## 3 Result and Discussion  
In this study, we developed a nozzle printed PEDOT:PSS (as the HIL) wide line pattern for application to an OLED device. To this end, we attempted to determine the optimum PEDOT:PSS material as a HIL thin film with various concentrations of EtOH, a dilution solvent that is added to PEDOT:PSS, by using nozzle printer equipment. We described the behaviors through CCD camera images of the PEDOT:PSS pattern according to the dilution rate of EtOH, as presented in Figure 2a. The images were taken by a CCD camera after the samples were dried completely. As seen in Figure 2a, the narrowest line was formed in the sample with EtOH 0%. Furthermore, when the volume rate of EtOH was increased, the line width was greater than that of the pristine PEDOT:PSS based pattern. Also, we observed pattern contrast of grey color intensity with the pattern width as well as the behavior of the spreading, shrinking, and drying mechanism. As seen in these images, the pattern with 10% EtOH showed a bulging motion through the spreading and shrinking process and different surface tension between hetero-solvent systems. Also, from the point of line edge, we predicted that the shrinking mechanism occurred after the pinning effect. Through the samples with a ratio of EtOH from 20% to 40% showed an instable branched type pattern. Though the above group, the samples with EtOH of 20-40%, had a poor film shape, and the film uniformity of the PEDOT:PSS layer was enhanced with an increase of the volume rate of EtOH (50-90%). Finally, in the case of the 90% EtOH ratio in PEDOT:PSS, we obtained good spreading and a uniform film of PEDOT:PSS pattern. While the coffee ring effect still remains at the line edge, line width of almost 4 mm could cover a 2 mm \(\times\) 2 mm pixel area in the OLED device, and therefore entire film planarization was not necessary in this study. Also, as seen in the image of Figure 2a, the line width increased the EtOH ratio from 0% to 20%, and the line width reduced when the EtOH quantity ranged from 30% to 40%. Finally, in the case of the 50-90% range, the pattern width increased again. This indicated that when the EtOH volume concentration in the PEDOT:PSS solution was reduced from 90% to 50%, the printed line width was also reduced. However, when the EtOH volume concentration in the PEDOT:PSS solution was decreased from 40% to 0%, the viscosity decreased and the surface tension increased. When the EtOH volume concentration in the PEDOT:PSS solution was decreased from 40% to 20%, the decrease in viscosity was greater than the increase in surface tension, and hence the spreading proceeds faster and the line width was enhanced. However, when the EtOH volume concentration in the PEDOT:PSS solution was less than 20%, the value of the surface tension became larger, and therefore spreading was suppressed and the width was reduced. This phenomenon of variation was induced by the dynamic viscosity of the binary system [15]. Generally, PEDOT:PSS contains water. When a greater amount of ethanol is dissolved into water, ethanol molecules replaced water molecules between inter/intra-molecule of PEDOT:PSS with enhancement of the grain boundary of PEDOT:PSS [16,17]. When with the reason above, the viscosity of PEDOT:PSS would be increased relatively with an increase of EtOH, and concentration ratio of EtOH overcomes the threshold barrier of the covered-EtOH molecule at the surface of water, and thus the viscosity of the hetero-solution might be reduced. We also measured the viscosity and surface tension values of the hetero-solution. The viscosity of the PEDOT:PSS solution diluted with a 0% to 40% volume ratio of EtOH was shown to increase from about 10 cp to 25 cp. The viscosity of the PEDOT:PSS solution diluted with more than 40% was decreased from about 25 cpto 2.5 cp. The surface tension value of PEDOT:PSS solution (CH8000) was about 70 mN/m before being diluted with EtOH and its surface tension value was decreased to about 22.5 mN/m.