Combinatorial fabrication and studies of 4,4'-bis(9-carbazolyl) biphenyl (CBP)-based UV-violet OLED arrays

摘要

Arrays of UV-violet [indium tin oxide (ITO)]/[copper phthalocyanine (CuPc)]/[4,4'-bis(9-carbazolyl) biphenyl (CBP)]/[2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (Bu-PBD)]/CsF/Al organic light-emitting devices (OLEDs), fabricated combinatorially using a sliding shutter technique, are described. Comparison of the electroluminescence spectrum with the photoluminescence spectrum of CBP indicates that the emission originates from the bulk of that layer. However, due to the high gap of CBP and the strong hole capture cross section of perylene contaminants, it was difficult to completely eliminate the emission from the latter. In arrays of devices in which the thickness of the CuPc and Bu-PBD were varied, but that of CBP was fixed at 50 nm, the optimal radiance R was obtained at CuPc and Bu-PBD thicknesses of 15 and 18 nm, respectively. At 10 mA/cm~2, R was 0.38 mW/cm~2, i.e., the external quantum efficiency was 1.25%; R increased to ～1.2 mW/cm~2 at 100 mA/cm~2.