Material Science and Engineering

Biography

Biography: Apisit Chittawanij

Abstract

Organic light-emitting diodes (OLEDs) have been made for full color displays. However, many issues are involved in the fabrication of large-area OLED panels such as a short circuit, low luminous intensity, nonuniformity of light emission, etc.The nonuniform light distribution is attributed to the limiting conductivity of ITO. Therefore, an auxiliary metal electrode as grid patterned on ITO has been used. In this work, we investigate the feasibility to control the auxiliary metal electrodeeffects in OLEDs by introducing a striped Ag and Au metal layer between ITO/HTL layers. Toprovide guidelines for design optimization of large-area OLED panels such as the spaceand thickness of the patterned metal lines andthe OLED layer thickness are investigated. We have first fabricated the small-area (3x3 cm2) OLED device without auxiliary electrodeinstructureofITO/CuPc (10 nm)/NPB (40 nm)/Alq3(60 nm)/LiF (0.8 nm)/Al (150 nm).The resultshows the luminance, current efficiency and driving voltage of 764 cd/m2, 3.82 cd/A and 9.25 V, respectively, at 20 mA/cm2.Then, to obtainedhomogeneous light, we have deposited auxiliary Ag or Auon ITO, patterned Ag or Auin the form of a gridwith a grid space of 2, 4, and 6mmin device structureofITO/Agor Au(15 nm)/CuPc (10 nm)/NPB (40 nm)/Alq3(60 nm)/LiF (0.8 nm)/Al (150 nm). Itwas seen that the optimal auxiliary electrode material and line space ofAu in linespace 6 mm were obtained. The result shows the luminance, current efficiency and driving voltage of 690 cd/m2, 3.45 cd/A and 7.49 V, respectively, at 20 mA/cm2.The snapshot light emissionofthe 3x3 cm2OLED ofAu line space 6 mm metal gridswere investigated. The average luminance of420.9 cd/m2and uniform luminance of 95% at 10mA/cm2were achieved.This uniform luminance is higher than that of without metal grids about 9.8 %. Finally, the auxiliary electrode of Ag and Au grid wereapplied to the area of 6x6 cm2OLED device.The large-area OLED panel is shown in Fig. 1.The Au inline space 6 nm device shows highthe luminance, current efficiencyand low driving voltage is 203cd/m2, 2.03cd/A and 9.5Vat current density of 20 mA/cm2, respectively.While theAginline space 4nm device shows highuniform luminance of 94%. This indicates that the grid metal layers are expected to be helpful in reducing the sheet resistance of the transparent electrode;we expectedthat our approach can be easily integrated with existing OLED architectures, in particular, large-area device