Design,Preparation And Performance Of Organic Light-emitting Electrochemical Cells Based On Thermally Activated Delayed Fluorescence

Light-emitting electrochemical cell(LEC)is a new type of electroluminescent device which has attracted attention because of its simple architecture,low driving-voltage,easy-to fabrication,and has a wide variety of new application in the fields of wearable devices,medicine,sensors,lighting displays and so on.Thermally activated delayed fluorescence(TADF)material is a new type of luminescent material that spatially separates the highest occupied molecular orbital(HOMO)and the lowest unoccupied molecular orbital(LUMO)to have a very small single-triplet energy gap(?E_ST).It enables the conversion of triplet excitons to singlet excitons via antisystemic scramble(RISC),and finally the singlet excitons back to the ground state for luminescence,effectively improving exciton utilization.Thermally activated delayed fluorescence(TADF)compound is a new type luminescent material because they do not use rare metals and they are easy to synthesize.Therefore,in this paper,based on the solution-processed TADF-LEC,the photophysical properties,electrochemical properties,and electroluminescence performance of the host compounds and luminescent materials were studied.The main research results are as follows:1.The photophysical properties,electrochemical properties and electroluminescence performance of TADF material BPAPTC were studied,and BPAPTC was doped into PVK:OXD-7 blend host to achieve efficient host-guest energy transfer.Compared with the classic TADF small molecule 4CzIPN,the photophysical and electroluminescence characterizations showed that with the doping concentration increasing,the intermolecular ACQ effect led to severe exciton quenching,significant red shift in the spectrum,and the device performance was low.Due to through-space charge transfer(TSCT)effect,BPAPTC suppressed aggregation-caused quenching(ACQ),achieved efficient host-guest energy transfer at high doping concentration,and obtained green TADF-LEC devices with high luminance and high efficiency,which was higher than the reported performance of TADF-LEC devices,with a maximum EQE of 7.67%.Besides,this work also further reveals the mechanism of dual channel TADF-LEC with high doping concentration of the guest compounds,which provides a new idea for the device design of efficient LEC.2.It was found that using a host-guest hybrid system,the host compound provides matching p-type/n-type doping capability to form stable p-i-n junction during in situ electrochemical doping,ensuring effective electron-hole transport.In this work,Sim CP2,OXD-7 and Sim CP2:OXD-7 blend host were used as the host materials and the polymer TADF molecule PABPC was used as the light-emitting material.To study the photophysical properties,electrochemical properties,morphologies and device performance of TADF-LEC device with three different host compounds by optimizing the composition structure of the host compounds.Due to weak electrochemical doping capability and rough morphology,single-host device suppressd exciton transport,resulting in poor device performance.On the other hand,The device with Sim CP2:OXD-7 blend host achieved balanced electron-hole transport,exhibits good stability,and prepares devices with smooth shape and high efficiency performance.Moreover,the maximum external quantum efficiency is 2.24%and the maximum current efficiency reaches 6.89 cd A^-1.