## 3 Results and Discussion  
To confirm the surface morphology of the Ag nanowire TEs before and after UAPR coating, SEM images were analyzed (Figure 2). The uncoated electrode exhibited a network structure (Figure 2a), while a smooth surface was observed for the UAPR-coated electrode (Figure 2b). Because the Ag nanowire TEs were uniformly covered by the UAPR, the network morphology was difficult to observe in the SEM image. To confirm the effect of the UAPR coating on the optical performance of the Ag nanowire TEs, their optical transmittance with and without UAPR was measured. The optical transmittance of an electrode is determined by its light reflection behavior, which needs to be closely controlled. In the UAPR-coated Ag nanowire electrodes, there were two major light reflection sources: the surface of the nanowires and the interface between the coating and the substrate. The use of long Ag nanowires with a small diameter increases the optical transmittance by reducing the fraction of the light reflected at the surface of the nanowires. However, there is a trade-off between the diameter and the length of the Ag nanowires; thus, controlling  
Figure 1: Illustration of the fabrication process for the UAPR-coated Ag nanowire transparent electrode: (**a**) coating of Ag nanowire on PET substrate, (**b**) UAPR coating with a doctor blade, (**c**) UV exposure to cure UAPR, (**d**) UAPR-coated Ag nanowire electrode. the dimensions of Ag nanowire TEs is challenging. Therefore, an alternative method to enhance the optical transmittance of Ag nanowire electrodes is required. Employing an appropriate coating material is a promising way to enhance the optical transmittance without controlling the Ag nanowire dimension. According to [PERSON]'s theory, the optical transmittance of Ag nanowire electrodes on a transparent substrate can be tuned using a coating layer. A coating material with a refractive index between that of the substrate and air reduces the amount of light reflected at the interface between the substrate and the coating, which can enhance the optical transmittance. UAPR, the coating material used in the present study, has a refractive index of \(\sim\)1.59, which is between that of polymer substrates that are widely used for Ag nanowire TEs, such as PET or polyethylene napthalate (PEN) and air. Therefore, employing UAPR is expected to enhance the optical transmittance of Ag nanowire TEs on a PET or PEN substrate. Table 1 presents the optical transmittance of Ag nanowire TEs fabricated on various substrates with and without the UAPR coating. Overall, the optical transmittance of the Ag nanowire electrodes was increased with the UAPR coating. The bare Ag nanowire electrodes on a PET substrate had an optical transmittance of \(\sim\)90.6%, which rose to \(\sim\)91.3% after coating. For the Ag nanowire electrodes on a PEN substrate, the optical transmittance before and after UAPR coating was \(\sim\)88.9% and \(\sim\)90.1%, respectively. The Ag nanowire electrodes on an ITO-covered PET substrate also exhibited greater optical transmittance. The increase in the optical transmittance with the use of UAPR coating is due to the refractive index of UAPR (\(\sim\)1.59), which is between that of the air (1.0) and the substrates (Table 1), as indicated by [PERSON]'s theory [29]. Therefore, it was confirmed that UAPR is an appropriate coating in terms of the enhancement of the optical transmittance. Protecting Ag nanowire TEs from the oxidation or sulfidation caused by the ambient air is also an important role of coating materials. To confirm that the UAPR coating could improve the ambient stability of Ag nanowire TEs, electrodes with and without the UAPR coating were exposed to ambient air for 180 h, and the change in optical transmittance and sheet resistance over time was measured. Figure 3a shows the variation in the optical transmittance of the Ag nanowire TEs with and without the UAPR coating as a function of exposure time to ambient air at 70 \({}^{\circ}\)C, which represents standard conditions for the