# Effects of Intrinsic Factors on the Stability of Silver Nanowire-Based Flexible Electrodes
## 3 Results and Discussion
### Effects of the Surface Density of AgNWs on the Stability of AgNW Electrodes  
We prepared PVA-AgNW electrodes with silver nanowire surface densities of 64 mg/m\({}^{2}\) (S1), 95 mg/m\({}^{2}\) (S4), and 126 mg/m\({}^{2}\) (S5) and their thermal stabilities and light stabilities were tested and compared and are shown in Figure 7. It was found from Figure 7a that the resistance variations of the three types of electrodes have the same trend: resistance firstly decreases with time and after dropping down to a certain value the resistance starts to increase rapidly with time. This is in line with the behavior of the thermal stability of AgNW electrodes we observed above. It is noted that the resistance change rates differed greatly for the three types of electrodes. With the increase in surface density of silver nanowires, the change rate of electrode resistance decreases. The change rates of resistance for silver nanowire surface densities of 64 mg/m\({}^{2}\), 95 mg/m\({}^{2}\), and 126 mg/m\({}^{2}\) were 67.1%, 48.2%, and 45.1%, respectively. Figure 7b shows the resistance variations for three types of electrodes under high light power irradiation (optical power densities of 25.8 W/m\({}^{2}\) to 27.0 W/m\({}^{2}\) at 25 \({}^{\circ}\)C). It can be seen that the AgNW electrodes with different surface densities exhibit different light stabilities: after 7 \(\times\) 24 consecutive hours, the change rates of the square resistance for silver nanowire surface densities of 64 mg/m\({}^{2}\), 95 mg/m\({}^{2}\), and 126 mg/m\({}^{2}\) were 121.3%, 32.3%, and 16.2%, respectively, which indicates that the light stability of the electrodes improves with the increase in the silver nanowire surface density. Figure 6: The SEM images of the AgNW electrode surfaces after 7 \(\times\) 24 h of illumination at high optical power density. (**a**) PET–AgNW electrodes and (**b**) PVA–AgNW electrodes. Figure 7: The stability of PVA–AgNW electrodes with different AgNW surface densities. (**a**) Thermal stability at 80 \({}^{\circ}\)C and (**b**) light stability under high optical density illumination. A schematic diagram of the distributions of silver nanowires on electrode surfaces is shown in Figure 8a. Silver nanowires intersect with each other and form network junctions where they overlap, thus the discrete silver nanowires are linked together to form conductive pathways. The more such network junctions there are, the better the conductivity of the silver nanowires. Higher silver nanowire surface density, as well as large silver nanowire aspect ratios, are beneficial to increasing the number of junctions per unit area, but too high silver nanowire coverage will significantly affect the optical transmittance of the electrodes. Therefore, the silver nanowire surface density needs to be a balanced choice between electrode electrical conductivity and light transmittance. When a silver nanowire's surface density is small, most of the silver nanowires are distributed on the surface of the electrode, and the connected junctions are fewer and mostly distributed on the surface (as shown in Figure 8b). When subjected to external temperature or light, the surfaces of silver nanowires as well as the junctions undergo oxidation and fracture, and the electrical properties of the electrodes decline very rapidly because most of the silver nanowires and connecting junctions are exposed on the surface. As the surface density of silver nanowires increases, the number of silver nanowires distributed on the surface as well as the number of overlapping junctions increase, showing a multilayer structure (as shown in Figure 8c). Parts of the silver nanowires and connecting junctions are located inside the multilayer structure, so when the electrode is subjected to external light or temperature the silver nanowire network structure in the interior is less affected, thus reducing the degree of degradation in electrode performance.