Luminance and charge transport mechanisms for phosphorescent organic light-emitting devices fabricated utilizing a tris(2-phenylpyridine)iridium-doped N,N′-dicarbazolyl-3,5-benzene emitting layer

Abstract

The luminance and the charge transport mechanisms for phosphorescent organic light-emitting devices (PHOLEDs) fabricated utilizing a tris(2-phenylpyridine)iridium (Ir(ppy) 3)-doped N,N′-dicarbazolyl-3,5-benzene (mCP) emitting layer (EML) were investigated to improve the luminance efficiency of PHOLEDs. When Ir(ppy) 3 molecules existed on the electron transport layer (ETL) side of the EML, the current density of the PHOLED with an mCP EML containing an Ir(ppy) 3-doped thin layer increased. The Ir(ppy) 3-related electroluminescence (EL) intensity of the PHOLEDs with an Ir(ppy) 3-doped EML increased with increasing operating voltage. The increase in the current density was due to the lowest unoccupied molecular orbital levels of the Ir(ppy) 3 and the 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline ETL being identical, and the increase in the EL intensity could be attributed to a movement of the recombination zone to the center of the EML due to an increase in the electron injection from the ETL into the EML at high voltages.