## 3 Results and Discussion  
Figure 2 shows the film morphology of the inkjet printing two types silver inks on a-IGZO/Al\({}_{2}\)O\({}_{3}\) at different substrate temperature (Supporting Information Figure S10). For silver nanoparticle ink, the evaporation rate of the droplets near the periphery area is larger than that at the center, accordingly creating a capillary flow from the center to the edge of the droplets, and carrying the suspended particles to the edge. As the substrate temperature increases, the effect was promoted and the film near the periphery area exhibited a shiny and silver appearance at 60 \({}^{\circ}\)C as shown in Figure 2a. For silver salt ink as shown in Figure 2b, the solutes migrated to the edge of the film at room temperature, thus the a-IGZO under layer at the central area is exposed. As the the substrate temperature increased, the solvent evaporation was accelerated, and the edges of the droplets were pinned on the substrate surface. At 40 \({}^{\circ}\)C, the film quality was improved, and uniform film was finally formed at 60 \({}^{\circ}\)C. To make the silver ink solvent vaporize quickly, the substrate temperature was defined at 60 \({}^{\circ}\)C.  
To further investigate the microscale differences of two kinds of printed silver electrodes, a SEM measurement was adopted. For silver nanoparticle ink, Figure 3a shows Ag particles randomly merged together after heat treatment, the overall density of the Ag electrodes is pretty good, but a number of boundaries exist between the silver particles. Comparatively, for silver salt ink, Figure 3b clearly shows that the electrode consisting of interconnected Ag particles and voids, which is demonstrated to be a typical phenomenon using silver salt ink. It is well known that the solvent evaporates quickly and the silver salt is reduced to silver nanoparticles during curing process, and eventually forms a conductive silver film with pores [25]. The XRD patterns in Figure 3c demonstrate that the two types  
Figure 2: Inkjet printed with (**a**) silver nanoparticles ink film and (**b**) silver salt ink film on a-IGZO/Al\({}_{2}\)O\({}_{3}\) with substrate temperatures of RT, 40 \({}^{\circ}\)C and 60 \({}^{\circ}\)C, respectively. of Ag electrodes have characteristic peaks of metallic pure silver with a good crystallization after thermal treatment. Figure 4a,b respectively show the output and transfer characteristics for the device by using silver nanoparticles ink (Supporting Information Figure S11). The device exhibits a poor electrical performance, which presents a mobility 0.15 cm\({}^{2}\)/V\(\cdot\)s, on/off current ratio of over 10\({}^{4}\), and turn-on voltage of about 6.1 V. Furthermore, the output curve shows unstable and low on current value, which decreases at high drain voltage bias and suggests the prevalence of charge traps. Comparatively, Figure 4c,d respectively show the output and transfer characteristics for the device by using silver salt ink. The device exhibits excellent field effect transistor characteristics, where the output curve shows a good saturation behavior. This device presents a higher mobility of 4.28 cm\({}^{2}\)/V\(\cdot\)s, a higher on/off current ratio of over 10\({}^{6}\), and a lower turn-on voltage close to zero. Figure 4: (**a**) Output and (**b**) transfer characteristics of the device with silver nanoparticle ink; (**c**) Output and (**d**) transfer characteristics of the device with silver salt ink. Figure 3: SEM images of the inkjet printed silver electrodes of TFTs by using (**a**) silver nanoparticles ink and (**b**) silver salt ink, respectively; (**c**) XRD patterns of the silver films after thermal treatment. TEM and EELS measurements were used to observe the Ag/a-IGZO interface and detect the distribution of elements of silver, carbon, and oxygen, and the result is shown in Figure 5. Figure 5a presents the TEM images of the Ag/a-IGZO structure fabricated using the silver salt ink, and the amplified area of the interface is shown in Figure 5b.