Single-layer organic light-emitting diode with 2.0% external quantum efficiency prepared by spin-coating

We present a highly efficient organic light-emitting diode with a single-layer structure and air-stable Al cathode. The device consists of a spin-coated thin film of polystyrene in which rubrene and Alq(3) molecules are dispersed. By optimizing the concentration of Alq(3) and rubrene, a maximum external quantum efficiency of 2.0% photons/electron and a current efficiency of 8.5 cd/A at 22 V could be achieved in the device. The high electroluminescence efficiency is attributed to a combination of energy transfer from Alq(3) to rubrene, and direct carrier trapping and recombination on rubrene, followed by an efficient fluorescent emission from rubrene. (C) 2000 Elsevier Science B.V. All rights reserved.