Significantly Improved Power Efficiency of Organic Light-Emitting Diodes with Surface Dipole on Anode and Ohmic Cathode Contact

Abstract

Dramatically improved power efficiency and stability of organic light-emitting diodes (OLEDs) were achieved by using buckminsterfullerene (C 60 ) as an interlayer between indium tin oxide (ITO) anode and hole transporting layer of N, N 0 -diphenyl-N, N 0 -bis(1,1 0 -biphenyl)-4,4 0 -diamine (NPB) and electron transporting layer (ETL) at the same time. The results are ascribed to the interfacial-dipole formation of C 60 on the surface of ITO anode and Ohmic cathode contact of C 60 . The surface dipole of C 60 on the ITO anode helps to lower the hole injection energy barrier from ITO to NPB. C 60 also has an Ohmic cathode contact with high electron mobility in the typical structure of C 60 =LiF=Al. These properties of C 60 make it possible to simultaneously enhance the electron and hole injection from both cathode and anode. Lowered operating voltage by surface dipole and Ohmic cathode contact of C 60 can eliminate Joule heating at both organic=cathode and organic=anode interfaces and as a result, provides the improved stability of OLEDs.