Amorphous carbon nitride thin films as buffer layer in organic LEDs

Abstract

Amorphous carbon nitride thin films (a-C:N) deposited by diode rf sputtering were used as buffer layers in organic light emitting diodes. The devices consist of the heterojunction structure: indium tin oxide (ITO)/a-C:N/Hole Transport Layer (HTL)/ Emitting Layer (EL)/Electron Transport Layer (ETL)/Al. As a hole transporting layer (HTL) a thin film of 1-(3-methylphenyl)-1,2,3,4 tetrahydroquinoline – 6 – carboxyaldehyde-1,1′-diphenylhydrazone (MTCD) was used. Tris(8-hydroxyquinoline aluminum) (Alq3) was used as electron transporting layer (ETL). For all devices with a-C:N buffer layer a significant increase in the electroluminescence intensity was observed compared to the conventional ITO/MTCD/EL/Alq3/Al structure. The results are interpreted in terms of a highly efficient balanced electron-hole injection into the emitting layer, because of an increase in the barrier height for the hole injection from the ITO. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)