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Printed Multi-Color High-Contrast Electrochromic Devices Bo-Han Chen, Sheng-Yuan Kao, Chih-Wei Hu, Masayoshi Higuchi, Kuo-Chuan Ho, and Ying-Chih Liao ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b08061 • Publication Date (Web): 23 Oct 2015 Downloaded from http://pubs.acs.org on October 26, 2015

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ACS Applied Materials & Interfaces

Printed Multi-Color High-Contrast Electrochromic Devices Bo-Han Chen,1 Sheng-Yuan Kao,1 Chih-Wei Hu,2 Masayoshi Higuchi,3* Kuo-Chuan Ho,1,4* Ying-Chih Liao1 * 1

Department of Chemical Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan

2

National Institute of Advanced Industrial Science and Technology (AIST), Anagahora 2266-98, Shimoshidami, Moriyama-ku, Nagoya 463-8560, Japan

3

National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan

4

Institute of Polymer Science and Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan KEYWORDS: Electrochromic devices, Inkjet Printing, Metallo-Supramolecular, Multicolor Patterning, Flexible electronics

ABSTRACT: In this study, electrochemical responses of inkjet-printed multi-colored 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, colors of the printed EC thin film patterns can be adjusted directly without pre-mixing or synthesizing new materials. The printed EC thin films *

To whom correspondence should be addressed. Phone: 886-2-3366-9688 Email: [email protected] ACS Paragon Plus Environment


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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 a great contrast with a transmittance change (∆T) of 40.1% and a high coloration efficiency of 445 cm2C-1 within a short darkening time of 2 s. The flexible ECDs also showed same darkening time of 2 s and still had a high ∆T of 30.1% under bending condition. In summary, this study demonstrated the feasibility to fabricate display devices with different color setup by all-solution process, and can be further extended to other types of displays.

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INTRODUCTION Electrochromic devices (ECDs) are systems with electrically controllable lighttransmissive or light-reflective properties, and have been widely proposed in many commercial applications, such as anti-glare rear-view mirrors,1 sunglasses,2 protective eyewear,2 and ‘smart windows’ for aircrafts or buildings.3-7 In the fabrication of ECD, electrochromic (EC) materials, which can switch colors electrochemically, are usually coated as thin films on transparent electrodes for fast color changes or rapid optical responses to electrical stimulus.8 The color change behavior of EC materials strongly depends on their intrinsic properties and thus many EC materials, such as transition metal oxides,9-13 Prussian blue and its analogues,14-18 viologens,19-23 conducting polymers,2, 24-30 and metallopolymers3135

have been synthesized to meet various color or optical requirements. Typically, EC thin

films can be prepared by various coating processes, including chemical vapor deposition12, 36, sol-gel36, RF-sputtering36, spin coating37, 38 and spray coating.37, 39, 40 However, these coating methods usually require masks to create thin film patterns and hence potentially result in enormous material wastes during the fabrication of commercial devices. To reduce material consumptions with a fast process for the fabrication of ECDs with color patterns, digital inkjet technology has been developed to print EC patterns on transparent conductive thin film.41, 42 The printed ECDs can have square pixel sizes as small as 500 µm × 500 µm, and are able to exhibit interactive color switching for image display applications.41 Besides thin film deposition, another technical challenge for ECD fabrication lies in its color adjustment. Regularly, an EC material can only absorb a specific wavelength and give a specific color with various tones depending on the voltage applied. Thus, these EC thin films can only yield monotonic color change. To produce a variety of color possibilities for EC materials, chemists have tried various chemical synthetic methods, such as side chain 3 ACS Paragon Plus Environment


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functionalization43 and copolymerization.44 Besides polymer synthesis, one can also utilize the ligand/ion interactions in coordinated polymers to synthesis EC materials with different absorption spectra. Recently, Higuchi et. al.45, 46 synthesized a new class of EC material, metallo-supramolecular polymers (MEPE), that exhibit electrochromic behavior based on the redox reaction of the inserted metal ions. Due to the metal-to-ligand change transfer (MLCT) effect of MEPE,34 the polymer materials show various colors depending on the conjugated metal ions. Consequently, by simply replacing the inserted metal ion, one can easily obtain EC materials of similar molecular structures having different colors.47 Furthermore, by mixing Fe(II) and Ru(II) ions at various ratios in the MEPE synthesis, Hu et al. obtained EC materials showing multi-electrochromism.39

These MEPEs exhibit a high transmittance

change up to 60% at 580 nm with a fast response time of a few seconds.39 Although EC materials can be synthesized to offer a variety of colors, the chemical synthesis still takes time, and thus it is of practical interests to investigate color variation by mixing EC materials. Generally, the absorbance of a binary EC mixture can be resulted from the superposition of the individual absorbance. As shown recently by Bulloch et al., mixing EC polymers with three primary colors (cyan, magenta, and yellow) in solution at various ratios can yield in thin films with predictable colors.48 However, the pre-mixing ink and spray coating would lead to material waste and inconvenience in color adjustment. To allow flexible color adjustment at low material consumption rates, inkjet printing skills with digital color adjustment method is proposed in this work to create patterned EC thin films with two primary colors as a proof-ofconcept study. Moreover, when two different metal ions are synthesized together into one polymer chain for color variation, complex electrochemical interactions occur and significantly affect the redox potentials for electrochromism.39 Thus, a thorough investigation on the electrochemical properties of inkjet-printed EC mixtures is needed and will also be


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extensively discussed in this study to identify the interactions between the molecules of the printed primary colorants. Here, a simple direct writing method is developed to investigate the feasibility of applying digital color adjustments to print EC thin film patterns. In inkjet printing process, MEPE solutions with two primary colors are printed digitally on flexible electrodes to create multi-color EC thin films. Different from any other coating methods, inkjet printing technology can produce EC films with various colors without pre-mixing or synthesizing new materials and can deliver materials at the desired location precisely without the using of masks. The electrochromic properties, such as redox potential, UV-vis absorption of the inkjet printed EC films will be studied to see whether there is any difference. Furthermore, the coloration efficiency and response time will be explored to evaluate the performance of the flexible solid-state ECDs with binary EC materials. The electrochemical stability of the fabricated ECD under bending conditions will also be demonstrated to ensure the needed darkening-bleaching cycles for flexible display applications. Finally, an ECD with multicolor patterns is also fabricated to demonstrate the ability of precise deposition via the inkjet printing process. EXPERIMENTAL Materials: Acetone, methanol, acetonitrile (ACN), lithium perchlorate (LiClO4), 4’,4””-(1,4Phenylene)-bis(2,2’:6’,2”-terpyridine) (97%), iron(II) acetate (Fe(OAc)2, >99.99%), cistetrakis(dimethylsulfoxide)dichlororuthenium(II)

(RuCl2(DMSO)4,

98%),

and

poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP, MW 400,000, pellets) were purchased

from

Sigma

Aldrich,

USA.

1-ethyl-3-methylimidazolium-

bis(trifluoromethylsulfonyl) amide (EMIBTI, 99%) was purchased from UniRegion Bio-Tech Co., Taiwan. Deionized water (Millipore Milli-Q grade) with a resistivity of 18.2 MΩ cm−1 5 ACS Paragon Plus Environment


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was used in the experiments. ITO-glass (Rsh = 6.8

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Ω/ □ ) and flexible ITO-PEN

(polyethylene-naphthalate) slides (Rsh = 35 Ω/□) were purchased from Yu-Yi Enterprise Co., Taiwan. The ITO slides (3.0 × 4.0 cm2) were cleaned by rinsing sequentially with DI water and ethanol in ultrasonic bath (DELTA DC300H), and dried in a vacuum oven. Ink preparation and printing process: The synthesis of Fe-MEPE, Ru-MEPE or Fe/RuMEPE (the molecular structures can be found in Figure S1) was achieved based on a previously published report45, 46 to form a 1.0 wt% MEPE/methanol solution. The solution was further diluted with equal volume of DI water to reduce nozzle clogging problems in inkjet printing process. The drop deposition was made by a MicroFab JetLab4 system (MicroFab Technologies Inc., USA). The printing parameters are listed in Table S1. Droplets of 70 µm were ejected from a nozzle of 50 µm in diameter at a speed of 1.01 m/s and a frequency of 500 Hz with a dot spacing of 50 µm for all printed patterns. During the printing process, the substrate was heated at 35°C. In the printing process of the color mixing thin films, the inks were placed in two cartridges and printed one after another. Electrolyte preparation: A transparent solid-state electrolyte thin film was prepared by mixing PVDF-HFP, EMIBTI, and acetone with a weight ratio of 1:4:7.49 The resulting solution was then poured into a glass petri dish and dried overnight in a vacuum oven at 70oC for 24 h. The dried thin film (with a thickness of 500 µm) was then peeled off carefully and cut into proper size for ECD fabrication. Fabrication of ECD: The printed MEPE thin films on ITO-PEN or ITO-glass were first covered by the solid-state electrolyte thin film, followed by another layer of conductive transparent thin film, as shown in Figure 1. These layers were pressed firmly by hand and the electrodes were connected to a function generator (AFG2225, Gwinstek Co., Taiwan).


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Thin film characterization: The electrochemical experiments were performed with a potentiostat (6271E, CH Instruments Inc., USA). Cyclic voltammetry (CV) was performed by submerging the printed MEPE films in 0.1 M LiClO4/ACN electrolyte. A Pt-sheet (1 cm in width and 2 cm in length) was used as the counter electrode with an Ag/Ag+ electrode as the reference, and a scan rate of 20 mV/s was used for CV measurement. The difference in the absolute potential between Ag/Ag+ electrode (Figure S2) and saturated calomel electrode (SCE)50 is 0.2588 V. The in-situ UV-vis and CIE color space experiments were performed with a light source (DH-2000-BAL) and the CHI potentiostat. The photographs were taken with a Nikon Coolpix P7700 camera under regular fluorescent lighting in office environment. The bending test was done by placing the flexible ECD of 3 cm in width into a 2 cm gap between two acrylic plates. This results in a radius of curvature of 1 cm. Ionic conductivity: The electrochemical impedance spectroscopy of the electrolyte was measured at the open-circuit voltage with a perturbation voltage of 10 mV over the frequency range from 100 kHz to 0.1 Hz using Autolab PGSTAT 30. Ionic conductivity was calculated using σ = L/RA, where R is the bulk resistance of the electrolyte obtained from Nyquist plot, L is the thickness of electrolyte between the ITO-glasses, and A is the active area of the sample (i.e., 1 cm2).

RESULTS AND DISCUSSION Color mixing and pattern formation To demonstrate the feasibility of printing multi-color thin film patterns with the least consumption of inks, the dot ratio between red Ru-MEPE and blue Fe-MEPE inks are adjusted digitally (Figure 2) to give sequential color variations from red, purple to blue. First, a series of drop arrays with different red/blue printing ratios were printed to produce squares 7 ACS Paragon Plus Environment


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of 1.0 cm2 on ITO-glass. As shown in Figure 2(a), with the same total dot density, digital adjustments of red/blue ratio can result in thin films having various colors. This result also indicates the feasibility to further applying Co-MEPE, a yellow colorant, as the third primary color to extend the color space. Since both the substrates were coated with ITO, the wetting phenomena of inks on them are similar (Figure S3). Thus, the same experimental conditions can be applied directly to both substrates. The ejection of the droplets from the nozzle is stable so that the droplets appear at the same location before and after printing (Figure S4). The optical images (Figure S5 & Figure S6) of the color mixing sample shows that the edge of droplets from two inks overlapped since the dry drop size was larger than the space between droplets. Besides color variation, one can also deliver inks at specific locations to fabricate patterned EC thin films by digital printing (Figure 2(b-c)). UV-Vis spectra are also collected to qualitatively describe the color changes of the printed EC thin films (Figure 3). Because of the MLCT effect,34 the spectra show absorption peaks at 515 nm and 580 nm for MLCT of Ru(II) and Fe(II) ions in MEPE polymers, respectively. Clearly, the peak at 515 nm due to the MLCT of Ru(II) is proportional to the quantity of Ru-MEPE ink in the fabricated EC thin films. The same phenomenon is also observed at 580 nm, where the absorbance is also proportional to the quantity of printed Fe-MEPE ink. The 1976 CIE LAB (L*a*b*) method was utilized to represent colors measured in situ of the EC film with various ratios between FeMEPE and RuMEPE. The resulting L*a*b* values are listed in Table 1. As expected, the darken states show lower L* values than that of the bleach states, and the CIE values of the bleach states locate almost in the same position near the point (0,0) which indicates highly achromatic films regardless of the FeMEPE/RuMEPE ratios. On the other hand, the values of a* and b* of the darken states change almost linearly with the ratio of FeMEPE/RuMEPE (Figure S7), showing the accurate deposition of inks over the area. These results show strong evidence to support that the physical stacking of MEPE ink droplets can 8 ACS Paragon Plus Environment

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also yield multi-color thin films with digital adjustments in printing schemes and the color depth can be tuned by controlling the printed amount of MEPE materials. Electrochemical analyses CV method is used to examine the electrochemical properties of the printed EC thin films (Figure 4). A redox pair at 771 and 718 mV (vs. Ag/Ag+) is observed at a scan rate of 20 mV s-1 for a Fe-MEPE thin film. These peaks refer to the electrochemical oxidation and reduction of Fe-MEPE respectively. Similarly, a redox pair for Ru-MEPE thin film associated with the color change can be seen at 945 and 896 mV. For printed thin films containing both FeMEPE and Ru-MEPE, two redox pairs can be observed almost at the same potentials noticed for pure Ru-MEPE and Fe-MEPE thin films (Table 2). Similar color mixing can also be achieved via synthesis process in previous study.39 As shown in Figure 4, the current densities of the redox peaks are almost linearly proportional to the corresponding amount of the primary inks. Furthermore, the redox pairs of the synthesized mixed-color polymers showed larger peak shifts in potentials in previous work. In this work, the redox peaks of color mixing samples show less potential shifts (0-15 mV) compared with those of color mixing EC thin films via synthesis process (13-27 mV).39 It is technically difficult to evaluate the molecular structural difference between the pristine Fe-MEPE/Ru-MEPE and the hybrid Fe/Ru-MEPE39 (Figure S1). Both NMR and GPC tests failed due to the ferromagnetic nature of Fe(II) and Ru(II) and broken coordination bonds in the column, respectively. One can only confirm that the polymer length of solid state Fe-MEPE is very long and more than 1 µm from AFM measurements.51 Despite lacking direct evidences in molecular structural differences, the less potential shifts in the CV results clearly indicate weaker interactions between the central Ru and Fe ions in the pristine Fe-MEPE/Ru-MEPE than in the hybrid Fe/Ru-MEPE. Because the color mixing is achieved physically by stacking ink drops instead 9 ACS Paragon Plus Environment


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of metal alternating chemical synthesis, this interaction between metal ions is intermolecular rather than intramolecular. This advantageous physical stacking characteristic can be used to control color variation by tuning the supplied voltage and will be discussed in the following section. Transmittance change and response time of the ECD The printed ECD shows attractive EC performance under either flat or bending conditions. The printed EC thin film shows a high contrast and fast switch time (Figure S8 and S9) as in previous research via spray coating method39. After assembled as an ECD, however, due to the large electrical resistance or lack of ion storage layer, a large switching time of ~ 30 s is needed for complete reaction with a higher applied voltage of 3 V (Figure S10). Figure 5 shows the transmittance changes of the fabricated devices between -3.0 and 3.0 V with a switching time interval of 50 s. Because the solid-state electrolyte has no absorption peak in the range of 400 and 800 nm (Figure S11), the color variation of the ECDs can be clearly observed. Under flat condition, the Fe-MEPE ECD shows a high contrast with a transmittance change (∆T) of 40.1% at the characteristic absorption wavelength of 580 nm. The color change can be observed visually as shown in Figure 6(a). The bleaching time (tb) and darkening time (td) can also be calculated. The values of tb and td for Fe-MEPE device at flat condition are 26 s and 2 s, respectively. The response time of the ECD is much longer than that of the EC film (cf. Figure 5 and Figure S8). The only difference between them is that different electrolytes were used. Because the conductivity of the solid-state electrolyte (1.9 mS/cm) is much lower than that (8.8 mS/cm) of the ionic liquid (0.1 M LiClO4 in ACN), the prolong response time of the fabricated ECD is expected. The electrochemical properties of the devices were also tested under bending condition with radius of curvature ~ 1.0 cm (Figure 6(b)). The total thickness of the ECD is 0.75 mm, and thus the ECD has an overall 10 ACS Paragon Plus Environment

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7.5% strain after bending. The bent ECD can still exhibit a ∆T of 30.9% with observable color contrast (Figure 6(c)) upon darkening and bleaching, showing the strong mechanical stability of the ECD. The Ru-MEPE ECD also shows similar characteristics as those of FeMEPE. The printed ECD also shows an impressive coloration efficiency, which is the extent of optical density change caused by a fixed charge/discharge amount during redox reaction of an EC material. Coloration efficiency can be calculated from the following equation: ்

ߟ = log ்್ ൗܳௗ ೎

(1)

where η (cm2 C-1) is the coloration efficiency, Tb and Tc are the bleached and colored transmittance values, respectively, and Qd is the injected/ejected charge per unit area. Figure 7 shows the charge/discharge amount for a Fe-MEPE ECD under flat and bending conditions. From the oxidation peaks (Figure 7(b)), which show the charge amount to bleach a flat ECD after switching the applied voltage from -3.0 V to 3.0 V, the value of Qd of 2.86 mC/cm2 can be obtained. Similarly, the amount of charge to darken the flat ECD can be calculated from the reduction peaks (Figure 7(c)) as 2.67 mC/cm2. The coloration efficiency can then be calculated as 445 cm2C-1 by inserting the later value into equation (1). Under bending conditions, Qd slightly increases by ~10% compared to the flat one, and therefore 2.98 mC/cm2 for bleaching and 2.88 mC/cm2 for darkening were obtained. This suggests more leakage currents were noticed in the bent ECD. In addition, bending also leads to a lower transmittance difference (30.1%, Table 3). These lead to the coloration efficiency of the bent ECD is 381 cm2C-1, which is 15% lower than that under flat condition, nevertheless, but the value is still a quite impressive for regular ECDs. The stability of the flexible solid-state device was also examined. As shown in Figure S12, the darkening state remained unchanged 11 ACS Paragon Plus Environment


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during the test, indicating the stability of the MEPE molecules. In contrast, after 400 switching cycles, the transmittance of bleach state slowly decreased to a plateau of 30% transmittance under continuous operation. This unstable bleach state shows that MEPE oxidation process cannot sustain well without a charge storage layer. Thus, to improve the long term stability of the ECD, a charge storage material with ions or radical provider52 suitable for MEPEs should be used. Multi-color ECD The printed ECD can exhibit multiple colors by manipulating the printed patterns or the applied electrical signals. First, a sample ECD with a Fe/Ru mixing ratio of 1:1 is tested. After bleached under 3.0 V (the potential as shown in the inset diagram in Figure 8(a)) for 30 s, the ECD is darkened at various reduction voltages while UV-vis absorption spectra are recorded. Because of the difference in redox potential of Fe(III) and Ru(III), the ECD shows red color initially at low applied voltages. As shown in Figure 8(a), when the applied potential decreases but higher than -0.7V, the absorption peak at 515 nm gradually increases while the absorption at 580 nm remains low. After a potential lower than -0.9 V is applied, Fe(III) in Fe-MEPE can be reduced so that the blue color starts to show up and the peak at 580 nm starts to rise. As summarized in Figure 8(b), the peak heights at 515 nm and 580 nm both reach a plateau when a potential lower than -1.2 V is applied, indicating complete reduction of both Fe(III) and Ru(III) in the ECD. Due to the high electrochemical stability of MEPE polymers, the color of the ECD becomes purple and remains its color even when a reduction voltage as low as -3.0 V is applied. Please notice that the data shown here are “voltage” between the two electrodes of an ECD assembly in Fig. 8(a). It is different from the “potentials” in the in-situ UV-vis spectral measurement of MEPE film,39 which was measured in a solution electrolyte with three electrodes system. Thus, although the CV test in Figure 4 also shows nearly the same results as in the previous study39 with a potential 12 ACS Paragon Plus Environment

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window of 0 V~1.2 V, a larger voltage was necessary to make the device work due to the internal resistance of the ECD assembly. Images of an ECD where two EC materials printed as separate patterns were also demonstrated in Figure 9. Again, the printed EC film shows the ability of precision deposition of inks in inkjet printing process. Although the two materials are coated side by side rather than on top of each other, the redox potentials of them remain unchanged comparing to the color mixing sample. Since the blue Fe-MEPE can be oxidized more easily than the red Ru-MEPE as discussed previously, the blue pattern can be bleached with red surrounding pattern unchanged at 1.7 V. To completely bleach the ECD, a voltage of 3.0 V is required. When recovering the color patterns, the red one still shows a faster response at low voltages and both colors are recovered at -3.0V. Moreover, the ECD shows great mechanical stability and exhibits the same color display even under bending conditions (Figure 9(b)).

CONCLUSIONS An inkjet printing method is developed to fabricate electrochromic thin film patterns with various colors by adjusting digital printing schemes. As a proof-of-concept study, two MEPE electrochromic materials with different centric metallic ligands are printed on transparent conductive sheets to form electrochromic devices. The ECDs show a great contrast with a transmittance difference (∆T) of 40.1%, and a high coloration efficiency of 445 cm2C-1 with a response time of 2 s. With a solid electrolyte, the ECDs can be bent and show nearly the same response times and color changes as those without bending. With the advantages of inkjet printing process, print patterns with multiple colors with excellent precision can be achieved. Herein, by tuning the dot ratios between Ru-MEME and Fe-MEPE inks, one can physically mix the red and blue colorants, and create a series of color gradient transition from red to blue. Besides, the EC materials can also be printed easily at precise locations to create patterns 13 ACS Paragon Plus Environment


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with multiple colors. In summary, this study shows the feasibility of applying inkjet printing technology to fabricate EC thin films with specific colors and patterns, and the fabrication process can be further extended to create flexible multi-color ECD for potential display applications.

AUTHOR INFORMATION Corresponding Author E-mail: [email protected].

ACKNOWLEDGMENT The authors are grateful for the funding supports from the Ministry of Science and Technology (MOST) of Taiwan and SMART center at National Taiwan University.

SUPPORTING INFORMATION Printing parameters, chemical structures, and the associated electrochromic data of MEPE. This information is available free of charge via the Internet at http://pubs.acs.org/.

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Costa, C.; Pinheiro, C.; Henriques, I.; Laia, C. A. Inkjet Printing of Sol-Gel Synthesized Hydrated Tungsten Oxide Nanoparticles for Flexible Electrochromic Devices. ACS Appl. Mater. Interfaces 2012, 4, 1330-1340. Beverina, L.; Pagani, G. A.; Sassi, M. Multichromophoric Electrochromic Polymers: Colour Tuning of Conjugated Polymers through the Side Chain Functionalization Approach. Chem Commun (Camb) 2014, 50, 5413-5430. Alamer, F. A.; Otley, M. T.; Ding, Y.; Sotzing, G. A. Solid-State High-Throughput Screening for Color Tuning of Electrochromic Polymers. Adv. Mater. 2013, 25, 62566260. Han, F. S.; Higuchi, M.; Kurth, D. G. Metallosupramolecular Polyelectrolytes SelfAssembled from Various Pyridine Ring-Substituted Bisterpyridines and Metal Ions: Photophysical, Electrochemical, and Electrochromic Properties. J. Am. Chem. Soc. 2008, 130, 2073-2081. Higuchi, M. Electrochromic Organic–Metallic Hybrid Polymers: Fundamentals and Device Applications. Polym. J. 2009, 41, 511-520. Tieke, B. Coordinative Supramolecular Assembly of Electrochromic Thin Films. Curr. Opin. Colloid In 2011, 16, 499-507. Bulloch, R. H.; Kerszulis, J. A.; Dyer, A. L.; Reynolds, J. R. An Electrochromic Painter's Palette: Color Mixing Via Solution Co-Processing. ACS Appl. Mater. Interfaces 2015, 7, 1406-1412. Lee, K. H.; Kang, M. S.; Zhang, S. P.; Gu, Y. Y.; Lodge, T. P.; Frisbie, C. D. "Cut and Stick" Rubbery Ion Gels as High Capacitance Gate Dielectrics. Adv. Mater. 2012, 24, 4457-4462. Connelly, N. G.; Geiger, W. E. Chemical Redox Agents for Organometallic Chemistry. Chem. Rev. 1996, 96, 877-910. Ikeda, T.; Higuchi, M.; Kurth, D. G. Synthesis of Tetrathiafulvalene-FunctionAnalyzed Organic-Metal Hybrid Polymer. Trans. Mater. Res. Soc. Jpn 2008, 33, 403405. Hu, C. W.; Lee, K. M.; Vittal, R.; Yang, D. J.; Ho, K. C. A High Contrast Hybrid Electrochromic Device Containing Pedot, Heptyl Viologen, and Radical Provider Tempo. J. Electrochem. Soc. 2010, 157, 75-78.



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Page 18 of 31

Figure Caption

Figure 1 Schematic diagram of the experimental steps involved in the study. Figure 2 (a) Color mixing scheme and (b) resulting EC material thin films with different mixing ratio of RuMEPE to FeMEPE. (c) Multi-color patterns of EC material thin films. Figure 3 In situ UV-vis spectra of color mixing ECM thin films deposition on ITO-glass. Figure 4 Cyclic voltammograms of the color mixing ECM thin films in 0.1M LiClO4/ACN with a scan rate of 20 mV s-1. Figure 5 Transmittance change (∆T, %) (a) at 580 nm of the Fe-MEPE ECD, and (b) at 515 nm of the Ru-MEPE ECD. Figure 6 Color change between -3.0 and 3.0 V of Fe-MEPE ECD at flat condition. (b) The flexible ECD was bent with a radius of curvature of 1 cm, and (c) shows color change under applied voltage. Figure 7 (a) Current change in Fe-MEPE ECD when switching between -3.0 and 3.0 V under two different conditions. (b) Enlarge part of oxidation peaks and the discharge amount of bleaching. (c) Enlarge part of reduction peaks and the charge amount of darkening. Figure 8 (a) In situ UV-vis spectra of the printed a bleached ECD after applying various reduction potentials. The ECD sample was printed with a 1:1 Fe/Ru ratio. (b) Variation of peak absorbance with applied potential for the printed ECD sample. Figure 9 Color states of printed multi-color patterning flexible ECD at different applied potentials under (a) flat and (b) bending conditions. 18 ACS Paragon Plus Environment

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Figure 1



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Page 20 of 31

Figure 2


Page 21 of 31

Figure 3

0.4 Ru 5

Absorbance (-)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 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 53 54 55 56 57 58 59 60


0.3

1 2 3 4 5

Fe

4

Fe:Ru 4:0 3:1 2:2 1:3 0:4

3

0.2 2

0.1 400

1

500

600

700

800

Wavelength (nm)



Figure 4

0.15 2

Current Density (mA/cm )

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Page 22 of 31

0.10 0.05

1 2 3 4 5

1

Fe:Ru 4:0 3:1 2:2 1:3 0:4

2 3 4 5

0.00 -0.05 -0.10 -0.15

Scan rate : 20 mV/s MEPE/ITO-glass Electrolyte : 0.1M LiClO4/ACN

0.0

0.2

0.4

0.6

0.8

1.0

1.2

+

Potential (V vs. Ag/Ag )


Page 23 of 31

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Figure 5



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Figure 6


Page 25 of 31

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Figure 7



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Page 26 of 31

Figure 8

s


Page 27 of 31

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Figure 9

(a)

(b)



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Page 28 of 31

Table Caption

Table 1 The CIE color space of the color mixing EC thin films. Table 2 Oxidative and reductive peak potentials of color mixing thin films Table 3 The EC properties of single color flexible ECDs


Page 29 of 31

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Table 1 The CIE color space of the color mixing EC thin films. Fe:Ru Color State Darken

Bleach

4:0

3:1

2:2

1:3

0:4

L* = 84.1 a* = 6.5 b* = -14.0 L* = 95.7 a* = -1.1 b* = 1.5

L* = 83.4 a* = 10.1 b* = -9.6 L* = 95.2 a* = -2.2 b* = 1.9

L* = 85.4 a* = 12.1 b* = -2.4 L* = 94.7 a* = -2.4 b* = 2.5

L* = 87.2 a* = 14.1 b*= 6.5 L* = 94.8 a* = -2.2 b* = 3.2

L* = 90.7 a* = 15.2 b* = 12.4 L* = 94.9 a* = -2.5 b* = 3.3



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Table 2 Oxidative and reductive peak potentials for the pure and mixing thin films Eox of

Ered of

Eox of

Ered of

Fe2+(mV)

Fe2+(mV)

Ru2+(mV)

Ru2+(mV)

FeMEPE

771

718

－

－

Fe/Ru = 3:1

777

718

931

899

Fe/Ru = 2:2

778

719

936

898

Fe/Ru = 1:3

780

719

940

895

RuMEPE

－

－

945

896


Page 31 of 31

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Table 3 The EC properties of single color flexible ECDs* Device

Max

Darkening

Bleaching

Transmittance

Charge/discharge

wavelength

time

time

change

amount

change

Coloration efficiency

-2

(td, s)

(tb, s)

(∆T, %)

(Q, mC cm )

(λmax, nm)

(η, cm2 C-1)

FeMEPE

580

2.0

26

40.1

2.67/2.86

445

Fe Bending

580

2.0

21

30.1

2.88/2.98

381

RuMEPE

515

0.5

27

32.3

2.10/2.77

521

Ru Bending

515

2.0

21

29.9

2.46/2.83

439

*

The color of the printed ECD was switched between -3.0 and 3.0 V with a time interval of 50 s.


Printed Multicolor High-Contrast Electrochromic Devices - ACS

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