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-la yer structure and air-stable Al cathode. The device consists of a spin-coat ed thin film of polystyrene in which rubrene and Alq(3) molecules are dispe rsed. By optimizing the concentration of Alq(3) and rubrene, a maximum exte rnal quantum efficiency of 2.0% photons/electron and a current efficiency o f 8.5 cd/A at 22 V could be achieved in the device. The high electrolumines cence efficiency is attributed to a combination of energy transfer from Alq (3) to rubrene, and direct carrier trapping and recombination on rubrene, f ollowed by an efficient fluorescent emission from rubrene. (C) 2000 Elsevie r Science B.V. All rights reserved.