silver nanowires stacking composite films for high-performance electrochromic devices

Solar Energy Materials and Solar Cells 200 (2019) 109919

Contents lists available at ScienceDirect

Solar Energy Materials and Solar Cells journal homepage: www.elsevier.com/locate/solmat

Conducting polymer/silver nanowires stacking composite films for highperformance electrochromic devices

T

Wenzhi Zhanga,∗, Xianghong Chena, Ge Zhanga, Sumin Wanga, Shengbo Zhua, Xinming Wua, Yan Wanga, Qiguan Wanga, Chenglong Hub a

Key Laboratory for Photoelectric Functional Materials and Devices of Shaanxi Province, School of Materials and Chemical Engineering, Xi’ an Technological University, Xi’ an 710021, China b Key Laboratory of Optoelectronic Chemical Materials and Devices of Ministry of Education, School of Chemistry and Environmental Engineering, Jianghan University, Wuhan 430056, China

A R T I C LE I N FO

A B S T R A C T

Keywords: Electrochromic polymer Silver nanowires Nanocomposite Optical contrast Electrochromic device

Conducting polymers (CPs) are promising candidates for next-generation electrochromic (EC) materials due to their excellent processability, flexibility, multicolor changes, easy design, low cost and low operation potential. However, the relatively low optical contrast, slow switching speed, and poor cycling performance hinder their practical applications for more than forty years. Here, electrochromic polymer (ECP)/silver nanowires (AgNWs) stacking composite films on indium tin oxide (ITO) coated glass are built as electrodes to facilitate the diffusion and migration of ions in electrochromic devices (ECDs). Notably, the presence of AgNWs network plays a critical role to improve electrical conductivity, benefit ions doping and dedoping, increase surface area, and reduce applied potential. As a result, the EC performance of ECP/AgNWs nanocomposite device is significantly improved, which exhibits a highly optical contrast, short response time, and stable cycling. This study suggests that rational design of stacking nanocomposite micromorphology on electrode level might be a useful strategy for fabricating high performance ECDs.

1. Introduction Electrochromism is defined as a reversible optical absorbance/ transmittance change upon application of a modest driving potential. EC materials as new functional materials of green environmental protection, energy saving and low carbon, are considered one of the most promising smart materials, which can be applied in displays [1,2], EC windows [3–6], sensors [7], tags [8], antiglare rearview mirrors, electronic books, protective eyewear [9] and adaptive camouflage [10–13]. The earliest studied EC materials are transition metal oxides, such as tungsten oxide (WO3) and iridium dioxide (IrO2), which suffer from long response time, high cost and high oxidative potential. With the continuing development of organic compounds, conducting polymers have become a potential candidate for next-generation EC materials owing to their excellent processability, flexibility, multicolor changes, easy design, low cost and low operation potential [14–17]. However, the relatively low optical contrast, slow switching speed, and poor cycling performance limit the practical applications of electrochromic polymers. So far, there are three ways to improve the optical contrast, switching speed, and cycling performance of ECPs. One is to carry out

∗

the molecular design and structural modification of ECPs, by introducing donor-acceptor conjugated structures or hybrid π-conjugated systems or functional groups, copolymerization, color mixing of ECPs, chemical oxidation or surface pre-treatment of polymer electrodes [18–27]. Cao et al. synthesized the ECPs with repeat units composed of electron-rich dimethoxyphenylene in alternation with dimers of 3,4dialkoxy- and 3,4-propylenedioxythiophenes, which exhibited improved redox stability and higher optical contrast [28]. Österholm et al. fabricated the user-controlled, high-contrast, fast-switching, and fully solution-processable electrochromic lenses by simple predictive color mixing of ECPs. The lens achieved highly transmissive colored and colorless states with fast switching in a window and 45% change in transmittance upon a full switch [9]. Ouyang et al. disclosed that the incorporation of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) ionic liquid with the conducting polymer film could shorten the switching time and increase its durability significantly [29]. Pittelli et al. demonstrated that the phosphonic acid surface pre-treatment and chemical oxidation of polymer electrodes enhanced the optical contrast and stability of ECD [30]. Although the molecular design and structural modification of ECPs can improve the performance of EC

Corresponding author. E-mail address: [email protected] (W. Zhang).

https://doi.org/10.1016/j.solmat.2019.109919 Received 22 November 2018; Received in revised form 24 April 2019; Accepted 30 April 2019 0927-0248/ © 2019 Elsevier B.V. All rights reserved.

Solar Energy Materials and Solar Cells 200 (2019) 109919

W. Zhang, et al.

2. Experimental section

materials, we have to devise the synthetic routes. The synthetic process is complicated and its cost is high, which restricts application of these materials in ECDs. Another way is to generate the porous structure within the polymer films and tune the morphology of ECPs, by washing salts out, thermal nanoimprint lithography, nanostructure templates, organic templates or designing soft cross-linked networks [31–34]. Pan et al. prepared the electroactive triphenylamine-based polyamide films with porous structure by washing out tetrabutylammonium tetrafluoroborate (TBABF4), which efficiently improved the driven potential and response time of ECDs [35]. Neo et al. utilized a thermal nanoimprinting method to create periodic nanostructures on the conjugated polymer films, and the corresponding ECDs exhibited the superior performances in optical contrast, switching speeds and coloration efficiency compared to the non-nanostructured counterpart [36]. Qin et al. prepared the nano-soft network of poly(3,4-dioxythiophene) dimer (PM-BTE), possessing excellent electrochromic properties such as low switching voltage, short response time, and outstanding stability [37]. However, these methods need to design and synthesize the ECPs, nanostructure templates or utilize special instruments and techniques, including complex process and cumbersome operation. This may lead to poor operability of their application. The third approach is to construct polymer-based EC nanocomposites by incorporating nanoparticles, nanotubes, nanocages, nanosheets, nanoslit arrays, nanorods or nanowhiskers into polymer matrix [38–42]. Nunes et al. prepared a TiO2@poly[Ni(salen)] nanocomposite in the presence of TiO2 nanoparticles, showing excellent electrochemical stability and an enhancement of 16.7% in optical modulation [43]. Hu et al. fabricated the novel halloysite/polyaniline nanocomposites by in-situ chemical polymerization. The nanocomposites films possessed higher optical contrast, faster response time, and more remarkable switching stability in comparison to the pure polyaniline [44]. Shi et al. prepared the poly(3,4-ethylenedioxythiophene)/graphene oxide hybrid nanostructures by an in situ electro-polymerization process. The optical contrast of hybrid nanostructure increased from 23.4% to 31.4%, and its response time was shortened [45]. Zhou et al. prepared the polyaniline/manganese dioxide (PANI/MnO2) hybrid electrochromic films through one-pot potentiostatically anodic electrodeposition process. Compared with neat PANI film, the hybrid film showed much higher optical contrast, coloration efficiency, and cycling stability [46]. Recently, Zhang et al. reported a kind of rodlike nanocellulose/polyaniline nanocomposites with core-shell structure, exhibiting fast response time, high optical contrast and remarkable switching stability [47]. The above-described methods for fabricate the nanocomposites are facile and efficient. However, the nanomaterials used are either nonconductive or conductive nanosheets or nanotubes. To the best of our knowledge, there are yet no reports on the use of ECP/conductive nanowires composite films for EC applications. AgNWs possess optoelectronic advantages with low-cost manufacturing, high conductivity and optical transmittance, and have been proposed for applications in transparent or stretchable functional devices [48,49]. Herein, we develop a simple and effective fabrication of ECP coated AgNWs nanocomposite (ECP/AgNWs) electrode based on ITO substrate for the first time. The transparent conductive film of AgNWs was prepared by rod-coating the AgNWs dispersion on the surface of ITO conductive glass. Then, the ECP/AgNWs/ITO nanocomposite electrodes were obtained by electrochemical polymerization. To investigate the influence of AgNWs on the electrochromic properties of polymer, the ECP/AgNWs/ITO electrodes were further assembled into the ECDs. The ECDs based on nanocomposite films demonstrated improved electrochromic and electrochemical properties. This approach can be easily scaled up and be extended to prepare the high-performance polymerbased EC nanocomposites.

2.1. Materials ITO glass was received from Zhuhai Kaivo Optoelectronic Technology Co., Ltd (China), its sheet resistance was 7.9–8.5 Ω/□, and the thickness of ITO film on glass substrate was 188–191 nm. Silver nitrate (AgNO3), lithium perchlorate (LiClO4), thiophene, 3-thiopheneethanol and 3-thiopheneboronic acid were obtained from Acros Organics. Polyvinylpyrrolidone (MW = 55000 g/mol, PVP-55000), PVP (MW = 360000 g/mol, PVP-360000), propylene carbonate, acetonitrile and boron trifluoride etherate were purchased from Alfa-Aesar company. Ethylene glycol (EG) and sodium chloride (NaCl) were supplied by Sinopharm Chemical Reagent Co., Ltd (China). Poly (methyl methacrylate) (MW = 350000 g/mol) was obtained from SigmaAldrich. All reagents were of analytical grade and were used as received without further purification. 2.2. Synthesis of AgNWs First, 100 mM AgNO3 and 10 mM NaCl solutions in EG were prepared. 50 mg PVP (weight ratio of PVP-360000 and PVP-55000 was 2:1) was dissolved in 16 mL EG and heated in an oil bath at 160 °C for 1 h under magnetic stirring. Then, 1 mL of the NaCl solution was added into PVP solution. After 5 min, 6 mL of AgNO3 solution was slowly dropped into the above solution through a syringe. The reaction mixture was held at 160 °C for 25 min. After cooling to room temperature, the AgNWs were crushed out with acetone, centrifuged, and washed with water. Finally, the purified product was dispersed in ethanol. 2.3. Preparation of polymer films ITO glass was cut into 10 mm × 30 mm and 20 mm × 25 mm coupons, which were cleaned according to our previous procedure [50]. After drying, the ITO substrate was vertically inserted into boron trifluoride etherate solution (0.1 M) containing thiophene or 3-thiopheneethanol or 3-thiopheneboronic acid. Electrochemical polymerization was carried out by using ITO glass as working electrode, Ag/AgCl (3 M KCl) as reference electrode and Pt as counter electrode. Potentiostatic polymerization was induced by applying a voltage of 1.5 V for thiophene, and 2.0 V for 3-thiopheneethanol or 3-thiopheneboronic acid across the cell. Polythiothene (PT), poly(3-thiopheneethanol) (P3TE) and poly(3-thiophene boronic acid) (P3TBA) films on ITO glass were obtained after a certain period of time (45 s for thiophene, and 1.5 min for 3-thiopheneethanol or 3-thiopheneboronic acid), respectively. Additionally, the AgNWs dispersion was diluted to 1 mg/mL with ethanol. Then, the dispersion was dropped on cleaned ITO glass in arrays to ensure the uniform distribution of AgNWs on every zone, and scraped longitudinally and transversely by rod coating technique [51]. After drying, the transparent conductive film of AgNWs was obtained. Finally, the AgNWs-coated ITO glass (AgNWs/ITO) was vertically inserted into boron trifluoride etherate solution containing thiophene or 3-thiopheneethanol or 3-thiopheneboronic acid. PT, P3TE and P3TBA films on AgNWs/ITO (PT/AgNWs/ITO, P3TE/AgNWs/ITO and P3TBA/ AgNWs/ITO) were prepared by the above-described method (electrochemical polymerization). 2.4. Fabrication of electrochromic device The gel electrolyte was prepared using the same procedure as reported in our previous work [52]. We fabricated the sandwich structured devices (ITO/polymer layer/gel electrolyte layer/ITO and ITO/ AgNWs/polymer layer/gel electrolyte layer/ITO) by assembling two ITO/glass substrates (polymer layer/ITO or polymer layer/AgNWs/ITO and bare ITO) together with gel electrolyte in contact according to the methods [53–57]. External potentials of +1.2 or 1.5 V and – 1.2 or 2

Solar Energy Materials and Solar Cells 200 (2019) 109919

W. Zhang, et al.

Scheme 1. Schematic representation of the preparation of AgNWs film on ITO glass and the assembly process of corresponding ECD.

3. Results and discussion

1.5 V were applied to the ECDs to achieve switchable color changes [58]. Scheme 1 shows the schematic representation of preparation of AgNWs film on ITO glass and the assembly process of corresponding ECDs.

3.1. XRD pattern and SEM images of AgNWs The XRD pattern of purified AgNWs is shown in Fig. 1a. It can be seen that four diffraction peaks appear centered at 2θ = 38.14°, 44.46°, 64.51°, and 77.48°, which are ascribed to Bragg reflections from the (111), (200), (220), and (311) planes of Ag. These peaks of (111), (200), (220) and (311) are indexed to face-centered cubic structure of silver. No other peaks from impurities are detected, indicating that highly pure AgNWs are successfully prepared. The intensity ratio of the reflections at (111) and (200) is higher relative to the recorded XRD pattern of bulk silver (JCPDS # 04–0783), demonstrating that the (111) plane is the preferred orientation. This is consistent with the previous reports [59–61]. Fig. 1b and c displays the SEM images of the purified as-prepared AgNWs at low and high magnifications. It is found that the average diameter and length of AgNWs are approximately 80 nm and 22 μm, respectively. The length to diameter ratio is about 275. Fig. 2 exhibits the XRD patterns of AgNWs/ITO and PT/AgNWs/ITO surface. For AgNWs/ITO, it is seen that six diffraction peaks appear centered at 2θ = 30.28°, 35.18°, 38.18°, 44.54°, 50.68° and 60.14°. The diffraction peaks at 2θ = 38.18°, 44.54° are ascribed to Bragg reflections from the (111) and (200) planes of Ag. The reflection intensity at (220) and (311) planes of Ag is weak, which is due to the network structure of AgNWs and smaller thickness of AgNWs film on ITO glass. The other four diffraction peaks observed at 30.28°, 35.18°, 50.68° and 60.14° are assigned to the (222), (400), (440) and (622) planes of bodycentered cubic phase In2O3 on glass (JCPDS # 71–2195). For PT/ AgNWs/ITO, the diffraction peaks from AgNWs are basically invisible.

2.5. Characterization The XRD pattern was recorded on a Japan Shimadzu XRD-6000 Xray diffractometer with Cu Kα radiation. The transmittance of AgNWs and polymer films on ITO substrate was measured by using a UV–vis spectrometer (Shimadzu 2550). The morphologies of AgNWs, polymer layer/ITO or polymer layer/AgNWs/ITO surface were evaluated by using a scanning electron microscope (Hitachi SU8000). The CV measurements of polymer layer/ITO and polymer layer/AgNWs/ITO in a 0.1 M lithium perchlorate/acetonitrile solution were carried out on Autolab PGSTAT 302 N potentiostat-galvanostat using polymer layer/ ITO or polymer layer/AgNWs/ITO, Pt plate and saturated calomel as working, counter and reference electrodes, respectively. The electrochemical impedance spectra of polymer layer/ITO and polymer layer/ AgNWs/ITO were determined over the frequency range of 106–10−2 Hz with signal amplitude of 10 mV using the same three-electrode system as that of CV tests. We recorded the spectroelectrochemical properties of ECD based on polymer layer/ITO or polymer layer/AgNWs/ITO by using Autolab PGSTAT 302 N potentiostat with UV–vis spectrometer (Shimadzu 2550).

Fig. 1. XRD pattern (a), low-magnification (b) and high-magnification (c) SEM images of the purified as-prepared AgNWs. 3

Solar Energy Materials and Solar Cells 200 (2019) 109919

W. Zhang, et al.

AgNWs/ITO) were prepared by electrochemical polymerization. As displayed in Fig. 4g-l, AgNWs are relatively evenly distributed in the polymer matrix, and are interlaced with each other to form the reticulation structure. The polymer nanoparticles are homogeneously in situ coated on the surface of AgNWs. Moreover, it is seen that the polymer nanoparticles are orderly arranged along the AgNWs length direction. The average diameters of AgNWs encapsulated by PT, P3TE and P3TBA nanoparticles are about 200, 200 and 160 nm, respectively. Compared with polymer layer/ITO, the AgNWs-polymer composite with reticulated structure shows non-compact film surfaces, which is beneficial to the electrochromic properties of PT, P3TE and P3TBA films.

Fig. 2. XRD patterns of AgNWs/ITO and PT/AgNWs/ITO surface.

This is because that there is a layer of PT film on AgNWs networks, and PT has no distinct characteristic diffraction peak, which induce the very weak diffraction signals of AgNWs.

3.4. Electrochemical behavior of PT, P3TE and P3TBA films on ITO glass The redox behavior of polymer films on ITO glass was evaluated by CV conducted using polymer layer/ITO or polymer layer/AgNWs/ITO as working electrode in 0.1 M LiClO4/CH3CN, respectively. Fig. 5 presents the CV curves of polymer layer/ITO or polymer layer/AgNWs/ITO at a scan rate of 20 mV/s. It can be seen that compared with polymer layer/ITO, the potentials of redox peaks of polymer layer/AgNWs/ITO are basically not changed in the same electrolyte. However, the peak current density of polymer (PT, P3TE or P3TBA) layer/AgNWs/ITO is higher than that of PT, P3TE or P3TBA films on B-ITO at the same scan rate, and the area surrounded by its CV curve is larger than that of PT, P3TE or P3TBA films on B-ITO. According to references [53,62], the greater the peak current density, the higher the electrochemical activity. This indicates that polymer (PT, P3TE or P3TBA) layer/AgNWs/ ITO has high electrochemical activities [63]. So, we can find that the surface modification of ITO electrodes with AgNWs is an effectively method for improving the electrochemical activities of conjugated polymers on ITO glass. To verify the electron conduction and ion transportation crossing the electrode/electrolyte interfaces, the AC impedance spectroscopy was measured in the same electrolyte as the CV test. As shown in Fig. 6, the Nyqvist plots of polymer layer/ITO or polymer layer/AgNWs/ITO start from a semi-circle in high frequency region and are followed by a straight line, which signifies the charge-transfer and ion diffusion process, respectively [56]. The charge-transfer resistance (RCT) can be determined from the diameter of semi-circles of Nyqvist plots. It can be seen that the RCT of PT, P3TE, P3TBA films and corresponding AgNWspolymer composite films is 102.4, 151.5, 124.7, 96.2, 98.4 and 87.3 Ω, respectively. The RCT of polymer (PT, P3TE or P3TBA) layer/AgNWs/ ITO is less than that of PT, P3TE or P3TBA films on B-ITO. The decreased RCT may be due to the increased electric conductivity and ionic conductivity, caused by the incorporation of AgNWs [56]. The lower RCT can be of benefit to electrochemical activities of conjugated polymers as shown in their CV curves, and enhance their electrochromic properties.

3.2. UV–vis transmittance spectra of AgNWs and polymer films on ITO glass To estimate the optical properties of AgNWs and polymer films on ITO glass, the transmittance of bare ITO, AgNWs, and polymer films on ITO substrate in the visible region is measured. Fig. 3 presents the UV–vis transmittance spectra of AgNWs, polythiothene (PT), poly(3thiopheneethanol) (P3TE) and poly(3-thiophene boronic acid) (P3TBA) films on ITO glass. It can be seen that the transmittance of AgNWs/ITO is lower than that of B-ITO. The transmittance of AgNWs/ITO decreases slightly due to the presence of AgNWs, but still over 81% at 597 nm. Compared with B-ITO and AgNWs/ITO, the transmittance of polymer/ ITO or polymer/AgNWs/ITO in the range of 370–600 nm decreases. This is caused by UV–vis absorption of the corresponding polymer films. Additionally, the mean sheet resistance of AgNWs/ITO is measured by four-point probe resistance tester, which is 6.2 Ω/□. Clearly, the conductivity of AgNWs/ITO is higher than that of B-ITO. The thickness of AgNWs and polymer films is measured using a Bruker Dektak XT surface profiler. For AgNWs, PT/AgNWs, P3TE/AgNWs and P3TBA/AgNWs layer, their thickness is about 0.15, 0.55, 0.60 and 0.63 μm, respectively. 3.3. SEM images of PT, P3TE and P3TBA films on ITO glass Fig. 4 shows the low-magnification and high-magnification SEM images of (a, d) PT/ITO, (b, e) P3TE/ITO, (c, f) P3TBA/ITO, (g, j) PT/ AgNWs/ITO, (h, k) P3TE/AgNWs/ITO, and (i, l) P3TBA/AgNWs/ITO surface. It can be seen from Fig. 4a–f that the films of PT, P3TE and P3TBA are made up of many nanoparticles exhibiting spherical/or globular morphology, which shows variation in terms of diameter. The average particle sizes of PT, P3TE and P3TBA are about 100, 50 and 100 nm, respectively. In addition, we find the P3TE or P3TBA nanoparticles aggregates formed by particle-cluster mechanism on the surface of films. After AgNWs is coated on ITO glass, PT, P3TE and P3TBA films on AgNWs/ITO (PT/AgNWs/ITO, P3TE/AgNWs/ITO and P3TBA/

Fig. 3. UV–vis transmittance spectra of AgNWs, PT (a), P3TE (b) and P3TBA (c) films on ITO glass. 4

Solar Energy Materials and Solar Cells 200 (2019) 109919

W. Zhang, et al.

Fig. 4. Low-magnification and high-magnification SEM images of (a, d) PT/ITO, (b, e) P3TE/ITO, (c, f) P3TBA/ITO, (g, j) PT/AgNWs/ITO, (h, k) P3TE/AgNWs/ITO, and (i, l) P3TBA/AgNWs/ITO surface.

Fig. 5. Cyclic voltammetry curves of polymer layer/ITO or polymer layer/AgNWs/ITO.

Fig. 6. Electrochemical impedance spectra of polymer layer/ITO or polymer layer/AgNWs/ITO. 5

Solar Energy Materials and Solar Cells 200 (2019) 109919

W. Zhang, et al.

Fig. 7. Transmittance spectra of ECD based on (a) PT/ITO and (d) PT/AgNWs/ITO in the visible range under various potentials; Optical transmittance at 715 nm for ECD based on (b) PT/ITO and (e) PT/AgNWs/ITO under the step potential oscillating between + 1.2 and ‒ 1.2 V with 20 s interval, and (c, f) larger image of the first two cycles, respectively.

find that the thickness of PT films does have effect on the color change. The transmittance of ECDs is much lower as the film thickness increases, as shown in Fig. S1. That means the ECD is darker as the thickness of PT films increases. The optical contrast of ECDs (the applied voltage is ± 1.2 V) remains nearly the same for all thickness possibly due to the choice of applied voltage. This indicates that the thickness of PT films has little effect on the optical contrast of ECDs, which is more sensitive to voltage changes. The higher the applied voltage, the greater the optical contrast. However, the cyclic stability of ECDs will be reduced by increasing the applied voltage. Therefore, we choose a lower applied voltage ( ± 1.2 V) to test the performance of ECDs based on PT/ITO. Except for the optical contrast, the response time is another important parameter of electrochromic properties, which is related to the material nature and size of anion and cation in electrolyte [53]. The coloration and bleaching time of ECD can be estimated according to the time needed for achieving 90% of their total transmittance changes under the step potential oscillating between +1.2 and ‒ 1.2 V with 20 s interval. As displayed in Fig. 7c and f, the coloration time (tc) and bleaching time (tb) of ECD based on PT/ITO are 11.3 and 7.2 s, respectively. For the ECD based on PT/AgNWs/ITO, its coloration time and bleaching time are 2.6 and 1.6 s, which are much shorter than those of ECD based on PT/ITO. Hereinafter, the average switching speed (Sp) is defined as optical contrast per unit time, which is calculated from: Sp = 0.9 × ΔT/t. Thus, the average switching speeds (Spc and Spb) of coloration and bleaching process can be obtained. The Spc and Spb of ECD based on PT/AgNWs/ITO are 4.15 and 6.75%/s, which are higher than those (0.56 and 0.88%/s) of ECD based on PT/ITO. This indicates that the ECD based on PT/AgNWs/ITO has faster switching speed under the same experimental conditions. It is because that the three-dimensional hollow framework of AgNWs networks facilitates the insertion/ extraction of ions, inducing the increase of switching speed. In order to further confirm the above conclusions, we investigate the electrochromic properties of ECD based on the other two polymers (P3TE and P3TBA). It is well-known that the coplanarity of polythiophene can be regulated by changing the steric hindrance of 3substituents of thiophene ring, so as to adjust the effective conjugation degree of polymer chain and realize the control of the electrochromic performance. Fig. 8a and d presents the transmittance spectra of ECD

3.5. Electrochromic properties of PT, P3TE and P3TBA films on ITO glass To gain an in-depth understanding of the influence of AgNWs on the electrochromic properties of polymer, the optical transmittance of corresponding ECDs in the visible region under various potentials is measured. It is seen from Fig. 7a and d that when the applied potential is gradually reduced from high positive potential, its color changes from light blue to light red. When the applied potential increases form 0 to +1.2 V, the amplitude of change in transmittance of ECD based on PT/ AgNWs/ITO is larger than that of ECD based on PT/ITO. Fig. 7b and e shows the optical transmittance at 715 nm for ECD based on PT/ITO or PT/AgNWs/ITO under the step potential oscillating between +1.2 and ‒ 1.2 V with 20 s interval. As one of major electrochromic properties, optical contrast (ΔT) represents the maximum transmittance difference between the coloration state (Tc) and bleaching state (Tb) [52]. For the ECD based on PT/ITO, it is obvious that the initial optical contrast under +1.2/‒ 1.2 V potential is 7% at 715 nm. The optical contrast decreases gradually with the increase in cycle number. After 90 cycles, the optical contrast reduces to 5%. The decrease is approximately 29% in transmittance changes from a higher value to a lower value under ambient conditions, indicating that the cyclic stability of ECD based on PT/ITO is not good. Compared with ECD based on PT/ITO, the initial optical contrast of ECD based on PT/AgNWs/ITO under +1.2/‒ 1.2 V potential is 12%, increasing 71% (7 → 12%). The optical contrast remains basically unchanged as the number of cycles increases, and can still reach 11% after 90 cycles. Its optical contrast decreases by approximately 8% in transmittance changes, demonstrating that the device has a stable electrochromic performance under the applied voltage. In order to investigate the influence of thickness of polymer films on the optical contrast of ECDs, PT films with different polymerization times (30 s, 60 s and 90 s) are prepared using an electrochemical method. The thickness of PT films is 0.45, 0.65, and 1.2 μm, respectively. Fig. S1 shows the transmittance spectra of ECDs based on PT/ITO in the visible range under varied voltages (‒ 1.2 V, + 1.2 V, ‒ 1.5 V and +1.5 V). It can be seen that when the applied voltage changes from ‒ 1.2 V to +1.2 V, the optical contrast of ECDs based on PT/ITO is 6, 8 and 8% for PT films with different thickness (0.45, 0.65, and 1.2 μm). When the applied voltage changes from ‒ 1.5 V to +1.5 V, the optical contrast of corresponding ECDs increases to 11, 14, and 15%, respectively. We can 6

Solar Energy Materials and Solar Cells 200 (2019) 109919

W. Zhang, et al.

Fig. 8. Transmittance spectra of ECD based on (a) P3TE/ITO and (d) P3TE/AgNWs/ITO in the visible range under various potentials; Optical transmittance at 750 nm for ECD based on (b) P3TE/ITO and (e) P3TE/AgNWs/ITO under the step potential oscillating between + 1.5 and ‒ 1.5 V with 20 s interval, and (c, f) larger image of the first two cycles, respectively.

time are 5.7 and 0.9 s, which are much shorter than those of ECD based on P3TBA/ITO. This result further confirms that the surface modification of ITO electrodes with AgNWs is an effectively method for improving the switching speed of ECPs on ITO glass. According to references [64–66], we can find that the magnitude of ΔT measured for ECDs based on ECP/ITO or ECP/AgNWs/ITO in this paper is close to the reported results. The slight decrease of ΔT is due to the larger resistance of solid ECDs and slower ion diffusion rate. The optical images of ECDs based on (a) PT/AgNWs/ITO, (b) P3TE/AgNWs/ITO, and (c) P3TBA/ AgNWs/ITO in reduced and oxidized states are presented in Fig. S2 (Supplementary Material). For better evaluating the performance of the ECDs, the coloration efficiency (ƞCE) of ECDs is determined with a time step of 20 s. Fig. S3 shows the current-time responses of the ECDs based on ECP/ITO and ECP/AgNWs/ITO under a certain applied voltage. The ƞCE is calculated by the equations: ƞCE = ΔOD/Q, and ΔOD = log[Tb/Tc] [6,67]. ΔOD represents the change in optical density at the wavelength λ, and Q is the injected/ejected charge per unit of EC material area. According to the above equation, the EC parameters of ECDs based on ECP/ITO and ECP/AgNWs/ITO are obtained (see Table 1). It can be seen that the incorporation of AgNWs induces the increase of Q and ƞCE of ECDs based on ECP/AgNWs/ITO. Additionally, the ƞCE values are in accordance with the values (between 100 and 300 cm2/C) cited in the literature for polymers obtained from thiophene and its derivatives [66,68]. From the above analysis, it can be seen that the amplitude of change in transmittance of ECD based on electrochromic polymer (ECP)/ AgNWs/ITO is larger than that of ECD based on ECP/ITO under the same applied voltage. After 90 cycles, the optical contrast of ECD based on ECP/ITO decreases significantly. However, the optical contrast of ECD based on ECP/AgNWs/ITO only shows very slight change, indicating that it has a stable electrochromic performance. Additionally, the switching speed of ECD based on ECP/AgNWs/ITO is faster than that of ECD based on ECP/ITO. In order to reveal the essential reason behind these phenomena, we need to elucidate the electrochromic mechanism of ECP (PT, P3TE and P3TBA). According to the literature [69–71], the PT, P3TE and P3TBA films can be reversibly undoped (and subsequently redoped) by electrochemical reduction (oxidation). The electrochromism behind the PT, P3TE and P3TBA devices can be

based on P3TE/ITO or P3TE/AgNWs/ITO in the visible range under various potentials. It can be seen that when the applied potential increases form 0 to +1.5 V, the amplitude of change in transmittance of ECD based on P3TE/AgNWs/ITO is larger than that of ECD based on P3TE/ITO. As shown in Fig. 8b and e, the initial optical contrast of ECD based on P3TE/ITO under +1.5/‒ 1.5 V potential is 10% at 750 nm. After 90 cycles, the optical contrast reduces to 7%. The decrease is approximately 30% in transmittance changes from a higher value to a lower value. Compared with ECD based on P3TE/ITO, the initial optical contrast of ECD based on P3TE/AgNWs/ITO under +1.5/‒ 1.5 V potential is 19%, increasing 90% (10 → 19%). The optical contrast reaches 16% after 90 cycles, decreasing by approximately 16% in transmittance changes. This indicates that the ECD based on P3TE/ AgNWs/ITO has a stable electrochromic performance under the applied voltage. Additionally, it is found from Fig. 8c and f that the coloration time and bleaching time of ECD based on P3TE/ITO are 10.1 and 1.3 s, respectively. For the ECD based on P3TE/AgNWs/ITO, its tc and tb are shorter than those of ECD based on P3TE/ITO. It is because that the introduction of AgNWs accelerates the switching speed of ECDs. Fig. 9a and d displays the transmittance spectra of ECD based on P3TBA/ITO or P3TBA/AgNWs/ITO in the visible range under various potentials. Clearly, it can be seen that when the applied potential increases form 0 to +1.5 V, the amplitude of change in transmittance of ECD based on P3TBA/AgNWs/ITO is larger than that of ECD based on P3TBA/ITO. Fig. 9b and e presents the optical transmittance at 753 nm for ECD based on P3TBA/ITO or P3TBA/AgNWs/ITO under the step potential oscillating between +1.5 and ‒ 1.5 V with 20 s interval. The initial optical contrast of ECD based on P3TBA/ITO is 8%, and the optical contrast reduces to 4% after 90 cycles. The decrease is approximately 50% in transmittance changes, indicating that the cyclic stability of ECD based on P3TBA/ITO is not good. Compared with ECD based on P3TBA/ITO, the initial optical contrast of ECD based on P3TBA/AgNWs/ITO is 14%, increasing 75% (8 → 14%). The optical contrast reaches 12% after 90 cycles, decreasing by approximately 14% in transmittance changes. This demonstrates that the ECD based on P3TBA/AgNWs/ITO has a stable electrochromic performance. Moreover, as shown in Fig. 9c and f, the coloration time and bleaching time of ECD based on P3TBA/ITO are 13.1 and 3.9 s, respectively. For the ECD based on P3TBA/AgNWs/ITO, its coloration time and bleaching 7

Solar Energy Materials and Solar Cells 200 (2019) 109919

W. Zhang, et al.

Fig. 9. Transmittance spectra of ECD based on (a) P3TBA/ITO and (d) P3TBA/AgNWs/ITO in the visible range under various potentials; Optical transmittance at 753 nm for ECD based on (b) P3TBA/ITO and (e) P3TBA/AgNWs/ITO under the step potential oscillating between + 1.5 and ‒ 1.5 V with 20 s interval, and (c, f) larger image of the first two cycles, respectively.

electrochromic system. The large surface area of AgNWs coated with ECP can reduce the biasing potential required to change the color of the electrochromic film [73]. Additionally, AgNWs have excellent electrical conductivity, improving the conductivity of the composite films. It is known that the networks of AgNWs are comprised of a 3-dimensional (3D) hollow framework in which individual nanowires are connected to each other to establish an electrical pathway [74–76]. This structure allows AgNWs film to simultaneously exhibit transparency and conductivity. So, the optical contrast of ECD based on ECP/AgNWs/ITO is higher than that of ECD based on ECP/ITO under the same applied voltage, and its response time is shorter. Compared with ECD based on ECP/ITO, the ECD based on ECP/AgNWs/ITO exhibits a stable electrochromic performance.

described by Eq. (1):

(1) Where ClO4− is the salvation counter-ion. The doping/dedoping reaction of PT, P3TE and P3TBA films is carried out under the applied voltage, and is a kinetic process determined by the material nature and its electrical conductivity and ion diffusion ability. Fig. 10 displays the schematic representation of the behaviors of ion diffusion and migration in ECDs during the electrochemical redox process. According to the electrochromic behaviors of ECD based on ECP/AgNWs/ITO, we find that the influence of AgNWs on the electrochromic properties of ECP includes: i) increasing the optical contrast; ii) decreasing the response time; iii) improving the cyclic stability. This is caused by geometrical effect of stacking structure, large surface area and its high conductivity [53]. The well-defined geometric structure of ECP/AgNWs films is formed by the AgNWs coated with ECP, which provides ion storage space and transport channel [44,72]. Moreover, the ECP is synthesized via in situ polymerization and coated on the surface of AgNWs, and then one novel core-shell composite is obtained. The ions doping and dedoping in the composite film are easier than those in the compact pure ECP film due to the thin ECP coating layer and the large surface area in the composite film [44]. These stacking composite structures benefit the diffusion and migration of ions in the

4. Conclusions In summary, the ECP/AgNWs/ITO electrode was fabricated by synthesizing AgNWs and coating them onto the ITO substrate, and the corresponding devices were assembled. The ECP/AgNWs films on the electrode have the stacking structure, exhibiting high electrochemical activities. A highly optical contrast, cyclic stability and short response time are achieved in ECD based on ECP/AgNWs/ITO after 90 cycles in polymer gel electrolyte. Based on the analysis of ions doping and dedoping in ECD with ECP/AgNWs/ITO electrode, it is demonstrated that geometrical effect of stacking structure benefits the diffusion and migration of ions in the electrochromic system, and the large surface area of AgNWs coated with ECP can reduce the biasing potential required to change the color of the ECD. Additionally, AgNWs have excellent

Table 1 Electrochromic parameters of ECDs based on ECP/ITO and ECP/AgNWs/ITO. Electrochromic devices

ΔT (%)

tc (s)

tb (s)

Spc (%/s)

Spb (%/s)

Q (mC/cm2)

ƞCE (cm2/C)

ITO/PT/Gel electrolyte/ITO ITO/AgNWs/PT/Gel electrolyte/ITO ITO/P3TE/Gel electrolyte/ITO ITO/AgNWs/P3TE/Gel electrolyte/ITO ITO/P3TBA/Gel electrolyte/ITO ITO/AgNWs/P3TBA/Gel electrolyte/ITO

7 12 10 19 8 14

11.3 2.6 10.1 8.7 13.1 5.7

7.2 1.6 1.3 0.9 3.9 0.9

0.56 4.15 0.89 1.97 0.55 2.21

0.88 6.75 6.92 19.0 1.85 14.0

0.27 0.43 0.41 0.64 0.38 0.59

178 200 161 202 154 183

8

Solar Energy Materials and Solar Cells 200 (2019) 109919

W. Zhang, et al.

Fig. 10. Schematic representation of the behaviors of ion diffusion and migration in ECDs during the electrochemical redox process.

electrical conductivity, improving the conductivity of ECP/AgNWs films. Thus, the ECD achieves a highly optical contrast, stable cycling and short response time. Our present work provides an important insight into the design principles for the practical applications of highly electrochemically active electrode and opens up a direction for the realization of the high-performance electrochromic devices based on AgNWs and ECPs.

[9]

[10] [11]

Acknowledgements

[12]

This work was financially supported by the National Natural Science Foundation of China (No. 51303147, 61704133, 21772152 and 61701386), Natural Science Foundation of Shaanxi Province of China (No. 2019JM-225 and 2017JQ5060), Natural Science Foundation of Hubei Province of China (No. 2018CFB520), and the Opening Project of Key Laboratory of Optoelectronic Chemical Materials and Devices, Ministry of Education, Jianghan University (No. JDGD-201803).

[13] [14] [15]

[16]

Appendix A. Supplementary data [17]

Supplementary data to this article can be found online at https:// doi.org/10.1016/j.solmat.2019.109919.

[18]

References

[19]

[1] G.W. Kim, Y.C. Kim, I.J. Ko, J.H. Park, H.W. Bae, R. Lampande, J.H. Kwon, Highperformance electrochromic optical shutter based on fluoran dye for visibility enhancement of augmented reality display, Adv. Optical Mater. 6 (2018) 1701382. [2] H. Kai, W. Suda, Y. Ogawa, K. Nagamine, M. Nishizawa, Intrinsically stretchable electrochromic display by a composite film of poly(3,4-ethylenedioxythiophene) and polyurethane, ACS Appl. Mater. Interfaces 9 (2017) 19513–19518. [3] N.C. Davy, M. Sezen-Edmonds, J. Gao, X. Lin, A. Liu, N. Yao, A. Kahn, Y.L. Loo, Pairing of near-ultraviolet solar cells with electrochromic windows for smart management of the solar spectrum, Nat. Energy 2 (2017) 17104. [4] G. Cai, P. Darmawan, X. Cheng, P.S. Lee, Inkjet printed large area multifunctional smart windows, Adv. Energy Mater. 7 (2017) 1602598. [5] P. Zhang, F. Zhu, F. Wang, J. Wang, R. Dong, X. Zhuang, O.G. Schmidt, X. Feng, Stimulus-responsive micro-supercapacitors with ultrahigh energy density and reversible electrochromic window, Adv. Mater. 29 (2017) 1604491. [6] S. Lin, X. Bai, H. Wang, H. Wang, J. Song, K. Huang, C. Wang, N. Wang, B. Li, M. Lei, H. Wu, Roll-to-roll production of transparent silver-nanofiber-network electrodes for flexible electrochromic smart windows, Adv. Mater. 29 (2017) 1703238. [7] P. Zou, Y. Zhao, A.D. Douglass, D.R. Hochbaum, D. Brinks, C.A. Werley, D.J. Harrison, R.E. Campbell, A.E. Cohen, Bright and fast multicoloured voltage reporters via electrochromic FRET, Nat. Commun. 5 (2014) 4625. [8] K. Liu, J. Varghese, J.Y. Gerasimov, A.O. Polyakov, M. Shuai, J. Su, D. Chen,

[20]

[21]

[22]

[23]

[24]

[25]

[26]

9

W. Zajaczkowski, A. Marcozzi, W. Pisula, B. Noheda, T.T.M. Palstra, N.A. Clark, A. Herrmann, Controlling the volatility of the written optical state in electrochromic DNA liquid crystals, Nat. Commun. 7 (2016) 11476. A.M. Österholm, D.E. Shen, J.A. Kerszulis, R.H. Bulloch, M. Kuepfert, A.L. Dyer, J.R. Reynolds, Four shades of brown: tuning of electrochromic polymer blends toward high-contrast eyewear, ACS Appl. Mater. Interfaces 7 (2015) 1413–1421. C. Xu, G.T. Stiubianu, A.A. Gorodetsky, Adaptive infrared-reflecting systems inspired by cephalopods, Science 359 (2018) 1495–1500. J. Mandal, S. Du, M. Dontigny, K. Zaghib, N. Yu, Y. Yang, Li4Ti5O12: a visible-toinfrared broadband electrochromic material for optical and thermal management, Adv. Funct. Mater. 28 (2018) 1802180. H. Yu, S. Shao, L. Yan, H. Meng, Y. He, C. Yao, P. Xu, X. Zhang, W. Hu, W. Huang, Side-chain engineering of green color electrochromic polymer materials: toward adaptive camouflage application, J. Mater. Chem. C 4 (2016) 2269–2273. W. Wu, M. Wang, J. Ma, Y. Cao, Y. Deng, Electrochromic metal oxides: recent progress and prospect, Adv. Electron. Mater. 4 (2018) 1800185. J. Jensen, M. Hösel, A.L. Dyer, F.C. Krebs, Development and manufacture of polymer-based electrochromic devices, Adv. Funct. Mater. 25 (2015) 2073–2090. M. Sassi, M.M. Salamone, R. Ruffo, G.E. Patriarca, C.M. Mari, G.A. Pagani, U. Posset, L. Beverina, State-of-the-art neutral tint multichromophoric polymers for high-contrast see-through electrochromic devices, Adv. Funct. Mater. 26 (2016) 5240–5246. Y. Kim, H. Shin, M. Han, S. Seo, W. Lee, J. Na, C. Park, E. Kim, Energy saving electrochromic polymer windows with a highly transparent charge-balancing layer, Adv. Funct. Mater. 27 (2017) 1701192. Y. Zhou, J. Fang, H. Wang, H. Zhou, G. Yan, Y. Zhao, L. Dai, T. Lin, Multicolor electrochromic fibers with helix-patterned electrodes, Adv. Electron. Mater. 4 (2018) 1800104. Q. Du, Y. Wei, J. Zheng, C. Xu, Donor-π-bridge-acceptor type polymeric materials with pendant electron-withdrawing groups for electrochromic applications, Electrochim. Acta 132 (2014) 258–264. S. Ming, S. Zhen, K. Lin, L. Zhao, J. Xu, B. Lu, Thiadiazolo[3,4-c]pyridine as an acceptor toward fast-switching green donor-acceptor-type electrochromic polymer with low bandgap, ACS Appl. Mater. Interfaces 7 (2015) 11089–11098. J.A. Kerszulis, R.H. Bulloch, N.B. Teran, R.M.W. Wolfe, J.R. Reynolds, Relax: a sterically relaxed donor-acceptor approach for color tuning in broadly absorbing, high contrast electrochromic polymers, Macromolecules 49 (2016) 6350–6359. N.B. Teran, J.R. Reynolds, Discrete donor-acceptor conjugated systems in neutral and oxidized states: implications toward molecular design for high contrast electrochromics, Chem. Mater. 29 (2017) 1290–1301. Y. Guo, W. Li, H. Yu, D.F. Perepichka, H. Meng, Flexible asymmetric supercapacitors via spray coating of a new electrochromic donor-acceptor polymer, Adv. Energy Mater. 7 (2017) 1601623. H.-S. Liu, B.-C. Pan, D.-C. Huang, Y.-R. Kung, C.-M. Leu, G.-S. Liou, Highly transparent to truly black electrochromic devices based on an ambipolar system of polyamides and viologen, NPG Asia Mater. 9 (2017) e388. B. Lu, S. Zhen, S. Zhang, J. Xu, G. Zhao, Highly stable hybrid selenophene-3,4ethylenedioxythiophene as electrically conducting and electrochromic polymers, Polym. Chem. 5 (2014) 4896–4908. K. Lin, S. Ming, S. Zhen, Y. Zhao, B. Lu, J. Xu, Molecular design of DBT/DBF hybrid thiophenes π-conjugated systems and comparative study of their electropolymerization and optoelectronic properties: from comonomers to electrochromic polymers, Polym. Chem. 6 (2015) 4575–4587. K. Lin, Y. Zhao, S. Ming, H. Liu, S. Zhen, J. Xu, B. Lu, Blue to light gray electrochromic polymers from dodecyl-derivatized thiophene bis-substituted

Solar Energy Materials and Solar Cells 200 (2019) 109919

W. Zhang, et al.

[27]

[28]

[29]

[30]

[31] [32]

[33]

[34]

[35]

[36]

[37]

[38]

[39]

[40]

[41]

[42]

[43]

[44]

[45]

[46]

[47]

[48]

[49]

[50]

[51]

[52]

dibenzothiophene/dibenzofuran, J. Polym. Sci., Part A: Polym. Chem. 54 (2016) 1468–1478. K. Lin, S. Chen, B. Lu, J. Xu, Hybrid π-conjugated polymers from dibenzo pentacyclic centers: precursor design, electrosynthesis and electrochromics, Sci. China Chem. 60 (2017) 38–53. K. Cao, D.E. Shen, A.M. Österholm, J.A. Kerszulis, J.R. Reynolds, Tuning color, contrast, and redox stability in high gap cathodically coloring electrochromic polymers, Macromolecules 49 (2016) 8498–8507. M. Ouyang, Y. Yang, X. Lv, Y. Han, S. Huang, Y. Dai, C. Su, Y. Lv, M. Sumita, C. Zhang, Enhanced electrochromic switching speed and electrochemical stability of conducting polymer film on an ionic liquid functionalized ITO electrode, New J. Chem. 39 (2015) 5329–5335. S.L. Pittelli, D.E. Shen, A.M. Österholm, J.R. Reynolds, Chemical oxidation of polymer electrodes for redox active devices: stabilization through interfacial interactions, ACS Appl. Mater. Interfaces 10 (2018) 970–978. A. Garreau, J.L. Duvail, Recent advances in optically active polymer-based nanowires and nanotubes, Adv. Optical Mater. 2 (2014) 1122–1140. C.-W. Hu, T. Sato, J. Zhang, S. Moriyama, M. Higuchi, Three-dimensional Fe(II)based metallo-supramolecular polymers with electrochromic properties of quick switching, large contrast, and high coloration efficiency, ACS Appl. Mater. Interfaces 6 (2014) 9118–9125. M. Ouyang, S.-B. Huang, Y.-G. Han, X.-J. Lv, Y. Yang, Y.-Y. Dai, Y.-K. Lv, C. Zhang, Enhanced electrochromic performance of ordered porous monolayer PBTB film using amine-modified polystyrene spheres as a template, Acta Phys. - Chim. Sin. 31 (2015) 476–482. H. Zhang, H. Qu, H. Lv, S. Hou, K. Zhang, J. Zhao, X. Li, E. Frank, Y. Li, Improved electrochromic performance of poly(3,4-ethylenedioxythiophene) by incorporating a three-dimensionally ordered macroporous structure, Chem. Asian J. 11 (2016) 2882–2888. B.-C. Pan, W.-H. Chen, S.-H. Hsiao, G.-S. Liou, A facile approach to prepare porous polyamide films with enhanced electrochromic performance, Nanoscale 10 (2018) 16613–16620. W.T. Neo, X. Li, S.J. Chua, K.S.L. Chong, J. Xu, Enhancing the electrochromic performance of conjugated polymers using thermal nanoimprint lithography, RSC Adv. 7 (2017) 49119–49124. L. Qin, Z. Ding, M. Hanif, J. Jiang, L. Liu, Y. Mo, Z. Xie, Y. Ma, Poly(3,4-dioxythiophene) soft nano-network with a compatible ion transporting channel for improved electrochromic performance, Polym. Chem. 7 (2016) 6954–6963. P. Jia, A.A. Argun, J. Xu, S. Xiong, J. Ma, P.T. Hammond, X. Lu, High-contrast electrochromic thin films via layer-by-layer assembly of starlike and sulfonated polyaniline, Chem. Mater. 22 (2010) 6085–6091. G. Cai, J. Tu, D. Zhou, J. Zhang, Q. Xiong, X. Zhao, X. Wang, C. Gu, Multicolor electrochromic film based on TiO2@polyaniline core/shell nanorod array, J. Phys. Chem. C 117 (2013) 15967–15975. A. Zhou, X. Liu, Y. Dou, S. Guan, J. Han, M. Wei, The fabrication of oriented organic-inorganic ultrathin films with enhanced electrochromic properties, J. Mater. Chem. C 4 (2016) 8284–8290. T. Xu, E.C. Walter, A. Agrawal, C. Bohn, J. Velmurugan, W. Zhu, H.J. Lezec, A.A. Talin, High-contrast and fast electrochromic switching enabled by plasmonics, Nat. Commun. 7 (2016) 10479. Q. Zhang, C.-Y. Tsai, T. Abidin, J.-C. Jiang, W.-R. Shie, L.-J. Li, D.-J. Liaw, Transmissive-to-black fast electrochromic switching from a long conjugated pendant group and a highly dispersed polymer/SWNT, Polym. Chem. 9 (2018) 619–626. M. Nunes, C. Moura, A.R. Hillman, C. Freire, Multicolour electrochromic film based on a TiO2@poly[Ni(salen)] nanocomposite with excellent electrochemical stability, Langmuir 33 (2017) 6826–6837. F. Hu, J. Xu, S. Zhang, J. Jiang, B. Yan, Y. Gu, M. Jiang, S. Lin, S. Chen, Core/shell structured halloysite/polyaniline nanotubes with enhanced electrochromic properties, J. Mater. Chem. C 6 (2018) 5707–5715. Y. Shi, Y. Zhang, K. Tang, Y. Song, J. Cui, X. Shu, Y. Wang, J. Liu, Y. Wu, In situ growth of PEDOT/graphene oxide nanostructures with enhanced electrochromic performance, RSC Adv. 8 (2018) 13679–13685. D. Zhou, B. Che, X. Lu, Rapid one-pot electrodeposition of polyaniline/manganese dioxide hybrids: a facile approach to stable high-performance anodic electrochromic materials, J. Mater. Chem. C 5 (2017) 1758–1766. S. Zhang, G. Sun, Y. He, R. Fu, Y. Gu, S. Chen, Preparation, characterization, and electrochromic properties of nanocellulose-based polyaniline nanocomposite films, ACS Appl. Mater. Interfaces 9 (2017) 16426–16434. J. Xiong, S. Li, Y. Ye, J. Wang, K. Qian, P. Cui, D. Gao, M.-F. Lin, T. Chen, P.S. Lee, A deformable and highly robust ethyl cellulose transparent conductor with a scalable silver nanowires bundle micromesh, Adv. Mater. 30 (2018) 1802803. P. Xue, S. Liu, X. Shi, C. Sun, C. Lai, Y. Zhou, D. Sui, Y. Chen, J. Liang, A hierarchical silver-nanowire-graphene host enabling ultrahigh rates and superior long-term cycling of lithium-metal composite anodes, Adv. Mater. 30 (2018) 1804165. W. Zhang, W. Ju, X. Wu, Y. Wang, Q. Wang, H. Zhou, S. Wang, C. Hu, Structure, stability and electrochromic properties of polyaniline film covalently bonded to indium tin oxide substrate, Appl. Surf. Sci. 367 (2016) 542–551. Y. Jia, C. Chen, D. Jia, S. Li, S. Ji, C. Ye, Silver nanowire transparent conductive films with high uniformity fabricated via a dynamic heating method, ACS Appl. Mater. Interfaces 8 (2016) 9865–9871. W. Zhang, X. Wu, Y. Wang, C. Hu, Q. Wang, S. Zhu, High-performance

[53]

[54]

[55]

[56]

[57]

[58]

[59]

[60]

[61]

[62]

[63]

[64]

[65] [66]

[67] [68]

[69]

[70]

[71]

[72]

[73]

[74]

[75] [76]

10

polythiothene film covalently bonded to ITO electrode: synthesis and electrochromic properties, Sol. Energy Mater. Sol. Cells 177 (2018) 15–22. S. Xiong, Z. Li, M. Gong, X. Wang, J. Fu, Y. Shi, B. Wu, J. Chu, Covalently bonded polyaniline and para-phenylenediamine functionalized graphene oxide: how the conductive two-dimensional nanostructure influences the electrochromic behaviors of polyaniline, Electrochim. Acta 138 (2014) 101–108. B. He, W.T. Neo, T.L. Chen, L.M. Klivansky, H. Wang, T. Tan, S.J. Teat, J. Xu, Y. Liu, Low bandgap conjugated polymers based on a nature-inspired bay-annulated indigo (Bai) acceptor as stable electrochromic materials, ACS Sustain. Chem. Eng. 4 (2016) 2797–2805. S. Xiong, J. Wei, P. Jia, L. Yang, J. Ma, X. Lu, Water-processable polyaniline with covalently bonded single-walled carbon nanotubes: enhanced electrochromic properties and impedance analysis, ACS Appl. Mater. Interfaces 3 (2011) 782–788. S. Xiong, J. Lan, S. Yin, Y. Wang, Z. Kong, M. Gong, B. Wu, J. Chu, X. Wang, R. Zhang, Y. Li, Enhancing the electrochromic properties of polyaniline via coordinate bond tethering the polyaniline with gold colloids, Sol. Energy Mater. Sol. Cells 177 (2018) 134–141. J. Chu, D. Lu, B. Wu, X. Wang, M. Gong, R. Zhang, S. Xiong, Synthesis and electrochromic properties of conducting polymers: polyaniline directly grown on fluorine-doped tin oxide substrate via hydrothermal techniques, Sol. Energy Mater. Sol. Cells 177 (2018) 70–74. D. Kim, J. Kim, Y. Ko, K. Shim, J.H. Kim, J. You, A facile approach for constructing conductive polymer patterns for application in electrochromic devices and flexible microelectrodes, ACS Appl. Mater. Interfaces 8 (2016) 33175–33182. R.R. da Silva, M. Yang, S.-I. Choi, M. Chi, M. Luo, C. Zhang, Z.-Y. Li, P.H.C. Camargo, S.J.L. Ribeiro, Y. Xia, Facile synthesis of sub-20 nm silver nanowires through a bromide-mediated polyol method, ACS Nano 10 (2016) 7892–7900. C.-H. Zhu, L.-M. Li, J.-H. Wang, Y.-P. Wu, Y. Liu, Three-dimensional highly conductive silver nanowires sponges based on cotton-templated porous structures for stretchable conductors, RSC Adv. 7 (2017) 51–57. M.B. Gebeyehu, T.F. Chala, S.-Y. Chang, C.-M. Wu, J.-Y. Lee, Synthesis and highly effective purification of silver nanowires to enhance transmittance at low sheet resistance with simple polyol and scalable selective precipitation method, RSC Adv. 7 (2017) 16139–16148. H. Wu, S.A. Shevlin, Q. Meng, W. Guo, Y. Meng, K. Lu, Z. Wei, Z. Guo, Flexible and binder-free organic cathode for high-performance lithium-ion batteries, Adv. Mater. 26 (2014) 3338–3343. S. Xiong, Y. Shi, J. Chu, M. Gong, B. Wu, X. Wang, Preparation of high-performance covalently bonded polyaniline nanorods/graphene supercapacitor electrode materials using interfacial copolymerization approach, Electrochim. Acta 127 (2014) 139–145. Y. Pang, H. Xu, X. Li, H. Ding, Y. Cheng, G. Shi, L. Jin, Electrochemical synthesis, characterization, and electrochromic properties of poly(3-chlorothiophene) and its copolymer with 3-methylthiophene in a room temperature ionic liquid, Electrochem. Commun. 8 (2006) 1757–1763. S. Varis, M. Ak, C. Tanyeli, I.M. Akhmedov, L. Toppare, A soluble and multichromic conducting polythiophene derivative, Eur. Polym. J. 42 (2006) 2352–2360. K. Lin, S. Zhang, H. Liu, Y. Zhao, Z. Wang, J. Xu, Effects on the electrochemical and electrochromic properties of 3 linked polythiophene derivative by the introduction of polyacrylate, Int. J. Electrochem. Sci. 10 (2015) 7720–7731. V.K. Thakur, G. Ding, J. Ma, P.S. Lee, X. Lu, Hybrid materials and polymer electrolytes for electrochromic device applications, Adv. Mater. 24 (2012) 4071–4096. Y. Pang, X. Li, H. Ding, G. Shi, L. Jin, Electropolymerization of high quality electrochromic poly(3-alkyl-thiophene)s via a room temperature ionic liquid, Electrochim. Acta 52 (2007) 6172–6177. H. Zhang, J. Pang, X. Ai, Y. Cao, H. Yang, S. Lu, Poly(3-butylthiophene)-based positive-temperature-coefficient electrodes for safer lithium-ion batteries, Electrochim. Acta 187 (2016) 173–178. B. Massoumi, F. Abbasi, M. Jaymand, Chemical and electrochemical grafting of polythiophene onto polystyrene synthesized via ‘living’ anionic polymerization, New J. Chem. 40 (2016) 2233–2242. S.S. Kalagi, P.S. Patil, Secondary electrochemical doping level effects on polaron and bipolaron bands evolution and interband transition energy from absorbance spectra of PEDOT: PSS thin films, Synth. Met. 220 (2016) 661–666. L. Feng, K. Wang, X. Zhang, X. Sun, C. Li, X. Ge, Y. Ma, Flexible solid-state supercapacitors with enhanced performance from hierarchically graphene nanocomposite electrodes and ionic liquid incorporated gel polymer electrolyte, Adv. Funct. Mater. 28 (2018) 1704463. S. Mishra, P. Yogi, P.R. Sagdeo, R. Kumar, TiO2-Co3O4 core-shell nanorods: bifunctional role in better energy storage and electrochromism, ACS Appl. Energy Mater. 1 (2018) 790–798. S. De, T.M. Higgins, P.E. Lyons, E.M. Doherty, P.N. Nirmalraj, W.J. Blau, J.J. Boland, J.N. Coleman, Silver nanowire networks as flexible, transparent, conducting films: extremely high DC to optical conductivity ratios, ACS Nano 3 (2009) 1767–1774. F. Xu, Y. Zhu, Highly conductive and stretchable silver nanowire conductors, Adv. Mater. 24 (2012) 5117–5122. J. Kim, S.H. Lee, H. Kim, S.H. Kim, C.E. Park, 3D hollow framework silver nanowire electrodes for high-performance bottom-contact organic transistors, ACS Appl. Mater. Interfaces 7 (2015) 14272–14278.