Design And Synthesis Of Novel OLED Host Materials With High Triplet Energy Levels

In the past three decades,organic light-emitting diodes(OLEDs)have attracted great attention due to their advantages of thinness,flexibility,self-luminescence,and fast response.However,the performance of blue OLEDs is still unsatisfactory.The main reason is that the blue OLED material has a high triplet energy levels,which requires the host material with higher triplet energy level to sensitize it.However,at present,the host materials with high triplet energy levels as well as excellent thermal stability are still lacking,which limits the further development of OLED technology.To solve this problem,in this paper,we designed and synthesized two kinds of OLED host materials with higher triplet energy levels and studied their applications in blue OLED devices.The specific research contents are as follows:(1)Four OLED host materials based on carbazole and carbazole derivatives were designed and synthesized,and blue OLED devices were prepared as well.The carbazole and 1,8-dimethylcarbazole groups were attached to the benzene ring,pyridine and pyrimidine to synthesize PhMe-2Cz,Pra-2MeCz,Prm-2MeCz and Prz-2MeCz.All these host materials exhibited good thermal stability and high triplet energy levels.Except for PhMe-2Cz,the triplet energy levels of other three materials have reached to 3.0 eV or even higher,and the decomposition of four materials are 363 °C,388 °C,408 °C,409 °C.Among the OLED devices based on the four host materials,the devices based on Pra-2MeCz and Prm-2MeCz have higher device efficiency,the maximum EQE in the TADFOLED device have reached to 18.7% and 16.0%,the EQE of the blue phosphorescent devices have reached to 19.3% and 17.5%.The high device efficiency indicates the feasibility of our experimental design.(2)Two novel host material based on acridine were designed and synthesized and their application in electroluminescent devices was studied as well.In this work,we combined the donor acridinyl group with the pull-electron pyridine and pyrimidine groups to synthesized two host materials Pra-2DMAC and Prm-2DMAC.These two materials have high thermal stability and their decomposition temperatures are 379 °C and 387 °C,respectively.In addition,both of them have a highe triplet energy level of 3.11 eV and 3.07 eV,respectively.In TADF-OLED devices,we made these two host materials to sensitize the blue TADF material 2CzPN,the maximum external quantum efficiency of the device was 15.9% and 12.2%,respectively,and the FIrpic based PHOLEDs hosted by Pra-2DMAC and Prm-2DMAC exhibited high device performance with maximum external quantum efficiencies(EQEs)of 17.8% and 17.4%,respectively.Two types of OLED host materials were designed and synthesized in this paper and they have high triplet energy levels as well as good thermal stability,not only they can be used to sensitize blue TADF materials,but also can be used to sensitize blue phosphorescent materials.And this can alleviate the state of lack of blue OLED host materials and promote the development of blue OLED technology.