Flexible, transparent patterned electrodes based on graphene oxide/silver nanowire nanocomposites fabricated utilizing an accelerated ultraviolet/ozone process to control silver nanowire degradation

www.nature.com/scientificreports OPEN Received: 4 June 2018 Accepted: 20 March 2019 Published: xx xx xxxx Flexible, transparent patterned electrodes based on graphene oxide/ silver nanowire nanocomposites fabricated utilizing an accelerated ultraviolet/ozone process to control silver nanowire degradation Dong Chul Choo1, Sang Kyung Bae2 & Tae Whan Kim1,2 We developed flexible, transparent patterned electrodes, which were fabricated utilizing accelerated ultraviolet/ozone (UV/O3)-treated graphene oxide (GO)/silver nanowire (Ag-NW) nanocomposites via a simple, low-cost pattern process to investigate the feasibility of promising applications in flexible/ wearable electronic and optoelectronic devices. The UV/O3 process of the GO/Ag-NW electrode was accelerated by the pre-heat treatment, and the degradation interruption of Ag NWs was removed by the GO treatment. After the deposition of the GO-treated Ag NW electrodes, the sheet resistance of the thermally annealed GO-treated Ag-NW electrodes was significantly increased by using the UV/O3 treatment, resulting in a deterioration of the GO-treated Ag NWs in areas exposed to the UV/O3 treatment. The degradation of the Ag NWs caused by the UV/O3 treatment was confirmed by using the sheet resistances, scanning electron microscopy images, X-ray photoelectron microscopy spectra, and transmittance spectra. While the sheet resistance of the low-density Ag-NW electrode was considerably increased due to the pre-thermal treatment at 90 °C for 10 min, that of the high-density Ag-NW electrode did not vary significantly even after a UV/O3 treatment for a long time. The degradation interference phenomenon caused by the UV/O3 treatment in the high-density Ag NWs could be removed by using a GO treatment, which resulted in the formation of a Ag-NW electrode pattern suitable for promising applications in flexible organic light-emitting devices. The GO treatment decreased the sheet resistance of the Ag-NW electrode and enabled the pattern to be formed by using the UV/O3 treatment. The selective degradation of Ag NWs due to UV/O3 treatment decreased the transparency of the Ag-NW electrode by about 8% and significantly increased its sheet resistance more than 100 times. Flexible electronic devices have been attractive because of interest in potential applications in next-generation intelligent systems1–3. Rapid advances in the development of silver-nanowire (Ag-NW) electrodes have made possible flexible, transparent electrodes4–6. Light-emitting devices fabricated utilizing flexible, transparent substrates have the possibility of being applied to various designs requiring strong impact resistance and high portability7–9. Among the various flexible, transparent electrodes, Ag-NW, graphene, and metal-mesh electrodes have emerged as excellent candidates for low-cost flexible, transparent electrodes9–13. Furthermore, the solution process used to fabricate the Ag-NW electrodes is simple and inexpensive to use, and the transmittances and the sheet resistances of the resulting Ag-NW electrodes are superior to those of other flexible electrodes. However, the commercialization of transparent Ag-NW electrodes has been hindered by their inherent problems: image blurring due to the haze phenomenon, very large surface roughness, and difficult pattern-formation process14–16. Due to improvements in the synthesis process, Ag NWs can be made thinner and longer, which would dramatically decrease the 1 Department of Electronics and Computer Engineering, Hanyang University, Seoul, 04763, Republic of Korea. Department of Information Display Engineering, Hanyang University, Seoul, 04763, Republic of Korea. Correspondence and requests for materials should be addressed to T.W.K. (email: ) 2 Scientific Reports | (2019) 9:5527 | https://doi.org/10.1038/s41598-019-41909-4 1 www.nature.com/scientificreports/ www.nature.com/scientificreports haze phenomenon associated with Ag-NW electrodes. Because the haze associated with Ag-NW electrodes can be reduced to less than 3% due to such improvements, the performances of those electrodes will not be significantly degraded compared with the performances of conventional transparent electrodes17. Moreover, the large surface roughness of Ag-NW electrodes can be reduced to a few nanometers by synthesizing ultra-thin Ag NWs, applying a planarization layer with a sufficient thickness, or transferring the Ag NWs to a polymer substrate18–20. A laser-patterning method has been extensively used to form Ag-NW patterns on electrodes21. Even though this method can form fine, high-quality Ag-NW patterns, because the process cost is very high, using this method to produce a large-sized product is difficult. Various patterning methods, such as the transfer of the Ag-NW patterns to a polymer substrate, photolithography, direct patterning, plasma etching, and magnetic printing, have been proposed as ways to overcome this inherent problem22–28. However, the methods used to form Ag-NW patterns involve complicated solutions and high-temperature processes, and they are still too complicated to be applied commercially to the fabrication of large-sized products. This paper reports a novel method for forming Ag-NW patterns on electrodes by using a thermal treatment, a graphene-oxide (GO) layer, and an ultraviolet/ozone (UV/O3) treatment. The GO-treated Ag-NW electrode was patterned by using a thermal annealing and a UV/O3 treatment through a mask in an atmospheric condition, which can be easily used in the production of large-area devices. Even though the thermal and UV/O3 treatments are relatively very simple processes, the combination of the two processes can effectively form a large-area Ag-NW electrode pattern. While the degradation of the GO-treated Ag-NW electrode due to the UV/O3 treatment was actually very slow, the pre-thermal treatment was able to decrease the degradation time effectively by changing the surface composition of the Ag-NWs. This pattern formation method can be combine with the various coating methods, resulting in a formation of more effective and lower cost process. While the conventional laser pattern method requires a high cost for enlarging the pattern area, it is possible to form a large area pattern at low cost by adding UV lamps necessary for the UV/O3 process used in this method. Furthermore, the patterning method proposed in this manuscript requires the same processing time even when the substrate area increases. The sheet resistances and the transmittance spectra were measured to investigate the electrical and the optical properties of the Ag-NW-patterned electrodes. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) measurements were performed to investigate the structural properties and the chemical compositions of those electrodes. Methods Sample preparation. Polyethylene terephthalate (PET) substrates were cleaned with methanol for 10 min, after which they were thoroughly rins (...truncated)