High performance fluorescent and phosphorescent organic light-emitting diodes based on a charge-transfer-featured host material

Abstract Fluorescent and phosphorescent organic light-emitting diodes (OLEDs) were fabricated using a charge-transfer-featured compound, 6-{3,5-bis-[9-(4-t-butylphenyl)-9H-carbazol-3-yl]-phenoxy}-2-(4-t-butylphenyl)-benzo[de]isoquinoline-1,3-dione, as a host, and the electroluminescent (EL) characteristics of these two kinds of OLEDs were systematically studied. According to the photoluminescent quantum yields (ηpl), it was found that the external quantum efficiencies of both fluorescent and phosphorescent OLEDs were exceeding their theoretical limits. Based on the analysis of EL characteristics, the high device performance of fluorescent and phosphorescent OLEDs was attributed to both efficient energy transfer and triplet energy up-conversion, while direct exciton formation was also involved in phosphorescent OLEDs. In addition, the host film possessed high thermal and morphological stabilities due to the attachment of steric bulks on host molecule, resulting in the high doping concentration for both fluorescent and phosphorescent dyes. These results indicated that charge-transfer-featured material could be the promising host for both fluorescent and phosphorescent OLEDs.