## 3 Results and Discussion  
The synthesized Ag NPs have an average diameter of 40 nm, and Ag NWs were 75 nm thick and less than 5 \(\upmu\)m long, as shown in Figure 1. Five composite inks were printed onto clean PI substrate by multiple passes (five passes). The composite electrodes printed with the five inks on the surface presented continuous, uniform and crack-free morphologies (see Figure 2a). When the ink was ejected from the nozzle, it spread out on substrate due to its low viscosity and high surface \begin{table}
\begin{tabular}{c c} \hline
**Filler** & **Dimension** \\ \hline AC(0D) & Amorphous form \\ AgNP(0D) & Average diameter: 40 nm, \\ CNT(1D) & Average diameter: 30 nm, Length: less than 2 \(\upmu\)m \\ AgNW(1D) & Average diameter: 75 nm, Length: less than 5 \(\upmu\)m \\ G(2D) & Average width: 10 \(\upmu\)m \\ \hline \end{tabular}
\end{table} 
Table 1: The dimensions of fillers. \begin{table}
\begin{tabular}{c c c c} \hline
**Sample** & **Filler** & **Solvent** & **Surfactant** \\  & **(30 wt.\%)** & **(69.9 wt.\%)** & **(0.1 wt.\%)** \\ \hline Pure Ag NP & Ag NP & H\({}_{2}\)O & EG & TX-100 \\ Ag NP/AC & 29.7\%Ag NP, 0.3\%AC & H\({}_{2}\)O & EG & TX-100 \\ Ag NP/Ag NW & 24\%Ag NP, 6\%Ag NW & H\({}_{2}\)O & EG & TX-100 \\ Ag NP/CNT & 29.7\%Ag NP, 0.3\%CNT & H\({}_{2}\)O & EG & TX-100 \\ Ag NP/G & 29.7\%Ag NP, 0.3\%G & H\({}_{2}\)O & EG & TX-100 \\ \hline \end{tabular}
\end{table} 
Table 2: Contents of composite inks. energy of PI (37 mN/m) [28], causing the line width of electrodes to be much larger than the original nozzle diameter (40 \(\upmu\)m), but could deposit evenly on the substrate. These binder-free inks allow thin electrode deposition. When printed five times, the thickness of electrodes was less than 2.4 \(\upmu\)m. Figure 2b shows the width and height of the as-printed composite electrodes. For example, Ag NP/AC electrode is 1.86 \(\upmu\)m thick, as shown in inset image of Figure 2b. Since no binders was used in these inks, the as-printed electrodes could dry at low temperature (50 \({}^{\circ}\)C). After drying, they showed very large resistance as thin PVP shells presented on the surface of Ag NPs, and the interfaces of Ag NPs or between Ag NPs with added the second phase of filler materials formed interconnections for electrons to pass through [29]. To increase its conductivity, laser sintering was used due to its high efficiency and selectivity in area [30]. In addition, it can significantly reduce the input heat and minimize thermal damage to PI substrates. Figure 3 shows a schematic of laser sintering process. When laser irradiates the nanoparticles, the effect of surface plasmonic triggers Ag NPs to convert light into heat [31]. This photothermal effect firstly resulted in the fracture of C-O-Ag bond between Ag NPs and PVP [32]. Consequently, it induced desorption or decomposition of the PVP layer of Ag NPs to leave a bare silver surface with high surface energy and high curvature for diffusion of surface atoms and nanoscopic interconnection [33]. In addition, plasmonic effect of silver caused by laser occurred at a small gap between two adjacent nanoparticles, making \"hot spots\" with high energy [34]. This concentration of light could induce a high temperature locally without heating the surroundings to minimize the heat damage to substrate as thermal sintering does [31; 35]. With the help of hot spots, local high temperature promoted the diffusion of atoms to form neck between Ag NPs during laser sintering [36]. Figure 1: The morphology of synthesized silver: (**a**) nanoparticles; and (**b**) nanowires. Figure 2: (**a**) Photograph and surface morphology of printed composite electrodes; and (**b**) thickness and line width of printed composite electrodes. Figure 4 shows the curve of resistivity as a function of the laser scanning times. The resistivity decreases significantly with the first few repeated scans and eventually remained stable with further increasing scanning times, indicating laser sintering induced many interconnections between conductive filler materials quickly.