Efficient organic light‐emitting diodes using hole‐injection buffer layer

Abstract

We have investigated the effects of hole‐injection buffer layer in organic light‐emitting diodes using copper phthalocyanine (CuPc), poly(vinylcarbazole)(PVK), and Poly(3,4‐ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT: PSS) in a device structure of ITO/buffer/TPD/Alq3/Al. Polymer PVK and PEDOT:PSS buffer layer were produced using the spin casting method where as the CuPc layer was produced using thermal evaporation. Current‐voltage characteristics, luminance‐voltage characteristics and efficiency of device were measured at room temperature at various a thickness of the buffer layer. We observed an improvement in the external quantum efficiency by a factor of two, four, and two and half when the CuPc, PVK, and PEDOT:PSS buffer layer were used, respectively. The enhancement of the efficiency is assumed to be attributed to the improved balance of holes and elelctrons resulting from the use of hole‐injection buffer layer. The CuPc and PEDOT:PSS layer function as a hole‐injection supporter and the PVK layer as a hole‐blocking one.