## 3 Result and Discussion
In the case of the PEDOT:PSS solution diluted with 90% EtOH, its viscosity value and surface tension value were measured to be about 1.3 cp and 22.8 mN/m, respectively. Therefore, we could predict and describe the behavior of pattern width variation would follow that seen in Figure 2a. Furthermore, we converted and calculated the relative film thickness without absolute scale of the PEDOT:PSS/EtOH pattern shape by using the grey scale method [14]. The grey scale method revealed that the coated pattern can absorb and reflect the light with various thicknesses of the layer, and therefore the pattern contrast of grey color intensity with pattern shape including width has a difference shadow. Thus, we could convert the thickness of the patterns, as shown in Figure 2b. The behavior of the pattern thickness by using the grey scale method was similar to the CCD camera images of the pattern shape. To fabricate a proper PEDOT:PSS line pattern, the remaining water concentration is also important. The evaporation rate change of the 90% EtOH volume concentration in PEDOT:PSS solution in a circular petri dish with an inner diameter of 35 mm and the evaporation rate was measured according to the EtOH volume concentration. The evaporation rate of 90% EtOH volume concentration in the PEDOT:PSS solution in the dish changed with time. Eventually, when the EtOH in the solution was completely dried, the evaporation rate was the same as the water evaporation rate. During the drying process, the measured evaporation rate could be used to calculate the volume concentration and EtOH in the remaining solution and the amount of remaining solution. As in the above result, we found that a uniform pattern, considering line width, depends on the remaining water concentration in the total solution. As a result, the optimized thickness uniformity was obtained at 90% EtOH volume concentration in PEDOT:PSS solution, and SEM was used to measure the actual thickness. To determine the  
Figure 2: (**a**) Charge-coupled device (CCD) camera images of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) pattern with containing various rate of EtOH solvent. (**b**) Shape of PEDOT:PSS patterns with various conditions by Simulating of Grey scale method. uniformity by grey intensity, the thickness profile of the width was measured at intervals of 100 \(\upmu\)m using SEM. Figure 3 shows the line width thickness profile measured by grey intensity and SEM. The thickness of both ends of the line was measured as about 160 nm due to the coffee ring effect and the thickness except for at both ends was measured to be about 18 nm. A thickness of about 18 nm was uniformly measured over about 3.5 mm scanning length. Also, we observed good film uniformity without any pinhole defects in Figure 3c. Finally, as seen from the results of the above PEDOT:PSS pattern behavior according to the dilution rate of EtOH, we fabricated the OLED device structure as glass/ITO/printed-PEDOT:PSS (\(w\)/EtOH 0%, 40%, 90%)/CBP:Ir(mppy)\({}_{3}\) (10% doped)/TPBi/LiF/Al. The whole group of OLED devices had a spectrum that arose in the electro luminance (EL), where a maximum peak of 515 nm was achieved. Additionally, EL spectrum yielded 1931 Commission Internationale de L'Eclairage (1931 CIE) chromaticity coordinates of (0.296, 0.623) approximately. According to the EL spectrum and CIE chromaticity coordinates, the nozzle-printed HIL based device emitted green light without any color shift. Figure 4 shows the I-V-L characteristics of the OLED devices. From the voltage-current density graph and voltage-luminance characteristics, device operated at almost 5 V (Figure 4a,b).