Aggregation-Induced Delayed Fluorescent Material Based On Host Materials For The Application In Organic Light-Emitting Diodes

Organic light-emitting diodes?OLED?,as an important display technology,have the advantages of self-luminous,low power consumption,fast response,wide viewing angle,etc.,and have attracted widespread attention from researchers.In order to improve exciton utilization and reduce costs,thermally activated delayed fluorescence?TADF?materials are widely used in OLED devices.However,traditional TADF luminescent materials are prone to problems such as aggregation caused luminescence quenching and efficiency roll-off,which greatly limits the process of OLED commercialization.In order to break this barrier,this paper researches on the aggregation-induced delayed fluorescence?AIDF?materials based on the host material and its application in OLED.These materials emit light weakly in the solution state and has no delayed fluorescence phenomenon,but emits strong light in the aggregated state with obvious delayed fluorescence phenomenon.The highly distorted molecular configuration is conducive to improving the above problems of traditional TADF materials.Based on this,the specific research content is as follows:In Chapter 2,we synthesize and characterize a series of new AIDF materials DCB-BP-PXZ,CBP-BP-PXZ,m CP-BP-PXZ and m CBP-BP-PXZ.The molecular design concept is to combine the DCB,CBP,m CP and m CBP dicarbazole host materials with AIDF moiety,and the prepared device can be considered as a self-doped device.Their films have high photoluminescence quantum yield?PLQY?.They can also make full use of singlet and triplet excitons and suppress exciton annihilation at high voltages.These four molecules have prominent AIDF characteristics.These non-doped OLEDs based-on AIDF molecules show high brightness(?100000 cd m^?2),excellent external quantum efficiency(?_ext)?22.1%-22.6%?,and the efficiency roll-off at 1000 cd m^?2 is negligible.Non-doped OLED device using DCB-BP-PXZ as the light-emitting layer has the best performance.The maximum?_ext and current efficiency??_C?are up to 22.6%and 72.90 cd A^-1,respectively,and the efficiency roll-off is extremely small.These are the most effective non-doped OLED devices reported at the time.In Chapter 3,we designe and synthesize three compounds containing fluorene-based hole-transporting host materials and AIDF moiety?DCDMF-BP-PXZ,DCDPF-BP-PXZ and DCSBF-BP-PXZ?.DCDMF,DCDPF and DCSBF containe fluorene and biscarbazole groups,and the rigidity and bulkiness of the molecule is enhanced by the introduction of dimethyl,diphenyl,and fluorene.All three luminescent molecules show apparent AIDF characteristics.Through the analysis of the crystal structure and packing mode of the three molecules,it is found that small differences in geometric structure has a great impact on their photophysical properties and electroluminescence?EL?properties.The molecular conformation and molecular packing have significant impact on PLQY values,and thus result in differences in EL properties.Non-doped OLED devices based on DCDMF-BP-PXZ and DCDPF-BP-PXZ achieve high?_ext of up to 19.0%and 24.4%,respectively,and the efficiency roll-off at 1000 cd m^?2 is very small.In Chapter 4,we designe and synthesize two new AIDF materials TCTA-BP-PXZ and TCTA-BP-DMAC with bipolar carrier transport properties.TCTA is usually used as a hole transporting layer and exciton blocking layer owning to excellent hole transporting ability and high triplet energy level.Both molecules have noticeable AIDF properties.The carrier transport ability of these material is relatively balanced,and it has excellent bipolar carrier transport characteristics.Vacuum-deposited non-doped and doped OLED devices using TCTA-BP-PXZ as the light emitting layer exhibit high?_ext of 16.9%and 17.6%,respectively,and the efficiency roll-off at 1000 cd m^?2 is very small.In addition,solution-processed non-doped devices based on TCTA-BP-PXZ and TCTA-BP-DMAC show yellow light and sky-blue light,respectively,with?_ext of 10.7%and 9.8%,respectively.This work proves that AIDF luminescent molecules have good application potential different kinds of OLED devices.