Electrostatic-Force-Assisted Dispensing Printing of ... - ACS Publications

Subscriber access provided by CORNELL UNIVERSITY LIBRARY

Article

Electrostatic-Force-Assisted Dispensing Printing of Electrochromic Gels for Low-Voltage Displays Keon-Woo Kim, Hwan Oh, Jaehyun Bae, Haekyoung Kim, Hong Chul Moon, and Se Hyun Kim ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 04 May 2017 Downloaded from http://pubs.acs.org on May 9, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 24

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

ACS Applied Materials & Interfaces

Electrostatic-Force-Assisted Dispensing Printing of Electrochromic Gels for Low-Voltage Displays Keon-Woo Kim,a,† Hwan Oh,b,† Jae Hyun Bae,c,d Haekyoung Kim,e,* Hong Chul Moon,b,* and Se Hyun Kima,c,f,*

a

Department of Nano, Medical, and Polymer Materials, Yeungnam University, Gyeongsan,

North Gyeongsang 38541, Republic of Korea b

c

Department of Chemical Engineering, University of Seoul, Seoul 02504, Republic of Korea

Department of Advanced Organic Materials Engineering, Yeungnam University, Gyeongsan,

38541, Republic of Korea d

Korea Dyeing Technology Institution (DYETEC), Daegu 41706, Republic of Korea.

e

School of Materials Science and Engineering, Yeungnam University, Gyeongsan, 38541,

Republic of Korea f

School of Chemical Engineering, Yeungnam University, Gyeongsan, North Gyeongsang 38541,

Republic of Korea †

These authors equally contributed to this work.

*Corresponding authors. E-mail: [email protected] (H.K.), [email protected] (H.C.M.), [email protected] (S.H.K.) Keywords: Electrochromism, Electrochemical Displays, Ion Gels, Printed Electronics, LowVoltage Devices, Electrohydrodynamic Printing

ACS Paragon Plus Environment

1


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

Page 2 of 24

ABSTRACT

In this study, low-voltage, printed, ion gel-based electrochromic devices (ECDs) were successfully fabricated. While conventional dispensing printing provides irregularly printed electrochromic (EC) gels, we improved the adhesion between the printed gel and the substrate by applying an external voltage. This is called electrostatic-force-assisted dispensing printing. As a result, we obtained well defined, printed, EC gels on substrates such as indium tin oxide (ITO)coated glass. We fabricated a gel-based ECD by simply sandwiching the printed EC gel between two transparent electrodes. The resulting ECD, which required a low coloration voltage (~0.6 V), exhibited a high coloration efficiency (η) of 161 cm2/C and a large transmittance contrast (~82%) between the bleached and colored states at −0.7 V. In addition, electrostatic-force-assisted dispensing printing was utilized to fabricate directly patterned ECDs.


2

Page 3 of 24

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


INTRODUCTION Electrochromic devices (ECDs), which can alter optical properties depending on the applied voltage, are an attractive class of displays for printed electronics because of their low-voltage operation, simple device configuration, and easy fabrication process on flexible substrates.1–13 In these devices, in addition to the cathode and anode, an electrolyte layer on which electrochemical reactions occur is an essential component. The simplest electrolyte form is an aqueous solution containing salts, but the relatively narrow electrochemical window (approximately ±1 V) of water limits the range of applied voltages.14 Thus, other electrochemically stable organic solutions (e.g., a propylene carbonate (PC) solution) have been employed in liquid-based ECDs.12 Although these solutions have excellent ionic conductivities, liquid electrolytes have disadvantages, such as poor mechanical properties and leakage issues.14 This implies that solidstate electrolytes must be utilized for flexible or stretchable devices. However, conventional polymer electrolytes, such as Li salt-containing polyethylene oxide (PEO), are unsuitable for device applications because of impeded ionic motion (i.e., low ionic conductivity).15 To obtain solid-state electrolytes with good ionic conductivities and mechanical properties, ion gels composed of ABA-triblock copolymers and room temperature ionic liquids have been developed and applied to electrochemical displays (e.g., electrochemiluminescence (ECL) devices and ECDs).5,6,16-19 Patterning is an essential requirement for allowing displays to convey information. In the past, photolithography has been utilized to prepare patterned insulating photoresists on indium tin oxide (ITO)-coated substrates.5,6 As a result, most electrode surfaces were covered by negative photoresists and selected areas were exposed, on which either light emission or coloration occurred. Photolithography demands a photomask and multiple fabrication steps.


3


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

Page 4 of 24

Thus, direct printing of gels is likely to be more efficient. Several printing methods, including digital printing and transfer printing, have been considered as low-cost simple fabrication techniques for patterning.20-22 In particular, digital printing methods (e.g., ink jet, aerosol jet, and electrohydrodynamic (EHD) jet methods) can create a pattern directly on a substrate through the movement of nozzles controlled by a computer.21-27 In particular, EHD jet printing is known to produce a fine jet stream of ink droplets using an electric field applied between a nozzle tip and a substrate. This method makes it possible to realize high-resolution patterning with positioning accuracy and good adhesion of ink materials to the substrate for several applications, including the deposition of thin films, direct writing, spray formation, and the encapsulation and fabrication of pharmaceutical particles.27-29 It is worth noting that fine line stability has been regarded as one of the critical issues in nonlithographic methods (including digital printing) with respect to achieving good pattern fidelity.30,31 The stability of the printed line has been achieved through control of the surface tension at the liquid/solid interface and the introduction of a specific building block (e.g., bank structure).32-35 Hence, additional steps have been necessary to control the printed pattern. In this study, electrostatic force-assisted dispensing printing of EC gels via the dripping mode of EHD printing was used to fabricate ECDs, improving the adhesion and dimensional stability of the printed EC gel without any additional steps. We applied an external voltage between the printer nozzle and the substrate (i.e., transparent electrodes), by which positively charged species in the gel were positioned at the gel surface. As a result, the printed gel could electrostatically interact with the negatively charged substrate, and well-defined printed EC gel patterns were obtained. In addition, the line width of the printed gel was tuned by simply changing the flow rate. ECDs were fabricated by sandwiching the printed gel, containing ethyl viologen (EV2+) and dimethyl


4

Page 5 of 24

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


ferrocene (dmFc), between two transparent electrodes. While the device was slightly yellowish in the bleached state because of dissolved anodic species (dmFc), the reduction of EV2+ at −0.6 V resulted in a blue-colored state. In addition, the ECD exhibited a good coloration efficiency (η) of ~161 cm2/C at −0.7 V. To demonstrate the advantages of direct electrostatic-force-assisted dispensing printing of EC gels, pre-designed EC gels were printed and employed, resulting in patterned ECDs that showed distinct EC behaviors (bleaching and coloration). Experimental Section Materials: All of the materials were purchased from Sigma-Aldrich except ethyl viologen bis(hexafluorophosphate) [EV(PF6)2], which was prepared using an anion exchange reaction between ethyl viologen dibromide (EVBr2) and an excess amount of ammonium hexafluorophosphate (NH4PF6). To prepare the EC gel ink for printing, EV(PF6)2, dmFc, poly(vinylidene

fluoride-co-hexafluoropropylene)

[P(VDF-co-HFP)],

and

1-ethyl-3-

methylimidazolium bis(trifluoromethylsulfonyl)imide [EMI][TFSI] in a predetermined weight ratio of 1:0.44:1:10 were dissolved in acetone. The chemical structures of all materials used here are shown in Figure 1.


5


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

Page 6 of 24

Figure 1. Schematic illustration of the electrostatic force-assisted dispensing printing and printed EC gel composed of EV(PF6)2, dmFc, P(VDF-co-HFP), [EMI][TFSI] with a weight ratio of 1:0.44:1:10.


6

Page 7 of 24

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


Printing electrochromic ion gel: To obtain uniform printed ion gels using an electrostaticforce-assisted dispensing printer (Enjet, Korea), a 100 µL syringe was filled with the EC gel solution and connected to a ceramic nozzle holder (outer diameter: 200 µm). Then, the solution was ejected through the nozzle onto the ITO-coated glass at various flow rates from 0.7 to 1.2 µL/min, where the flow rate was controlled by a motorized pump. The printing velocity and distance between the nozzle and substrate were adjusted using a motorized stage with x and y axes. To provide a good electrostatic interaction, an electric field was applied between the nozzle and the substrate. In this work, we used optimized applied voltage, working height, and printing velocity values of 0.3 kV, 5 µm, and 0.6 mm/s, respectively. The entire process was monitored using a CCD camera (Enjet, Korea) (Figure 1). Device fabrication and characterization: The printed EC gel was annealed at 70 °C for 30 min, followed by the placement of a counter ITO-coated glass on the gel. Variations in the absorption and transmittance spectra were recorded on a UV-vis spectrometer (GENESYS™ 10S, Thermo Fisher Scientific). A cyclic voltammogram of the EC gel was obtained using a potentiostat (Weis 500, WonA Tech.) at a scan rate of 20 mV/s, in which the working, counter, and reference electrodes were a Pt disk, an ITO-coated glass, and a Ag wire, respectively, and dmFc was used as an internal standard. The voltage applied in this work was supplied by a potentiostat.

Results and Discussion EHD printing results in several jetting modes that are categorized by the shape of the meniscus of the ink drop, which depends on the applied electric field. The categories, as shown in Figure S1 in the Supporting Information are as follows: dripping, micro-dripping, cone-jet,


7


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

Page 8 of 24

and multi-jet modes. Without applied electric fields or with a weak electrostatic field, it is not possible to deform the meniscus of the ink drop hanging on the nozzle tip (Figure S1a), which is referred to as the dripping mode. As the electrostatic field becomes more intense, the meniscus is deformed from an ellipsoidal (microdripping, Figure S1b) to a conical shape (cone-jet, Figure S1c). The electrostatic force in the direction of the counter electrode (substrate) allows charges in the ink drop to move toward the electrode surface. As a result, the meniscus of an ink drop is elongated in the direction of the field lines, and a droplet or jet from the cone apex is generated. The application of a stronger electrostatic field irregularly creates several cones on the ink drop surface that eject jet streams (multi-jet, Figure S1d) in order to minimize their energies by rearranging the excessive accumulation of charges to a large area.36 The cone-jet mode results in the ejection of a stable and continuous ultrathin jet stream from the conical meniscus, by which a sub-micrometer-scale line width can be achieved.29,37 For our EC gel ink containing ionic liquids, however, a stable cone-jet mode is hard to maintain because a large number of ions in the EC gel ink may perturb the fluidic behavior, inducing an unstable conical meniscus for the ink drop (Figure S2). As a result, the printed film showed a scattered morphology instead of a dimensionally stable one. (Figure S3) To avoid this jetting issue, we employed a dripping mode for the EHD printing.


8

Page 9 of 24

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


Figure 2. (a) Schematic illustration of the detailed procedure for electrostatic force-assisted dispensing printing and (b) photograph of the actual printing process.

First, a nozzle tip was moved close to the substrate with a gap of less than 10 µm, as shown in the left image of Figure 2a and Figure S4a. Second, EC gel ink was ejected from the nozzle tip with an external syringe pump to make a jet column between the nozzle tip and substrate, which allows a “liquid bridge of ink” between the two that can act as the supply path for ink under the electrostatic field (middle image of Figure 2a). A pattern can be formed by dragging the nozzle while applying a bias of 0.3 kV, which is referred to as electrostatic-force-assisted dispensing printing (right image of Figure 2a and Figure S4b). The actual printing process for the EC gel ink is pictured in Figure 2b.


9


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

Page 10 of 24

Figure 3. Schematic illustrations (a and c) and optical microscopy (OM) images (b and d) of EC gels printed by conventional dispensing printing and electrostatic-force-assisted dispensing printing, respectively, where the flow rate from the nozzle was 0.7 µL/min. Inset of Figure 3c depicts dominant charges near the inside of the nozzle and the surface of printed EC gels.


10

Page 11 of 24

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


Figure 4. (a) Plot of flow rate versus line width and (b) optical microscopy (OM) images of printed EC gels at conditions in (a).

It is interesting to examine the effect of the electrostatic field on the EC gel printing process. Unless an electrostatic field was applied to the sample, this process was very similar to conventional dispensing printing. Figure 3a shows a schematic picture of conventional


11


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

Page 12 of 24

dispensing printing, in which the printer simply drops the EC gel ink on a substrate such as a ITO-coated glass substrate without any bias. Because there is no specific interaction between the EC gel and the ITO-coated glass, the printed EC gel cannot firmly adhere to the electrode. As a result, an irregularly printed EC gel is obtained, as shown in Figure 3b. On the other hand, when we applied a positive bias at the nozzle, cations such as [EMI]+ were pushed out from the nozzle to the meniscus (see Figure 3c). As a result, a positively charged EC gel surface was induced. Thus, the printed EC gel could be pinned on the negatively charged electrode by an electrostatically favorable interaction, producing a well-defined printed EC gel pattern (see Figure 3d). The line width of the printed EC gel was plotted as a function of the flow rate, which had a range of 0.7–1.2 µL/min (Figure 4a). It should be noted that when the flow rate was less than 0.7 µL/min, a continuous EC gel pattern was rarely obtained. When the flow rate was 0.7 µL/min, the corresponding line width was 258 µm. The printed line width was linearly proportional to the flow rate. This result was quite predictable, because a larger amount of the EC gel ink was provided when printing at the higher flow rate. The OM images clearly show the dependence of the line width on the flow rate (Figure 4b). To estimate the redox potential of EV2+ in the printed EC gel, a cyclic voltammogram (CV) was recorded (Figure 5a). The printed EC gel successfully served as an electrolyte (medium) for redox reactions, and the redox potential of EV+•/EV2+ was determined to be −0.75 V (vs. dmFc+/dmFc). If we consider the difference in the onset potentials for the reduction of EV2+ (approximately −0.67 V vs. dmFc+/dmFc) and the oxidation of dmFc (approximately −0.07 V vs. dmFc+/dmFc), the overall redox reactions (i.e., coloration) began upon the application of −0.6 V, which was supported by UV-vis spectroscopy. Figure 5b displays the variation of the UV-vis absorption spectra at various applied voltages. At voltages less than −0.6 V, there was no


12

Page 13 of 24

significant absorption, except a broad peak at ~440 nm due to dissolved dmFc. At −0.6 V, characteristic peaks at ~550 nm and 603 nm appeared, as expected from the CV experiment. As the applied voltage increased, the absorption by the produced EV+• species also intensified. This behavior was in good agreement with that of gel-based ECDs using drop-cast EC gels.

Current (µA)

(a)

400

EV•+

EV2+ −0.75 V

200

0

-200

dmFc+

dmFc

-400 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6

Potential (V) vs dmFc+/dmFc

(b) Absorbance (AU)

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


0.0 V −0.5 V −0.6 V

3

−0.7 V −0.8 V

2

1

0 400

500

600

700

800

Wavelength (nm)

Figure 5. (a) Cyclic voltammogram of the printed EC gel containing both EV2+ and dmFc, in which a potential scan rate was 20 mV/s, and the working, counter, and reference electrodes were a Pt disk, ITO-coated glass, and Ag wire, respectively. (b) Dependence of UV-Vis spectra on the applied voltage.


13


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

Page 14 of 24

Figure 6 shows the device kinetics during coloration and bleaching. At –0.6 V, the time (∆t90%) required for a 90% change in the maximum transmittance contrast was ~16 s, and the maximum transmittance contrast (∆Tmax) was ~56% (Figure 6a). A faster coloration behavior (∆t90% ~ 10.8 s) was observed at –0.7 V. This result may be attributed to more efficient charge transfer from the electrode to the redox couples at a higher voltage. In addition, a larger ∆Tmax of ~82% was observed as a result of the larger injected charge (Figure 6b). In contrast, under a short-circuit condition, the ∆t90% (~12.4 s) value for bleaching after coloration at −0.6 V was quicker than that at −0.7 V (~22.4 s), as seen in Figure 6c and 6d. It should be noted that there were two pathways for bleaching: the direct oxidation of EV+• at the electrode and an electron transfer reaction between EV+• and dmFc+ in the middle of the gel. A higher concentration of EV+• was expected in the coloration at –0.7 V. According to the resulting concentration gradient, EV+• diffused further from the cathode during coloration at –0.7 V, and the thickness of the layer that contained EV+• was larger than at −0.6 V. The EV+• near the electrode could be readily oxidized to EV2+. However, the EV+• species demanded a longer time overall because a relatively slow diffusion was related to the bleaching. This process could explain the longer bleaching time at –0.7 V.


14

(a) Transmittance (%)

100

-0.6 V

(b)

80 60 40 20

100

0

80 60 40 20 0

0

10

20

30

40

50

60

0

10

20

Time (s)

30

40

50

60

50

60

Time (s)

(d)

100 80 60 40 20 0

100

Transmittance (%)

(c)

Transmittance (%)

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


Transmittance (%)

Page 15 of 24

80 60 40 20 0

0

10

20

30

40

50

60

0

10

20

Time (s)

30

40

Time (s)

Figure 6. Transient transmittance profiles at 550 nm during coloration at (a) −0.6 V and (b) −0.7 V, respectively, followed by bleaching under short circuit ((c) and (d)).


15


(a)

0.5

∆OD

0.4 0.3 0.2 0.1

Coloration Efficiency at −0.6 V = 122 cm2/mC

0.0 0

2

4

6

8

10

Charge Density

(b)

12

14

16

(mC/cm2)

1.0 0.8

∆OD

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

Page 16 of 24

0.6 0.4 0.2

Coloration Efficiency at −0.7 V = 161 cm2/mC

0.0 0

3

6

9

12

Charge Density

15

18

21

(mC/cm2)

Figure 7. Variation of ∆OD as a function of injected charge density, in which the slope of linear fit corresponds to coloration efficiency at (a) −0.6 V and (b) −0.7 V. The ∆OD was recorded at 550 nm.

To estimate the device performance, the coloration efficiency (η) was also calculated using η = ∆OD⁄∆Q = log (Tb /Tc )⁄∆Q , where ∆OD, ∆Q, Tb, and Tc are the variation of the optical density, amount of injected charge needed to induce the corresponding ∆OD, transmittance at the bleached state, and transmittance at the colored state, respectively. The dependence of the optical


16

Page 17 of 24

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


density (OD) on the charge density at −0.6 V and −0.7 V is provided in Figure 7a and 7b, respectively. The slope of the line fitted in the linear regime corresponded to η. While η was 122 cm2/C at −0.6 V, a higher efficiency of 161 cm2/C was obtained at −0.7 V. This result was in good agreement with the device kinetics for the smaller ∆t90% and the larger ∆Tmax for coloration at −0.7 V. In addition, we examined the operational stability of the printed ECD during the coloration and bleaching cycles. The applied square wave was composed of two periods: −0.7 V for 6 s (coloration) and 0.0 V for 20 s (bleaching). The variation of the transmittance at 550 nm was recorded as a function of time (Figure 8). A ~37 % decrease in ∆Tmax compared to the initial ∆Tmax (~46 %) was observed after 24 h. The device still showed distinct colored and bleached states, although the test was conducted in air without specific encapsulation.

Figure 8. Operational stability test during coloration and bleaching cycles


17


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

Page 18 of 24

To take advantage of direct printing, we fabricated ECDs using EC gel patterns prepared with electrostatic-force-assisted dispensing printing. The ECD shown in Figure 9a includes connected gel lines separated by a 3 mm gap. A pattern with a smaller feature size (1 mm gap) was also successfully demonstrated (Figure 9b). Reversible EC behavior was observed in both ECDs. In addition, we fabricated ECDs that provided information using 5 mm × 6 mm printed letters (Figure 9c), indicating the potential for use as printed displays.


18

Page 19 of 24

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


Figure 9. Photographs of bleached and colored states of ECDs using EC gels printed by electrostatic force-assisted dispensing printing with various shapes: (a,b) connected lines and (c) letters. All images of colored states were captured upon application of −0.8 V.

Conclusions In this study, we printed well-defined ion gel patterns using electrostatic-force-assisted dispensing printing, demonstrating a favorable interaction between the ion gel and substrate. An EC gel solution containing EV2+ and dmFc was employed as the ink. The printed EC gel patterns were inserted between two transparent electrodes to fabricate ECDs. The resulting devices showed a good coloration efficiency of 161 cm2/C and large transmittance variation (~82%) between the bleached and colored states. In addition, we successfully demonstrated ECDs using EC gel patterns printed with various shapes (connected lines and letters). These results showed that printed gel-based ECDs can be attractive components of information displays for printed electronics.

Acknowledgments This work was supported by the Creative Economy Leading Technology Development Program through the Gyeongsangbuk-Do and Gyeongbuk Science & Technology Promotion Center of Korea (SF315012A). This research was also supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (NRF-2015R1C1A2A01053066 and 2016R1C1B2006296).

Supporting Information Available. Photographs of the various jetting modes of EHD printing, unstable meniscuses of EC gel ink in the cone-jet mode, and the scattered EC gel morphology


19


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

Page 20 of 24

induced by unstable cone-jet mode of EHD printing, the detailed images of electrostatic-forceassisted dispensing printing. These materials are available free of charge via the Internet at http://pubs.acs.org.

References (1) Monk, P. M. S.; Mortimer, R. J.; Rosseinsky, D. R. Electrochromism and Electrochromic Devices, Cambridge University Press, Cambridge, UK 2007. (2) Monk, P. M. S. The Viologens: Physicochemical Properties, Synthesis, and Applications of the Salts of 4,4′-Bipyridine , Wiley, Chichester, England 1998. (3) Rosseinsky, D. R.; Mortimer, R. J. Electrochromic Systems and the Prospects for Devices. Adv. Mater. 2001, 13, 783-793. (4) Thakur, V. K.; Ding, G.; Ma, J.; Lee, P. S.; Lu, X. Hybrid Materials and Polymer Electrolytes for Electrochromic Device Applications. Adv. Mater. 2012, 24, 4071-4096. (5) Moon, H. C.; Lodge, T. P.; Frisbie, C. D. Solution Processable, Electrochromic Ion Gels for Sub-1 V, Flexible Displays on Plastic. Chem. Mater. 2015, 27, 1420–1425. (6) Moon, H. C.; Kim, C. –H.; Lodge, T. P.; Frisbie, C. D. Multicolored, Low-Power, Flexible Electrochromic Devices Based on Ion Gels. ACS Appl. Mater. Interfaces 2016, 8, 6252–6260. (7) Jensen, J.; Krebs, F. C. From the Bottom Up – Flexible Solid State Electrochromic Devices. Adv. Mater. 2014, 26, 7231–7234. (8) Jensen, J.; Hösel, M.; Kim, I.; Yu, J. -S.; Jo, J.; Krebs, F. C. Fast Switching ITO Free Electrochromic Devices. Adv. Funct. Mater. 2014, 24, 1228–1233. (9) 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


20

Page 21 of 24

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


(10) Österholm, A. M.; Shen, D. E.; Kerszulis, J. A.; Bulloch, R. H.; Kuepfert, M.; Dyer, A. L.; Reynolds, J. R. Four Shades of Brown: Tuning of Electrochromic Polymer Blends Toward HighContrast Eyewear. ACS Appl. Mater. Interfaces 2015, 7, 1413–1421. (11) Kao, S. –Y.; Lu, H. –C.; Kung, C. –W.; Chen, H. –W.; Chang, T. –H.; Ho, K. –C. Thermally Cured Dual Functional Viologen-Based All-in-One Electrochromic Devices with Panchromatic Modulation. ACS Appl. Mater. Interfaces 2016, 8, 4175–4184. (12) Bressers, P. M. M. C; Meulenkamp. E. A. The Electrochromic Behavior of Indium Tin Oxide in Propylene Carbonate Solutions. J. Electrochem. Soc. 1998, 145, 7. (13) Barbosa. P. C.; Silva. M. M.; Smith. M. J.; Goncalves. A.; Fortunato. E. Studies of SolidState Electrochromic Devices Based on PEO/Siliceous Hybrids Doped with Lithium Perchlorate. Eletrochimica. Acta 2007, 52, 2938-2943. (14) Frackowiak, E.; Beguin, F. Carbon Materials for the Electrochemical Storage of Energy in Capacitors. Carbon 2001, 39, 937-950. (15) Yan, X.; Peng, B.; Hu, B.; Chen. Q. PEO-urea-LITFSI Ternary Complex as Solid Polymer Electrolytes. Polymer 2016, 99, 44-48. (16) Itoh, N. Electrochemical Light-Emitting Gel Made by Using an Ionic Liquid as the Electrolyte. J. Electrochem. Soc. 2009, 156, J37–J40. (17) Itoh, N. Electrochemical Light-Emitting Gel. Materials 2010, 3, 3729–3739. (18) Hong, K.; Kim, M. –G.; Yang, H. M.; Lim, D. C.; Lee, J. Y.; Kim, S. J.; Lee, I.; Lee, K. H.; Lee, J. –L. Solid-State Dual Function Electrochemical Devices: Energy Storage and LightEmitting Applications. Adv. Energy. Mater. 2016, 6, 1600651. (19) Richter, M. M. Electrochemiluminescence (ECL). Chem. Rev. 2004, 104, 3003-3036.


21


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

Page 22 of 24

(20) Lee, K. H.; Zhang, S. P.; Gu, Y. Y.; Lodge, T. P.; Frisbie, C. D. Transfer Printing of Thermoeversible Ion Gels for Flexible Electronics. ACS Appl. Mater. Interfaces 2013, 5, 95229527. (21) Ha, M. J.; Xia, Y.; Green, A. A.; Zhang, W.; Renn, M. J.; Kim, C. H.; Hersam, M. C.; Frisbie, C. D. Printed, Sub-3V Digital Circuits on Plastic from Aqueous Carbon Nanotube Inks. ACS Nano. 2010, 4, 4388-4395. (22) Gamerith, S.; Klug, A.; Scheiber, H.; Scherf, U.; Moderegger, E.; List, E. J. W. Direct InkJet Printing of Ag-Cu Nanoparticle and Ag-Precursor Based Electrodes for OFET Applications. Adv. Funct. Mater. 2007, 17, 3111-3118. (23) Mahajan, A.; Frisbie, C. D.; Francis, L. F. Optimization of Aerosol Jet Printing for HighResolution, High-Aspect Ration Silver Lines. ACS Appl. Mater. Interfaces 2013, 5, 4856-4864. (24) Sirringhaus, H.; Kawase, T.; Friend, R. H.; Shimoda, T.; Inbasekaran, M.; Wu, W.; Woo, E. P. High-Resolution Inkjet Printing of All-Polymer Transistor Circuits. Science 2000, 290, 21232126. (25) De Gans, B. J.; Duineveld, P. C.; Schubert, U. S. Inkjet Printing of Polymers: State of the Art and Future Developments. Adv. Mater. 2004, 16, 203-213. (26) Cai, G. F.; Darmawan, P.; Cui, M. Q.; Chen, J. W.; Wang, X.; Eh, A. L. S.; Magdassi, S.; Lee, P. S. Inkjet-Printed All Solid-State Electrochromic Devices Based on NiO/WO3 Nanoparticle Complementary Electrodes. Nanoscale. 2016, 8, 348-357. (27) Huang, Y. A.; Bu, N. B.; Duan, Y. Q.; Pan, Y. Q.; Lin, H. M.; Yin, Z. P.; Xiong, Y. L. Electrohydrodynamic Direct-Writing. Nanoscale. 2013, 5, 12007-12017. (28) Min, S. Y.; Kim, T. S.; Kim, B. J.; Cho, H.; Noh, Y. Y.; Yang, H.; Cho, J. H.; Lee, T. W. Large-Scale Organic Nanowire Lithography and Electronics. Nat. Commun. 2013, 4, 1773.


22

Page 23 of 24

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


(29) Park, J. U.; Hardy, M.; Kang, S. J.; Barton. K.; Adair, K.; Mukhopadhyay, D. K.; Lee, C. Y.; Strano, M. S.; Alleyne, A. G.; Georgiadis, J. G.; Ferreira, P. M.; Rogers, J. A. HighResolution Electrohydrodynamic Jet Printing. Nat. Mater. 2007, 6, 782-789. (30) Derby, B. Inkjet Printing of Functional and Structural Materials: Fluid Property Requirements, Feature Stability, and Resolution. Ann. Rev. Mater. Res. 2010, 40, 395-414 (31) Stringer, J.; Derby, B. Limits to feature size and resolution in ink jet printing. J. Eur. Ceram. Soc. 2009, 29, 913-918 (32) Tian, D.; Song, Y.; Jiang, L. Patterning of Controllable Surface Wettability for Printing Techniques. Chem. Soc. Rev. 2013, 42, 5184-5209 (33) Sirringhaus, H.; Kawase, T.; Friend, R. H.; Shimoda, T.; Inbasekaran, M.; Wu, W.; Woo, E. P. High-Resolution Inkjet Printing of All-Polymer Transistor Circuits. Science 2000, 290, 21232126 (34) Wang, J. Z.; Zheng, Z. H.; Li, H.; Huck, T. S.; Sirringhaus, H. Dewetting of conducting polymer inkjet droplets on patterned surfaces. Nat. Mater. 2004, 3, 171-176 (35) Svarnas, P.; Yang, L.; Munz, M.; Edwards, A. J.; Shard, A. G.; Bradly, J. W. Highly selective wettability on organic light-emitting-diodes patterns by sequential low power plasmas. J. Appl. Phys. 2010, 107, 103313 (36) Lee, A.; Jin, H.; Dang, H. W.; Choi, K. H.; Ahn, K. H. Optimization of Experimental Parameters to Determine the Jetting Regimes in Electrohydrodynamic Printing. Langmuir 2013, 29, 13630-13639. (37) Onses, M. S.; Sutanto, E.; Ferreira, P. M.; Alleyne, A. G.; Rogers, J. A. Mechanisms, Capabilities, and Applications of High-Resolution Electrohydrodynamic Jet Printing. Small 2015, 11, 4237-4266.


23


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

Page 24 of 24

“For Table of Contents Use Only”


24

Electrostatic-Force-Assisted Dispensing Printing of ... - ACS Publications

Recommend Documents