EL Behavior for Blue-Emitting Aluminum Quinoline- Based Organic Light-Emitting Diodes

Abstract

We fabrucated bilayer organic light-emitting diodes (PLEDs) consisting of a diamine derivative (α-NPD) and aluminum(III) bis(2-methyl-8-quinolinate)4-phenylphenolate (BAlq) and investigated their EL properties depending on BAlq's thickness and a kind of cathode metal. Since the OLEDs showed EL spectra including both α-NPD and Balq₃ emissions, we discussed the recombunation mechanism of OLEDs from the ratio of α-NPD and Balq3 emissions. The α-NPD/Balq₃ OLEDs have two recombination zones in α-NPD and BAlq layer, so that electrons are injected into α-NPD layer. To our surprise, when Al with a poor electron injection is used as the cathode, α-NPD content was found to increase as compared with the use of LiF/Al in spite of decreasing electron current. Electron injection into α-NPD was thought to be one of degradation factors.