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

We fabrucated bilayer organic light-emitting diodes (PLEDs) consisting of a diamine derivative (alpha-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 alpha-NPD and BAlq3 emissions, we discussed the recombunation mechanism of OLEDs from the ratio of alpha-NPD and BAlq3 emissions. The alpha-NPD/BAlq3 OLEDs have two recombination zones in alpha-NPD and BAlq layer, so that electrons are injected into alpha-NPD layer. To our surprise, when Al with a poor electron injection is used as the cathode, alpha-NPD content was found to increase as compared with the use of LiF/Al in spite of decreasing electron current. Electron injection into alpha-NPD was thought to be one of degradation factors.