Electrical Conductive Mechanism of Organic Light-Emitting Diodes Depending on the Surface Roughness of Alq(3) Layer

Abstract

In a single-layered structure of ITO/Alq(3)/Al device, electrical conductive mechanism of organic light-emitting diodes were studied depending on the surface roughness of tris(8-hydroxyquinoline) aluminum (Alq(3)) layer. Several different sizes of holes on boat and several different deposition rates were employed in evaporating the organic materials. It was found that the hole size of the crucible boat and the evaporation rate affects the surface roughness of Alq(3) layer as well as the performance of the device. When the hole size of crucible boat and the deposition rate of Alq(3) are 1.0mm and 2.5 angstrom/s, respectively, an average surface roughness of the Alq(3) layer is lower and the efficiency of the device is higher than the ones made with other conditions. From the analysis of current density-luminance-voltage characteristics of the device, it was able to identify four conductive mechanisms depending on the voltage region. It was found that a coefficient beta(ST) in Schottky region is 3.28 x 10(-24), a coefficient beta(PF) in Poole-Frenkel region is 6.33 x 10(-24), and a potential barrier phi(FN) in Fowler-Nordheim region is 0.32 eV.