Synthesis,Properties And Application In OLEDs Of Thermal Cross-linkable Triphenylamine Based Hole-transporting Materials

In this thesis,a series of thermal cross-linkable hole-transporting monomers with triphenylamine and tetraphenylbiphenylenediamine as the core and vinyl as the active group named as tri?4-vinylphenyl?amine?V-TPA?,N,N-di?phenyl?amine N'N'-bis?vinylphenyl?-1,1'-diphenyl-4,4'-diamine?V-p-TPD?and N,N,N',N'-tetra?p-vinyl phenyl?-1,1'-diphenyl-4,4'-diamine?V-TPD?with triphenylamine and tetraphenyl biphenylenediamine as the core and vinyl as the active group were designed and synthesized.The target product has good solubility in common solvents like tetrahydrofuran,chlorobenzene and toluene.The structures of the intermediate and target products were characterized by mass spectrometry and nuclear magnetic resonance spectroscopy.The temperature at which the hole-transporting monomer cross-links reacts closely relate with its thermal properties.Differential scanning calorimetry analysis showed that there are strong exothermic peaks at 150°C for all three hole transporting monomers,indicating that cross-linking reaction can occur at this temperature.By testing the resistance of cross-linked films prepared under different conditions to common solvents?chlorobenzene,tetrahydrofuran,toluene,etc.?,the conditions for complete cross-linking of the three monomers were determined:V-TPA and V-p-TPD150°C crosslinking for 0.5 h;V-TPD 160°C cross-linked for 0.5 h.A hole-transporting film with excellent solvent resistance was obtained.The UV-vis spectra before and after cross-linking indicate that the cross-linking process does not affect the photophysical properties of the compounds.Electrochemical studies have shown that the HOMO level of the compound is around-5.20 eV and can be used as a hole transport material in electroluminescent devices.The study of surface morphology and crystallization behavior of cross-linked films showed that the root mean square roughness of the cross-linked films is less than 0.5 nm,which has good flatness and morphology stability,even after high temperature annealing treatments.The carrier transport properties were studied by the space charge confinement current method.The hole mobility?of all the three materials are beyond 10^-55 cm²?V^-1?s^-1,which exhibited a good hole-transporting property.V-p-TPD was used as the monomer,and the hole-transporting monomer coating was prepared by spin coating method.After drying,the hole-transporting layer was cross-linked at 150°C to prepare undoped fluorescent OLED device.The double-layer device ITO/HTM/Alq₃/CsF/Al with evaporated Alq₃ as the light-emitting layer exhibits a lower light-on voltage?3.6 V?,a higher light-emitting luminance?12109 cd/m²?and higher current efficiency?5.50 cd/A?than the device on which the TPD thin film is evaporated.Moreover,the electroluminescence spectrum remains stable as the operating voltage increases;All-solution device ITO/PEDOT/HTM/PF-BT8/CsF/Al,with spin-coated PF-BT8 as the light-emitting layer was fabricated.The device with a cross-linked hole-transporting layer has a maximum current efficiency of 4.12 cd/A,whose efficiency is three times than the device without the hole-transporting layer.The results show that the thermally cross-linked hole-transporting monomer molecules have excellent process stability and device performance in the preparation of organic electroluminescent devices,especially full-solution processes.