# Effects of Intrinsic Factors on the Stability of Silver Nanowire-Based Flexible Electrodes
## 3 Results and Discussion
### Effects of Flexible Substrates on the Stability of AgNW Electrodes
Figure 3: The light stability of AgNW electrodes with 95 mg/m\({}^{2}\) of AgNW surface density at an ambient temperature of 25 \({}^{\circ}\)C. (**a**) PET–AgNW electrodes and (**b**) PVA–AgNW electrodes. Figure 2: The thermal stability of AgNW electrodes with 95 mg/m\({}^{2}\) of AgNW surface density. (**a**) PET–AgNW electrodes and (**b**) PVA–AgNW electrodes. Figure 4 shows a schematic diagram of the distribution of AgNPsWs on the electrode surface. For PET-AgNW electrodes, as shown in Figure 4a, silver nanowires are distributed evenly on the electrode surface, so all nanowires are exposed directly to the environment and are subjected to reaction with the atmosphere. For PVA-AgNW electrodes, as shown in Figure 4b, since silver nanowires are bound to PVA substrates by spin-coating PVA on the surface of silver nanowires, most of the silver nanowires would be encapsulated in the PVA film and a small portion of the silver nanowires are exposed on the surface. Therefore, compared to the PET-AgNW electrodes, the surfaces of the PVA-AgNW electrodes have much fewer silver nanowires in direct contact with ambient oxygen and moisture, and the surface reactive activity is lowered significantly. AFM images of the fresh surfaces of AgNW electrodes at room temperature of 25 \({}^{\circ}\)C are shown in Figure 5, which reflect the differences in the distributions of AgNPs on PET substrates and PVA substrates. The surface roughness of PVA-AgNWs is significantly reduced for a large number of AgNPs encapsulated by PVA compared to PET-AgNWs. However, it is important to note that the embedding of AgNPs in the PVA film may cause electrical shortcuts between the transparent electrode and the underlying layer, but this is unlikely to happen as long as the PVA film is thick enough to be greater than five times the diameter of the AgNPs (thicker than 150 nm). Although the resistance of PVA-AgNW electrodes is reduced by embedding in PVA films compared to PET-AgNW electrodes at the same surface density of AgNPs, our experimental results show that the resistance differences between PVA-AgNWs and PET-AgNWs are significantly reduced when the surface density of AgNPs is greater than 79 mg/mm\({}^{2}\) (as shown in Supplementary Materials). Therefore, when the surface area density of AgNPs is large enough, the encapsulation of AgNPs by PVA will not affect the electrical properties of PVA-AgNW electrodes. When the AgNW surface density was set to more than or less than 95 mg/m\({}^{2}\), it was found in our experiments that the thermal stability and the light stability of PVA-AgNW electrodes were still significantly better than those of PET-AgNW electrodes with the same AgNW surface density, as shown in Table 1.  
Figure 6 shows the SEM images of the surfaces of these two electrodes after 7 \(\times\) 24 h of illumination at high optical power density. Figure 6 reveals that many nanoparticles are generated on the surfaces of the PET-AgNW electrodes, whereas nanoparticles are fewer on the PVA-AgNW electrodes. Most of the nanoparticles on the AgNW surfaces are silver oxides [7; 8] and sulfides originating from the chemical reaction between AgNPs and the oxygen and moisture in the environment. It is also noticed from Figure 6a that, besides nanoparticles, there exist breakages of silver nanowires on the surfaces of PET-AgNW electrodes, which indicate that light exposure can not only cause chemical reactions on the surface of silver nanowires, but also cause physical damage to the silver nanowires and further accelerate the deterioration of the AgNW electrodes. According to the literature on the effect of light on the stability of AgNW electrodes [7; 8; 10], light irradiation on AgNW electrodes will cause a redox process, including oxidation of silver nanoparticles, migration of silver ions, and reduction of silver ions to new silver nanoparticles at other  
Figure 4: Schematic diagram of the distribution of AgNPs on electrode surfaces. (**a**) PET–AgNWs and (**b**) PVA–AgNWs.