Study On Materials And Devices With Thermally Activated Sensitized Fluorescence

Thermally activated sensitized fluorescence(TSF)utilizes thermally activated delayed fluorescence(TADF)hosts for conventional fluorescent dopants(CFD),where the host harvests triplet(T₁)through reverse intersystem crossing and then transfers the energy via F(?)rster energy transfer(FET)to CFD for emitting.Benefitting from high exciton utilization of TADF host and high luminous efficiency as well as high color purity of CFD,TSF has attracted much attention.However,there is still excitons loss in the TSF,which makes it difficult to improve the device efficiency.This doctoral dissertation studies the problem based on molecular design and device structure optimization.Here,the exciton loss pathway of Dexter energy transfer(DET)from the TADF host to the CFD in TSF system is revealed and then the molecular design strategy that the introduction of inert steric hindrance groups at the periphery of molecule to inhibit DET is proposed.Further,the strategy multi-channel sensitized fluorescence that suppresses DET and enhances FET at the source is brought up.With the above strategies,efficient TSF device with high color purity is successfully prepared.A novel way for designing high-performance fluorescent devices is put forward,promoting the industrialization process of TSF.Details as follows:1.Dopants and hosts with inert steric hindrance group as well as devices:DET requires close contact and efficient molecular orbital overlap between the energy donor and the energy acceptor.CFDs and hosts with different sizes of steric hindrance groups on the periphery are designed and synthesized to manipulate DET.Here,the energy loss pathway of DET from TADF host to CFD in TSF is revealed and then molecular design strategy of introducing peripheral inert steric hindrance groups to inhibit DET during transfer process is proposed,resulting in 45%promotion of device efficiency.2.Materials and devices with multi-channel sensitized fluorescence:Multiple reverse intersystem crossing regulates the exciton dynamics on the TADF materials with TADF host,achieving the highest external quantum efficiency(EQE)of 24.8%at 10000cd m^-2 among all green devices based on TADF emitters reported in the literature.The conclusion that multiple reverse intersystem crossing can transfer T₁ into S₁ efficiently is drawed.Furthermore,this work introduces multiple reverse intersystem crossing into the TSF and proposes the strategy multi-channel sensitized fluorescence to suppress DET and enhance FET at the source.Subsequently,the formation and advantages of multi-channel sensitized fluorescence is proved.Finally,TSF device with EQE>23%firstly is achieved.3.Dopants with high color purity and devices:The lack of narrow-spectrum CFD and easily trapped carriers on the CFD thus poor performance limits sensitized fluorescence device with high-efficiency and high-color purity.Based on classic fluoroboron dipyrrole,a novel CFD was developed by introducing an inert steric hindrance group on its periphery.With multi-channel sensitized fluorescence by adjusting the carrier recombination position,efficient sensitized fluorescence device with high color purity is successful prepared,achieving full-width-at-half-maximums only 32 nm and EQE up to 19.0%.