High-efficiency blue-emitting organic light-emitting devices with 4, 4′, 4″-tris(N-carbazolyl)-triphenylamine as the hole/exciton- blocking layer

Organic light-emitting devices with the structure of indium-tin-oxide (ITO)/4, 4′, 4″-tris(N-carbazolyl)-triphenylamine (TCTA, with different thicknesses)/2-pyrenyl-9-phenyl-9-pyrenylfluorene (2P9PPF) (30 nm)/bathocuproine (BCP) (40 nm)/Mg : Ag (250 nm) have been investigated. The effect of the TCTA layer on the performance of blue-emitting devices has been studied. It is demonstrated that the inserted 8 nm thick TCTA layer neighbouring the anode of the device leads to the efficiency and luminance increasing ten times, reaching 3.8 cd A^-1 at 9 V and 17 000 cd m^-2 at 15 V, respectively. It is suggested that the inserted TCTA layer acts as an effective exciton-blocking layer, and also plays the role of the anode buffer layer.