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 (C₆₀) as an interlayer between indium tin oxide (ITO) anode and hole transporting layer of N, N′-diphenyl-N, N′-bis(1,1′-biphenyl)-4,4′-diamine (NPB) and electron transporting layer (ETL) at the same time. The results are ascribed to the interfacial-dipole formation of C₆₀ on the surface of ITO anode and Ohmic cathode contact of C₆₀. The surface dipole of C₆₀ on the ITO anode helps to lower the hole injection energy barrier from ITO to NPB. C₆₀ also has an Ohmic cathode contact with high electron mobility in the typical structure of C₆₀/LiF/Al. These properties of C₆₀ 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 C₆₀ can eliminate Joule heating at both organic/cathode and organic/anode interfaces and as a result, provides the improved stability of OLEDs.

Keywords:

• buckminsterfullerene
• charge injection
• energy barrier for charge injection
• hole injection
• ohmic contact
• surface dipole