The Influence of Copper-phthalocyanine Layer, Heat Treatment, and Electric Field on the Performance of Poly (9-Vinylcarbazole)/Rhodamine B/Pb Organic Light Emitting Diodes

Abstract

In this work, two groups of samples have been prepared and their characterizations have been studied. The first group is a double layer device with the structure of ITO/PVK/Rhodamine B dye/Pb. Some of the samples were thermally annealed without any external electric field while others were treated by an external electric field during heating. The anealing process ocures after depositing the Rhodamine B dye layer on the PVK film, and before depositing Pb as a cathode. It is found that the annealing temperature of PVK/Rhodamine B layer increases the threshold voltage of the device except at 90°C. On the other hand, in the electric field-heat treatment, the threshold voltage is observed to decrease as the annealing temperature is increased and the maximum current density of the device is dramatically enhanced expect at 110°C. The second group is a multilayer device with the structure ITO/CuPc with different thicknesses/PVK/ Rhodamine B/Pb. The influence of copper-phthalocyanine (CuPc) hole-injection layer on the current voltage characteristic and the electroluminescence have been measured and studied. The results showed that the threshold voltage of the devices can be dramatically lowered by inserting the CuPc layer.