Improvement of efficiency in organic light-emitting diodes using PVK and CuPc buffer layer

Abstract

Abstract We have seen the effects of buffer layer in organic light-emitting diodes using poly(vinylcarbazole) (PVK) and copper phthalocyanine (CuPc) in a device structure of ITO/buffer/TPD/Alq3/Al. Polymer PVK buffer layer was made using spin casting method and CuPc layer was made using thermal evaporation. Current–voltage characteristics, luminance–voltage characteristics and external quantum efficiency were measured at room temperature with a thickness variation of PVK and CuPc layer. We have obtained an improvement of the external quantum efficiency by a factor of four when the PVK buffer layer is used. And we have also obtained an improvement of efficiency by a factor of two when the CuPc buffer layer is used. Our analysis shows that the PVK and CuPc layer are good candidates for hole-injection buffer layer. A reason for the improvement of the efficiency is that the PVK layer functions as a hole blocking and the CuPc layer as a hole injection supporter.