Metallophthalocyanine films as hole-transport layer in organic light-emitting devices

Electroluminescence (EL) characteristics of the double-MPc-layered devices consisting of ITO/MPc1/MPc2/Alq3/Mg–Ag were investigated, where MPc1 and MPc2 represent two metallophthalocyanines and Alq3 stands for tris(8-quinolinolato)aluminum(III). A compatible double-MPc-layered structure led to a decreased hole-injection barrier at the ITO/MPc1 interface and an increased electron-blocking ability of the MPc2 layer in the device. The EL efficiency of the device was improved further by using a 4,4′-bis(m-tolyphenylamino) biphenyl (TPD) layer as an additional hole-transport layer due to its good electron-blocking ability. For the double-MPc-layered devices with a TPD layer, the EL performances were dependent primarily on the electronic structure of ITO/MPc1 interface rather than that of MPc1/MPc2 or MPc2/TPD interface.