Electroluminescence was observed for the layered structures containing the transparent anode of the indium-tin oxide (ITO), organic hole-transporting layer, luminescence layer of one of the studied complexes, and the metallic cathode of Al:Ca (5%) alloy. The hole-transporting materials used were triaryl derivatives - well-known naphthyl-substituted benzidine derivative (NPD) and the oligomer of triphenylamine oligo(4,4'-(4''-methyl)triphenylamine) (PTA) [22
]. The carbazol derivative 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP) and poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) were also used for forming the hole-transporting layer. The structures of these compounds are shown in Figure . All the materials are characterized by blue PL 450 to 470 nm [18
]. Zinc complexes and PTA were synthesized as described elsewhere [18
]. NPD, CBP, and PEDOT:PSS were supplied by Aldrich (Sigma-Aldrich Rus LLC, Moscow, Russia). All the organic layers in the OLED devices (except PTA and PEDOT:PSS) were prepared by vacuum evaporation. PTA and PEDOT:PSS were spin casted from toluene and aqueous solutions, respectively. The EL and PL spectra were measured with the Ocean Optics fiber optics spectrometers QE65000 or PC1000 (Eurolase Ltd., Moscow, Russia). LED with λ
= 370 nm was used to excite the PL.
We have prepared and measured the EL spectra of the following OLED devices based on zinc complexes with sulphanilamino-substituted ligands.
device 1: ITO/PTA/NPD/Zn(PSA-BTZ)2/Al:Ca
device 2: ITO/PTA/Zn(PSA-BTZ)2/Al:Ca
device 3: ITO/PTA/NPD/CBP/Zn(PSA-BTZ)2/Al:Ca
device 4: ITO/PTA/CBP/Zn(PSA-BTZ)2/Al:Ca
device 5: ITO/PEDOT:PSS/Zn(PSA-BTZ)2/Al:Ca
device 6: ITO/PTA/NPD/Zn(TSA-BTZ)2/Al:Ca
device 7: ITO/PTA/Zn(TSA-BTZ)2/Al:Ca
device 8: ITO/PTA/NPD/Zn(POPS-BTZ)2/Al:Ca
device 9: ITO/PTA/NPD/CBP/Zn(POPS-BTZ)2/Al:Ca
device 10: ITO/PTA/NPD/Zn(DFP-SAMQ)2/Al:Ca
device 11: ITO/PTA/Zn(DFP-SAMQ)2/Al:Ca
In some devices, both PTA and NPD deposited in succession were used as materials for hole-transporting layers. In any case, the EL spectrum of the device is determined by the hole-transporting material, which is in contact with the zinc complex. The devices are typically characterized by bias voltages of light appearance about 2.5 to 3 V and brightness of 103 cd/m2 at 10 V.