Organic light-emitting diodes with improved hole-electron balance by using copper phthalocyanine/aromatic diamine multiple quantum wells

Organic light-emitting diodes (OLEDs) with multiple-quantum-well structures, which consist of copper phthalocyanine and ${\mathrm{N,N}}^{\prime }$ -bis-(1-naphthyl)-${\mathrm{N,N}}^{\prime }$ -diphenyl-${\text{1,1}}^{\prime }$ biphenyl 4, $4^{\prime }$ -diamine, have been fabricated. The effect of the MQW structure upon the performance of OLEDs with tris(8-hydroxyquinoline) aluminum as the emitting material has been investigated. Compared with the luminous efficiency of the conventional diode with the MQW number of 0, that of the diode with the MQW number of 4 has been sharply increased up to 10.8 cd/A. Such an improvement in the device performance was attributed to the improved hole-electron balance, which can be further attributed to the introduction of the MQW structure.