High-Performance Transparent Quantum Dot Light-Emitting Diode

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Cite This: ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

High-Performance Transparent Quantum Dot Light-Emitting Diode with Patchable Transparent Electrodes Sunho Kim,†,# Jungwoo Kim,‡,# Daekyoung Kim,§ Bongsung Kim,∥ Heeyeop Chae,‡,§ Hyunjung Yi,*,† and Byungil Hwang*,⊥ †

Post-Silicon Semiconductor Institute, Korea Institute of Science and Technology, Seoul 02792, Republic of Korea School of Chemical Engineering and §Sungkyunkwan Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon 34141, Republic of Korea ∥ Nano-Convergence Mechanical Systems Research Division, Korea Institute of Machinery & Materials, Daejeon 34103, Republic of Korea ⊥ School of Integrative Engineering, Chung-Ang University, Seoul 06974, Republic of Korea

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S Supporting Information *

ABSTRACT: Patchable electrodes are attractive for applications in optoelectronic devices because of their easy and reliable processability. However, development of reliable patchable transparent electrodes (TEs) with high optoelectronic performance is challenging; till now, optoelectronic devices fabricated with patchable TEs have been exhibiting limited performance. In this study, Ag nanowire (AgNW)/ poly(methyl methacrylate) (PMMA) patchable TEs are developed and the highly efficient transparent quantum dot light-emitting diodes (QLEDs) using the patchable TEs are fabricated. AgNWs with optimized optoelectronic properties (figure of merit ≈ 3.3 × 10−2) are coated by an ultrathin PMMA nanolayer and transferred to thermal release tapes that enable physical attachment of TEs on the QLEDs without a significant damage to the adjacent active layer. The transparent QLEDs using patchable transparent top electrodes display excellent performance, with the maximum total luminance and current efficiency of 27 310 cd·m−2 and 45.99 cd·A−1, respectively. Fabricated by all-solution-based processes, these QLEDs exhibit the best performance to date among devices adopting patchable top electrodes. KEYWORDS: silver nanowire, patchable, transparent, thermal release tape, quantum dot light-emitting diode tronic properties and mechanical reliability.10−13 In addition, their capabilities for large-scale synthesis and facile coating of large substrates make them attractive from a manufacturing perspective.14 The use of nanoscale materials has become more prevalent as techniques for their transfer between different substrates have been developed.15−17 For example, the fabrication of graphene-based TEs in a roll-to-roll process became possible with the transfer technology of large-scale graphene on a Cu foil to a polymer substrate using a thermal release tape.18 In addition, the safe formation of a functional layer using nanoparticles (NPs) or quantum dots (QDs) without significant damage to the adjacent layer was enabled by transfer techniques suitably developed for each material.19 Ascoated AgNWs on a substrate generally exhibit high roughness, which degrades the stability of a device because of the abnormal concentration of current at a certain position.

1. INTRODUCTION Transparent electronics have attracted considerable attention for their potential application to various futuristic electronic devices, such as touchscreen panels, optoelectronic devices, smart windows, transparent sensors, transparent heaters, and supercapacitors.1−3 A challenging task in realizing flexible/ wearable electronic devices is the development of highly reliable and easily processable transparent electrodes (TEs), which serve as a key component in achieving optimal device performance under deformable conditions. Current electronic devices formed on rigid substrates mostly use indium tin oxide (ITO) as the TE, because ITO delivers excellent performance and high chemical stability.4 However, the formation of ITO TEs requires a plasma-based sputtering process with a postprocessing stage at high temperature, which causes severe damage to the adjacent active layers. Therefore, a number of alternatives to replace ITO, such as graphene, carbon nanotubes, conductive polymers, metal nanowires, nanofibers, and nanotroughs, have been intensively studied.5−9 Ag nanowires (AgNWs) are the most promising materials for flexible/stretchable devices owing to their excellent optoelec© XXXX American Chemical Society

Received: April 6, 2019 Accepted: June 20, 2019 Published: June 20, 2019 A

DOI: 10.1021/acsami.9b05969 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

ACS Applied Materials & Interfaces

QLEDs; hence, the fabricated QLEDs with the patchable TEs exhibited excellent light-emitting performance.

Transfer techniques have been used to solve this problem by embedding the AgNWs into soluble adhesives or polymer resins, which form TEs with reduced roughness after curing the resins.20 Optoelectronic devices, such as organic light-emitting diode (OLED) displays, QD light-emitting diode (QLED) displays, and organic solar cells (OSCs), require two electrodes: bottom- and top-side electrodes; one of these must be transparent to enable light to pass through the device. Although using TEs for both the top and bottom electrodes would allow the fabrication of advanced devices such as transparent or semitransparent displays, the current technology mostly employs a TE only for the bottom-side electrode because the formation of reliable TEs on the top-side is challenging. Thus far, several technologies have been reported for transparent or semitransparent devices with top-side TEs. For example, Kim et al. reported the fabrication of transparent OLEDs by depositing an ultrathin Ag layer on the top side via thermal evaporation.21 Although the ultrathin (less than ∼10 nm) Ag layer was transparent, showing 74% device transmittance, its deposition required a vacuum evaporation process, leading to concerns over high processing costs and thermal damage that may occur during deposition. Another approach by which top-side TEs have been formed involves the printing or coating of conductive inks with the appropriate printing or coating technologies, such as ink jet, doctor blade, spray system, or screen printing.22,23 Although those printing and coating technologies obviate the need for an expensive vacuum system, avoiding damage to the adjacent layer from the solvents in the inks remains a challenge. One approach to overcome the limitations of the current technologies in forming TEs on the top-side of a device might involve the patching of TEs with high optoelectronic properties on the device.10,24 In a patching system, the TE is fabricated on a patchable mediator, which is then transferred to the top-side of the device with a suitable transfer technology, such as lamination or hot pressing. The patching system is beneficial for application to electronic devices because forming the TEs on the devices is easy, does not involve an expensive vacuum process, and avoids solvent damage to the adjacent layer. Utilizing the benefits of a patchable system, several transparent QLEDs, OSCs, and polymer LEDs have been demonstrated using graphene- or conducting polymer-based patchable TEs;25−27 however, the devices’ performance remained unsatisfactory. Although AgNW-based TEs display superior optoelectronic properties compared with graphene- or conducting polymer-based TEs,28 which can result in high device performance, reports on the fabrication of AgNW-based patchable TEs and successful demonstrations of transparent optoelectronic devices using those TEs are limited. In this study, we developed AgNW-based patchable TEs using poly(methyl methacrylate) (PMMA) films as a mediator and demonstrated the successful operation of transparent QLEDs. For this, a two-step transfer technology was proposed, in which, first, AgNWs on a hydrophobic substrate were transferred to a PMMA nanolayer; then, the AgNW/PMMA were transferred to a thermal release tape. The fabricated AgNW/PMMA patchable TEs were highly conductive and transparent, and they could be attached to the fully solutionprocessed QLEDs device via simple hot pressing. This resulted in no significant damage to the adjacent active layers in the

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2. EXPERIMENTAL SECTION

2.1. Materials. AgNW solution (average diameter and length: ∼25 nm and ∼25 μm, respectively; solid content: 0.5 wt %, dispersed in isopropyl alcohol; N&B Co., Ltd.), PMMA powder (Mw 996 000, Sigma-Aldrich), thermal release tape (Tapeworld), and perfluorodecyltrichlorosilane (FDTS, Sigma-Aldrich) were used. PMMA solution (4 wt %) was prepared by dissolving PMMA powder in anisole (Daejung). 2.2. AgNW/PMMA Patchable TE Fabrication. A substrate (e.g., glass or silicon wafer) was hydrophobized by treatment with FDTS to facilitate the complete transfer of the AgNWs from the substrate to the thermal release tape. The AgNW solution was spin-cast on the FDTS-treated substrates at 1000 rpm for 30 s. For patterning, the AgNWs coated on the FDTS-treated substrates were covered with a shadow mask, shown in Figure S1, and were then placed in an O2 plasma-generation chamber (Femto Science) at 50 W for 180 s. The area of the AgNWs selectively exposed through the mask was oxidized during the O2 plasma treatment, and it was then removed by washing with NH3 solution (30 wt %), thereby forming the patterned AgNWs.29 For further details, see ref 29. On the AgNWs, PMMA solution was spin-cast at 1000 rpm for 20 s and they were dried at room temperature. To fabricate the patchable TEs, thermal release tape was attached manually on the AgNW/PMMA using a roller in a moderate press. By immersing the samples in a water bath, the FDTStreated substrates were easily removed, and the remaining AgNW/ PMMA/thermal release tape was removed from the bath and dried with an air blower. 2.3. Inverted Quantum Dot Light-Emitting Diodes. Commercially available patterned ITO (150 nm)-coated glass substrates as the bottom electrodes and connecting electrodes (AMG Glass) were prepared (Figure S2). The patterned ITO glass was cleaned by ultrasonication using acetone and methyl alcohol for 15 min at room temperature, and it was moved to a N2-filled glovebox. Then, ZnO nanoparticle (NP) layers (120 nm) were deposited by spin-coating onto the ITO substrate at 1500 rpm for 30 s and baked at 180 °C for 30 min. For the QD emissive layer (30 nm), the CdSe@ZnS/ZnS QDs (PL quantum yield 82.2%, emission wavelength 530.1 nm) (Figures S3 and S4) in a mixed solvent of octane/hexane (25 mg· mL−1) were spin-coated at 3000 rpm for 30 s on the ZnO-coated samples and they were then baked at 120 °C for 10 min. The ZnO NPs and CdSe@ZnS/ZnS QDs were prepared by the procedures described in the Supporting Information. Polyethylenimine ethoxylated (PEIE) (1 wt % in 2-methoxyethanol, Sigma-Aldrich), poly(N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine) (polyTPD) (10 mg·mL−1 in chlorobenzene, Solaris Chem, Inc.) (30 nm), and phosphomolybdic acid hydrate ((MoO3)12·H3PO4·(H2O)x, PMAH, 10 mg·mL−1 in acetonitrile, Sigma-Aldrich) (15 nm) layers were sequentially spin-deposited at 3000 rpm for 30 s, followed by annealing at 150 °C for 10 min, 150 °C for 20 min, and 150 °C for 10 min, respectively. Finally, the patchable electrodes (730 nm) were attached on the top side by a hot-pressing method at 100 °C and 2.5 MPa for 30 s. QLED performance was measured using a spectroradiometer (CS-2000, Konica Minolta Sensing, Inc.) and a source meter (Keithley 2400, Keithley Instruments, Inc.). The active area of the QLED devices for device performance characterization was 9 mm2. 2.4. Characterization. A noncontact resistance probe (Napson EC-80P) and UV−vis spectroscopy (Cary 5000) were used to measure sheet resistance and transmittance, respectively. Scanning electron microscopy (SEM) images were obtained using NOVA 200 Nanolab (FEI). Atomic force microscope topography (AFM, XE-100) was used to investigate the surface flatness of the AgNWs. The thickness of the PMMA layer was characterized with an α-Step profiler (KLA-Tencor). B

DOI: 10.1021/acsami.9b05969 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

ACS Applied Materials & Interfaces

3. RESULTS AND DISCUSSION Figure 1 shows the fabrication process for the AgNW patchable TEs. The process involves two transfer steps, in which, first, the

Figure 2. (a) UV−vis transmittance spectra of the AgNW/PMMA as a function of the number of AgNW coatings (1−4 times). (b) Transmittance at 550 nm of (a) versus the sheet resistance measured for each sample with the different number of AgNW coatings. Figures of merit were calculated from the transmittance and sheet resistance values and are presented together in (b). The numbers in parenthesis denote the number of AgNW coatings.

shows the transmittance spectra and optoelectronic properties of the AgNW/PMMA TEs as a function of the number of coatings, along with the transmittance of the bare PMMA for reference. As the number of coating cycles increased, both the transmittance and sheet resistance of the AgNW TEs decreased because of the increased density of the AgNWs owing to the multiple coatings, as expected. However, in terms of the FOM, the AgNWs coated twice showed the highest value of ∼3.3 × 10−2, as shown in Figure 2b. Thus, all devices demonstrated in this study used twice-coated AgNW samples. The AgNWs without PMMA showed similar FOM values and a similar trend for the change in FOM as a function of repeated coating, as shown in Figure S7. The key material in the fabrication process of the transparent QLEDs with our AgNW/PMMA patchable electrodes was the thermal release tape. Under hot pressing, the thermal release tape was easily removable because its adhesiveness was eliminated by the applied thermal energy; only the AgNW/PMMA TE was transferred and physically attached on the QLEDs to function as the top electrode (Figure 1b). The dry transfer processes, including tape attachment/removal and hot pressing, resulted in no significant change in either the sheet resistance or transmittance during the processes, which revealed that our transfer process was highly efficient without a significant loss of optoelectronic properties, as shown in Figure 3a−f. In addition to the use of the thermal release tapes, several other techniques were examined in this study to facilitate the facile fabrication of QLEDs with high optoelectronic performance. For example, the top electrodes must be patterned in optoelectronic devices to prevent shorting problems with the bottom electrodes. For the facile fabrication of patterned top electrodes, an O2 plasma treatment method was used, followed by NH3 washing. By covering the AgNW TEs with a shadow mask, the AgNWs selectively exposed to O2 plasma were oxidized and transformed from Ag to Ag2O, which was easily removed by NH3 washing (Figure S1). This technique allowed the fabrication of patterned AgNW TEs without a complicated photolithography process. The structure of the QLED employing the AgNW/PMMA patchable TE as the top electrode is illustrated in Figure 4a. A cross-sectional TEM image was also recorded for the QLED, as shown in Figure 4b. The green inverted structure of the QLED device was used for demonstration, and the sequential stack of the device layers was ITO/ZnO/QD/polyethylenimine ethoxylated (PEIE)/poly(N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)-

Figure 1. Schematic illustrations of (a) the AgNW/PMMA TE fabrication process and (b) the applications to transparent QLEDs.

AgNWs are transferred into PMMA, and then, the PMMAcoated AgNWs are transferred to a thermal release tape. Keys to success in the first transfer step are as follows: (1) treatment of the substrates with FDTS to increase their surface hydrophobicity and (2) the ultrathin PMMA coating to mediate AgNW transfer. The hydrophobicity of the substrate surface allowed the successful transfer of the AgNW/PMMA to the thermal release tape. In addition, the ultrathin PMMA film with a thickness of ∼730 nm (Figure S5) was easily processable, requiring no UV or heat treatment for curing. It was highly transparent, with ∼100% transmittance, which resulted in the excellent optoelectronic properties of the fabricated AgNW patchable TE. In detail, AgNWs were spincast on the hydrophobic substrate, which was then covered by spin-casting an ultrathin PMMA film. As the PMMA dried in air at room temperature, the AgNWs were embedded into the PMMA film (Figure S6) and the the AgNWs were successfully transferred from the hydrophobic substrate to the PMMA film. In the second transfer step, a thermal release tape was attached on the PMMA-covered AgNW TE, after which the hydrophobic substrate was removed. Maximizing the value of the figure of merit (FOM), defined as a quantitative measure of the optoelectronic properties of the TE, is important to achieve high performance of the optoelectronic device using the TE. For the AgNW TEs, the FOM is calculated according to ϕTE = T10·Rs−1,30 where T is the transmittance and Rs is the sheet resistance, which varies mostly depending on the AgNW density. Thus, determining the optimal AgNW density to achieve a maximum FOM is important for fabricating TEs with high optoelectronic performance. To optimize the AgNW density, the number of times they were coated on the hydrophobic glass substrates was varied and the optical transmittance and sheet resistance of each specimen were measured after the PMMA coating to evaluate the FOM as a function of AgNW density. Figure 2a,b C

DOI: 10.1021/acsami.9b05969 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces

Figure 3. Photos of (a) as-coated AgNW/PMMA on a glass substrate (4 cm × 4 cm) and the bare thermal release tape; (b) transferred AgNW/ PMMA on the thermal release tape, and the remaining glass substrate without the AgNWs; and (c) AgNW/PMMA transferred to the glass substrate by hot pressing and the released thermal release tape. Ag paste was used to connect the AgNWs to the alligator electrodes. (d) Photo of LED operation with the transferred patchable TE. (e) Sheet resistance and (f) UV−vis transmittance spectra measured for the as-coated AgNW/ PMMA samples in (a) and the transferred AgNW in (c) after all transfer processes were complete.

Figure 4. (a) Schematic structure and (b) cross-sectional TEM image of an inverted transparent QLED with a patchable AgNW/PMMA top electrode. (c) Photos of the QLEDs before and after the turn-on voltage. (d) UV−vis transmittance spectra of the top (AgNW/PMMA) and bottom (ITO glass) electrodes and the QLEDs with and without the AgNW/PMMA top electrodes.

benzidine) (poly-TPD)/MoOx/AgNW/PMMA. All fabrication steps, except ITO deposition, involved solution-based processes. More importantly, the device was transparent, as shown in the photograph in Figure 4c (left), and the light emitted by the QDs emerged through both the top and bottom sides (Figure 4c (right)). To evaluate the transparency of the fabricated QLEDs, the transmittance was measured for the key components, including the freestanding top electrodes using AgNW/PMMA TEs, the bottom electrodes using ITO (150 nm)-covered glass substrates, the partial stack of QLEDs without the AgNW/PMMA TE, and the full stack of QLEDs with the AgNW/PMMA TEs. The overall transmittance for the bottom and top electrodes was similar, with values of 89.4

and 86.8% at a wavelength of 550 nm (Figure 4d), respectively; thus, the efficiency of light emission through both sides was also expected to be nearly the same. The partially stacked QLEDs without the AgNW/PMMA TEs were still highly transparent, with a transmittance of 78.1%. Although the transmittance of the fully stacked QLEDs with the AgNW/PMMA TEs decreased to 70.1%, this value still satisfied the standard for a high-performance transparent display, i.e., T > 70%. The transparency of the QLEDs can be further improved by optimizing the optoelectronic properties of AgNW TEs by using thinner and longer AgNWs, as well as by adopting an appropriate overcoating layer that will reduce the reflection of light scattering. Finding appropriate overD

DOI: 10.1021/acsami.9b05969 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

ACS Applied Materials & Interfaces

Figure 5. Performance of the transparent QLEDs with the AgNW/PMMA top electrodes: (a) Current density−voltage, (b) luminance−voltage, and (c) current efficiency characteristics.

maximum FOM value, were transferred to an ultrathin PMMA nanolayer in the first step and then were transferred to a thermal release tape that enabled the successful transfer of the AgNW/PMMA patchable TEs to the top layer of the QLEDs without significant damage to the adjacent active layer. The maximum total luminance and current efficiency values for the fabricated QLEDs were 27,310 cd·m−2 and 45.99 cd·A−1 (bottom: 12,408 cd·m−2 at 12 V and 27.82 cd·A−1 at 7 V, top: 14,902 cd·m−2 at 10.5 V and 18.17 cd·A−1 at 8.5 V), respectively. These values are the best to date among those obtained using devices adopting patchable top electrodes. Our material and fabrication system will help to solve the challenging issue in the QLED industry of reducing the complexity of device fabrication while increasing the efficiency of the devices.

coating materials that can improve the transparency of the QLEDs and investigating the detailed mechanism of transparency improvement will be topics considered in our future research. The device performance of the fully stacked transparent QLEDs was characterized in terms of current density− voltage−luminance (J−V−L) characteristics and current efficiency, as shown in Figure 5a−c. The current density, luminance, and current efficiency measured at the top and bottom sides in the region over the turn-on voltage (>5.5 V) exhibited similar trends, as expected from the similar transmittance values of the top and bottom electrodes. Furthermore, the fabricated QLEDs demonstrated excellent performance, showing maximum total luminance and current efficiency values of 27 310 cd·m−2 and 45.99 cd·A−1 (bottom: 12 408 cd·m−2 at 12 V and 27.82 cd·A−1 at 7 V, top: 14 902 cd· m−2 at 10.5 V and 18.17 cd·A−1 at 8.5 V), respectively. To the best of our knowledge, this performance sets a new record among devices adopting patchable electrodes (Table S1). Moreover, compared with the QLEDs with the Al electrodes, the operating lifetime of the QLEDs with AgNW TEs was fairly long under continuous direct current (DC) operating conditions without encapsulation (Figure S8). Because light reflection by Al electrodes enhances luminance, the QLEDs with AgNW TEs showed relatively lower luminance. In addition, because the QLED lifetime test was carried out without encapsulation, the characteristics of the devices were degraded in a short time. It is generally accepted that a suitable protective layer should be required for commercialization of QLEDs because the materials of QLEDs, especially QDs, are unstable and sensitive to air and/or moisture. Additional studies on process and device optimization can help achieve a longer lifetime. The thickness of the PMMA layer in the submicron range had no significant effect on the transmittance value of the TEs that resulted in the similar QLED lightemitting performances, as shown in Figure S9. The excellent light-emitting performances confirmed that this material and fabrication system combination of AgNW/PMMA patchable TEs and the developed safe transfer method of the TEs to the QLEDs without loss of conductivity as well as no significant damage to adjacent active layers will be remarkably promising for the fabrication of highly efficient transparent QLEDs.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.9b05969. Synthesis of ZnO NPs and QDs; patterning of AgNWs; illustration of the patterned ITO; TEM images of QDs and ZnO NPs; absorption spectra of ZnO NPs and PL spectra of QDs; thickness of PMMA-covered AgNWs; SEM and AFM images of AgNWs embedded in PMMA; comparison of the optoelectronic performance between AgNWs and PMMA-covered AgNWs; DC operating lifetime comparison between the QLED with AgNW and Al; current density−voltage plot of the transparent QLEDs with different thicknesses of PMMA; comparison of the performances of LED devices with patchable electrodes (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (H.Y.). *E-mail: [email protected] (B.H.). ORCID

Heeyeop Chae: 0000-0002-6380-0414 Hyunjung Yi: 0000-0001-8812-497X Byungil Hwang: 0000-0001-9270-9014

4. CONCLUSIONS In this study, we developed AgNW/PMMA patchable TEs with excellent optoelectronic properties and demonstrated the realization of highly efficient transparent QLEDs. A two-step transfer method was developed to fabricate the AgNW/PMMA patchable TEs, in which the AgNWs, optimized for the

Author Contributions #

S.K. and J.K. contributed equally to this work.

Notes

The authors declare no competing financial interest. E

DOI: 10.1021/acsami.9b05969 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

ACS Applied Materials & Interfaces

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Silver Nanostructure Electrodes for Flexible Printed Energy Storage System. Mater. Des. 2018, 151, 1−7. (18) Bae, S.; Kim, H.; Lee, Y.; Xu, X.; Park, J.-S.; Zheng, Y.; Balakrishnan, J.; Lei, T.; Kim, H. R.; Song, Y. I.; et al. Roll-to-Roll Production of 30-Inch Graphene Films for Transparent Electrodes. Nat. Nanotechnol. 2010, 5, 574. (19) Keum, H.; Jiang, Y.; Park, J. K.; Flanagan, J. C.; Shim, M.; Kim, S. Photoresist Contact Patterning of Quantum Dot Films. ACS Nano 2018, 12, 10024−10031. (20) Ok, K.-H.; Kim, J.; Park, S.-R.; Kim, Y.; Lee, C.-J.; Hong, S.-J.; Kwak, M.-G.; Kim, N.; Han, C. J.; Kim, J.-W. Ultra-Thin and Smooth Transparent Electrode for Flexible and Leakage-Free Organic LightEmitting Diodes. Sci. Rep. 2015, 5, No. 9464. (21) Kim, D. Y.; Han, Y. C.; Kim, H. C.; Jeong, E. G.; Choi, K. C. Highly Transparent and Flexible Organic Light-Emitting Diodes with Structure Optimized for Anode/Cathode Multilayer Electrodes. Adv. Funct. Mater. 2015, 25, 7145−7153. (22) Han, K.; Xie, M.; Zhang, L.; Yan, L.; Wei, J.; Ji, G.; Luo, Q.; Lin, J.; Hao, Y.; Ma, C.-Q. Fully Solution Processed Semi-Transparent Perovskite Solar Cells with Spray-Coated Silver Nanowires/Zno Composite Top Electrode. Sol. Energy Mater. Sol. Cells 2018, 185, 399−405. (23) Zimmermann, J.; Porcarelli, L.; Rödlmeier, T.; SanchezSanchez, A.; Mecerreyes, D.; Hernandez-Sosa, G. Fully Printed Light-Emitting Electrochemical Cells Utilizing Biocompatible Materials. Adv. Funct. Mater. 2018, 28, No. 1705795. (24) Shin, D. H.; Jang, C. W.; Lee, H. S.; Seo, S. W.; Choi, S.-H. Semitransparent Flexible Organic Solar Cells Employing DopedGraphene Layers as Anode and Cathode Electrodes. ACS Appl. Mater. Interfaces 2018, 10, 3596−3601. (25) Seo, J.-T.; Han, J.; Lim, T.; Lee, K.-H.; Hwang, J.; Yang, H.; Ju, S. Fully Transparent Quantum Dot Light-Emitting Diode Integrated with Graphene Anode and Cathode. ACS Nano 2014, 8, 12476− 12482. (26) Yao, L.; Fang, X.; Gu, W.; Zhai, W.; Wan, Y.; Xie, X.; Xu, W.; Pi, X.; Ran, G.; Qin, G. Fully Transparent Quantum Dot LightEmitting Diode with a Laminated Top Graphene Anode. ACS Appl. Mater. Interfaces 2017, 9, 24005−24010. (27) Kee, S.; Kim, N.; Park, B.; Kim, B. S.; Hong, S.; Lee, J. H.; Jeong, S.; Kim, A.; Jang, S. Y.; Lee, K. Highly Deformable and Seethrough Polymer Light-Emitting Diodes with All-ConductingPolymer Electrodes. Adv. Mater. 2018, 30, No. 1703437. (28) HwanáKo, S. A Dual-Scale Metal Nanowire Network Transparent Conductor for Highly Efficient and Flexible Organic Light Emitting Diodes. Nanoscale 2017, 9, 1978−1985. (29) Kim, H.; Lee, G.; Becker, S.; Kim, J.-S.; Kim, H.; Hwang, B. Novel Patterning of Flexible and Transparent Ag Nanowire Electrodes Using Oxygen Plasma Treatment. J. Mater. Chem. C 2018, 6, 9394−9398. (30) Haacke, G. New Figure of Merit for Transparent Conductors. J. Appl. Phys. 1976, 47, 4086−4089.

ACKNOWLEDGMENTS This work was supported by the National Research Foundation (NRF) of Korea, which is funded by the Ministry of Science, Information and Communications Technology (Grant nos. NRF-2018R1C1B5043900 and 2019K1A3A1A25000230).

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REFERENCES

(1) Hwang, B.; Yun, T. G. Stretchable and Patchable Composite Electrode with Trimethylolpropane Formal Acrylate-based Polymer. Comp. Part B: Eng. 2019, 163, 185−192. (2) Lund, A.; van der Velden, N. M.; Persson, N.-K.; Hamedi, M. M.; Müller, C. Electrically Conducting Fibres for E-Textiles: An Open Playground for Conjugated Polymers and Carbon Nanomaterials. Mater. Sci. Eng., R 2018, 126, 1−29. (3) Kim, D.; Fu, Y.; Kim, S.; Lee, W.; Lee, K.-H.; Chung, H. K.; Lee, H.-J.; Yang, H.; Chae, H. Polyethylenimine Ethoxylated-Mediated AllSolution-Processed High-Performance Flexible Inverted Quantum Dot-Light-Emitting Device. ACS Nano 2017, 11, 1982−1990. (4) Choi, M. K.; Yang, J.; Kim, D. C.; Dai, Z.; Kim, J.; Seung, H.; Kale, V. S.; Sung, S. J.; Park, C. R.; Lu, N.; et al. Extremely Vivid, Highly Transparent, and Ultrathin Quantum Dot Light-Emitting Diodes. Adv. Mater. 2018, 30, No. 1703279. (5) Lee, K. Y.; Byeon, H. H.; Jang, C.; Choi, J. H.; Choi, I. S.; Jung, Y.; Kim, W.; Chang, J.; Yi, H. Hydrodynamic Assembly of Conductive Nanomesh of Single-Walled Carbon Nanotubes Using Biological Glue. Adv. Mater. 2015, 27, 922−928. (6) Wu, H.; Kong, D.; Ruan, Z.; Hsu, P.-C.; Wang, S.; Yu, Z.; Carney, T. J.; Hu, L.; Fan, S.; Cui, Y. A Transparent Electrode Based on a Metal Nanotrough Network. Nat. Nanotechnol. 2013, 8, 421. (7) Secor, E. B.; Lim, S.; Zhang, H.; Frisbie, C. D.; Francis, L. F.; Hersam, M. C. Gravure Printing of Graphene for Large-Area Flexible Electronics. Adv. Mater. 2014, 26, 4533−4538. (8) Kim, S.; Hwang, B. Ag Nanowire Electrode with Patterned Dry Film Photoresist Insulator for Flexible Organic Light-Emitting Diode with Various Designs. Mater. Des. 2018, 160, 572−577. (9) Lian, L.; Dong, D.; Wang, H.; He, G. Highly Reliable Copper Nanowire Electrode with Enhanced Transmittance and Robustness for Organic Light Emitting Diodes. Org. Electron. 2019, 65, 70−76. (10) Liang, J.; Li, L.; Niu, X.; Yu, Z.; Pei, Q. Elastomeric Polymer Light-Emitting Devices and Displays. Nat. Photonics 2013, 7, 817. (11) Liang, J.; Li, L.; Tong, K.; Ren, Z.; Hu, W.; Niu, X.; Chen, Y.; Pei, Q. Silver Nanowire Percolation Network Soldered with Graphene Oxide at Room Temperature and Its Application for Fully Stretchable Polymer Light-Emitting Diodes. ACS Nano 2014, 8, 1590−1600. (12) Lee, C.; Kim, H.; Hwang, B. Fracture Behavior of Metal Oxide/ Silver Nanowire Composite Electrodes under Cyclic Bending. J. Alloys Compd. 2019, 773, 361−366. (13) Lee, Y.; Suh, M.; Kim, K.; Kim, H.; Kim, D.; Chang, H.; Lee, D.; Kim, Y.; Kim, S. W.; Jeon, D. Y. Conjugated PolyelectrolyteAssisted Vacuum-Free Transfer-Printing of Silver Nanowire Network for Top Electrode of Polymer Light-Emitting Diodes. Org. Electron. 2017, 43, 64−69. (14) An, C.-H.; Kim, S.; Lee, H.-J.; Hwang, B. Facile Patterning Using Dry Film Photo-Resists for Flexible Electronics: Ag Nanowire Networks and Carbon Nanotube Networks. J. Mater. Chem. C 2017, 5, 4804−4809. (15) Li, H.; Wu, J.; Huang, X.; Yin, Z.; Liu, J.; Zhang, H. A Universal, Rapid Method for Clean Transfer of Nanostructures onto Various Substrates. ACS Nano 2014, 8, 6563−6570. (16) Lee, S.-W.; Kang, T.-H.; Lee, S. K.; Lee, K.-Y.; Yi, H. Hydrodynamic Layer-by-Layer Assembly of Transferable Enzymatic Conductive Nanonetworks for Enzyme-Sticker-Based Contact Printing of Electrochemical Biosensors. ACS Appl. Mater. Interfaces 2018, 10, 36267−36274. (17) Kim, S.; Yun, T. G.; Kang, C.; Son, M.-J.; Kang, J.-G.; Kim, I.H.; Lee, H.; An, C.-H.; Hwang, B. Facile Fabrication of Paper-based F

DOI: 10.1021/acsami.9b05969 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX