High efficiency and color saturated blue electroluminescence by using 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl as the thinner host and hole-transporter

A traditional hole-transporting (HT) material, 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB) was used as the host to fabricate a blue organic light-emitting diode (OLED) in which the blue dopant emitter is 2,5,8,11-tetra-t-butyl-perylene (TBP) and the another NPB layer adjusted to thinner host was also used as the HT-layer. The blue electroluminescent (EL) was proved to be originated from the narrower doped layer and the adjacent NPB HT-layer. Compared with the previous blue EL devices based on TBP dopant, the performances of the blue OLED were improved by using a thinner NPB host layer. The blue OLED shows higher efficiency and better blue color saturation, such as the device behaving a maximum efficiency of 4.6 cd/A, CIE color coordinates of x = 0.136 and y = 0.173 at a bias of 5 V, and a peak luminance of 11,500 cd/m2 at a bias of 20 V. The operation mechanism of the blue device was also discussed.