High Luminance Organic Light-Emitting Diodes with Efficient Multi-Walled Carbon Nanotube Hole Injectors

2 ABSTRACT: We report high luminance organic light-emitting diodes with a simple and easy processing device structure, by use of acid functionalized multi-walled CNTs as efficient hole injectors. At only 10 V, the luminance can reach nearly 50,000 cd/m 2 with an external quantum efficiency over 2% and a current efficiency greater than 21 cd/A. The investigation of hole-only devices shows that the mechanism of hole injection is changed from injection limited to bulk limited because of the higher effective work function of the anode modified by o-MWCNTs. We expect the enhancement of the local electric field brought by dielectric inhomogeneities within o-MWCNTs, which improves hole injection from anode to organic active layer at much lower applied electric field. The results are among the best reported for undoped Tris(8-hydroxyquinolinato)aluminum (Alq 3) fluorescent devices, and the technology can be applied to other organic electronic devices that need high current density injection or extraction.