Study Of Fabrication And Properties On Efficient Yellow And Full Fluorescent White OLEDs Based On Delayed Fluorescence Materials

White organic light-emitting diodes(WOLEDs)have a bright application prospect in the display lighting industry.Phosphorescent WOLEDs have high cost and potential heavy metal contamination due to the use of precious metals in the fabrication process.Recently,more and more researchers have paid attention to the research of all fluorescent WOLEDs based on thermally induced delayed fluorescence(TADF)materials.In order to construct an efficient two-color full fluorescent WOLED,good yellow and blue emitters are needed.This thesis focuses on the study of properties mechanism of yellow devices based on delayed fluorescence and their applications in all fluorescent WOLEDs.The detailed content is as follows:1.Two yellow TADF emitters 34AcCz-PM and 34AcCz-Trz were selected to construct a series of yellow devices from low to high doping concentration with host material CBP,and the effects of trap capture mechanism and energy transfer mechanism on the properties of different types of TADF devices were analyzed simultaneously.And TADF host material 3Cz Php PM instead of CBP was selected to construct devices for further optimize the properties of yellow devices.Then blue material 3Cz An Bzt were selected to construct full fluorescent WOLEDs combining with yellow materials,respectively.The WOLED based on 34AcCz-PM as a yellow emitter achieved an external quantum efficiency(EQE)of 15.5%,with a color coordinate(CIE_x,y)of(0.30,0.47).The WOLED based on 34AcCz-Trz as a yellow emitter achieved an EQE of 11.1%,a CIE_x,y of(0.31,0.48)was obtained simultaneously.2.A series of sensitized yellow devices were constructed by using two yellow TADF materials 34AcCz-PM and 34AcCz-Trz as sensitizers,the traditional yellow fluorescence material TBRb as the emitter,and the traditional material CBP and TADF material3Cz Php PM as the hosts.The sensitized device based on 3Cz Php PM:3%34AcCz-Trz:0.5%TBRb as emitting layer achieved the EQE of 19.1%with small roll-off.The sensitized structure of 3Cz Php PM:3%34AcCz-Trz:0.5%TBRb was used as yellow layer,and combined blue material 3Cz An Bzt to construct efficient WOLEDs.The best WOLED achieved an EQE of 14.8%and a CIE_x,y of(0.42,0.47).Moreover,the brightness of the device was more than 50000 cd/m²,the stability of device was relatively efficient with the EQE of 14.5%at 1000 cd/m²,and the EQE of 13.1%at 5000 cd/m².