Electroluminescent Properties of Organic Light-Emitting Diodes with Blue-Emitting Alq

Aluminum(III) bis(2-methyl-8-quinolinate)4-phenylphenolate (BAlq) is well-known to be a hole blocking material against phosphorescent light-emitting diodes. The authors investigated the EL mechanism of BAlq. The PL intensity of BAlq was stronger than that of Alq3, but the EL performance of BAlq LED was poorer than that of Alq3 LED because of lower electron injection. The introduction of Alq3 electron injection layer improved EL performance, but EL decreased with decreasing BAlq thickness beyond the optimal Alq3 thickeness. The authors clarified by doping method that the recombination zone of BAlq/Alq3 LED is located near the interface between BAlq and Alq3 and Alq3 may act as quencher to BAlq.