Synthesis And Properties Of Electron Barrier Materials Containing Triarylamine And Carbazole Structures

At present,Organic Light Emitting Devices（OLED）have shown great potential for application in full color displays.However,the performance of blue light OLED is relatively poor,making it difficult for OLED to meet commercial standards in the field of full color displays.Adding an auxiliary functional layer electronic barrier layer to OLED devices can achieve maximum recombination of charge carriers within the luminescent layer,effectively improving the device’s luminous efficiency and device lifespan.In this paper,three electron barrier materials EB1,EB2 and EB3 containing triarylamine and carbazole structure were synthesized by Suzuki coupling reaction,Buchwald Hartwig coupling reaction and other common reactions,and their structures were confirmed and characterized by mass spectrometry,¹H NMR,¹³C NMR and other techniques.The photoelectric physical properties of the synthesized electron barrier materials were studied,including energy level,UV spectrum,fluorescence spectrum,electrochemical stability and thermal stability.It is found that the three compounds have appropriate highest occupied molecular orbital（HOMO）energy levels,lowest unoccupied molecular orbital（HOMO）energy levels and triplet energy levels,which are conducive to the injection of holes and can effectively block the further diffusion of excitons,and can be used as electronic barrier materials;The UV visible maximum absorption peak wavelength of the compound is about 350 nm,indicating that the compound molecule has a largerπ-πconjugated system,which is conducive to the hole dissociation and transport;The fluorescence emission peak of the compound is in the range of 420 nm to 430 nm,located in the wavelength range of blue light（390 nm to 450 nm）,so it can be applied in blue light OLED devices;Through cyclic voltammetry,it is found that the three compounds all have high chemical stability,which has great advantages for the preparation of highly stable OLED devices,and is conducive to maintaining the stable shape of OLED devices during long-term operation;The thermal stability of the compounds was tested and it was found that the glass transition temperatures of the three compounds were relatively high,all between 130℃and 145℃,exhibiting good thermal stability and facilitating the vacuum evaporation of materials into stable electron barrier layer films.The compound was vacuum evaporated into an electron barrier layer thin film and a blue OLED device with this electron barrier layer structure was prepared.The influence of electron barrier layers with different thicknesses and materials on the electrical performance of OLED devices was studied by testing the electrical performance of the devices.In this article,OLED devices with different thicknesses of electronic barrier layers were first tested,and the effects of different thicknesses of electronic barrier layers on the luminescence efficiency and device life of OLED devices were studied.It was found that compared to OLED devices with 5 nm and 20 nm electronic barrier layers,devices with 10 nm electronic barrier layers exhibited low driving voltage,high luminescence efficiency,and long service life.Under the same applied voltage,when a blue OLED device uses a 10 nm thick electron barrier layer,the device has the lowest startup voltage,maximum current density,and luminescence brightness,while also having a relatively long service life.This is due to the addition of an electron barrier layer in the device,which on the one hand reduces the energy barrier for holes to be injected from the hole transport layer into the luminescent layer,which is conducive to hole injection;On the other hand,it blocks the further transmission of electrons within the luminescent layer,allowing holes and electrons to achieve maximum recombination within the luminescent layer,resulting in the device having maximum luminescence brightness.Then the device performance of different electron barrier materials is characterized and compared.It is found that under the same thickness of the electron barrier layer,the material EB2 with higher triplet energy level and the largest conjugated area is used as the electron barrier layer,and the luminous efficiency and device life of the device have significantly improved,and the device performance is optimal.