Amorphous carbon nitride thin films as electron injection layer in organic LEDs

Thin films of a-C:N and a-SiC:N deposited by diode r.f. sputtering and magnetron sputtering, respectively, were used as electron injection layers in organic light emitting diodes. The devices consist of two different heterojunction structures: the first one, indium tin oxide (ITO)/hole transport layer (HTL)/electron transport layer (ETL)/a-C:N/Al and the other one formed by ITO/HTL/ETL/a-SiC:N/Al. The HTL was obtained using a thin film of 1-(3-methylphenyl)-1,2,3,4 tetrahydroquinoline-6-carboxyaldehyde-1,1'-diphenylhydrazone (MTCD), while the tris(8-hydroxyquinoline aluminum) (Alq3) is used as ETL. For all produced devices a significant increase in the current compared to the conventional ITO/MTCD/Alq3/Al structure was observed. Light emission was detected in both ITO/MTCD/Alq3/a-C:N/Al and ITO/MTCD/Alq3/a-SiC:N/Al structures. The results are interpreted in terms of a highly efficient electron injection from the carbon nitride layer into the electron transporting one. The electroluminescent spectra of the devices are also reported and discussed