromic supercapacitor device with ultrastable performance, which consists of Au/Ag core-shell nanowire-embedded polydimethylsiloxane (PDMS), bistacked WO3 nanotube/PEDOT:PSS, and polyacrylamide (PAAm)-based hydrogel electrolyte. Au/Ag core-shell nanowire-embedded PDMS integrated with PAAm-based hydrogel electrolyte prevents Ag oxidation and dehydration while maintaining ionic and electrical conductivity at high voltage even after 16 days of exposure to ambient conditions and under application of mechanical strains in both tensile and bending conditions. WO3 nanotube/PEDOT:PSS bistacked active materials maintain high electrochemical-electrochromic performance even under mechanical deformations. Maximum specific capacitance of 471.0 F g(-1) was obtained with a 92.9% capacity retention even after 50000 charge-discharge cycles. In addition, high coloration efficiency of 83.9 cm(2) C(-1) was shown to be due to the dual coloration and pseudocapacitor characteristics of the WO3 nanotube and PEDOT:PSS thin layer.
Inkjet-printed metal oxide nanoparticles on elastomer for strain-adaptive transmissive electrochromic energy storage systems
Low power stretchable active-matrix red, green, blue (RGB) electrochromic device array of poly(3-methylthiophene)/Prussian blue
Stretchable electrochromic devices enabled via shape memory alloy composites (SMAC) for dynamic camouflage
Intelligent biomimetic chameleon skin with excellent self-healing and electrochromic properties
Animals such as chameleons possess a natural ability to adjust their skin color as a preventive measure to deter any potential threat and to self-heal damaged skin tissues. Inspired by this, we present here a copolymer film possessing biomimetic properties that simultaneously integrates electrochromic triphenylamine and self-healing Diels-Alder groups. The flexible and stretchable copolymer film acts like natural chameleon skin, which exhibits significant color variation and also possesses excellent self-healing properties. These remarkable features make it a promising material for overcoming the crack-generation issue inherited by conventional biomimetic chameleon skin. Moreover, a flexible and wearable skin device based on the copolymer film with silver fabric as a electrode has also been fabricated. The electrochromic and self-healing properties were verified for the copolymer film, and it has been elucidated that the intelligent biomimetic
The state-of-the-art flexible electrochromic material
