The Study Of Performance Of Phosphorescent OLED Devices Based On Host-guest Dopant System

Organic light-emitting diodes?OLED?can be used in high-quality flat panel displays and lighting fields for several advantages,including their self-luminous,small size,good color development,flexibility,and low cost.Numerous researchers choose phosphorescent materials with high efficiency to obtain higher performance OLED devices.However,there are still many problems in the efficiency,stability and cost of phosphorescent OLED devices.To solve the above problems of the phosphorescent OLED devices,this work studied the effect of optimization of the doped emitting layer on the device performance and emission mechanism of phosphorescent OLED devices.By selecting suitable host-guest dopant system,optimizing the guest dopant ratio and doping thermal activated delayed fluorescence?TADF?materials,the energy transfer process and charge transfer of the emitting layer can be optimized to improve the performance of phosphorescent OLED devices.The specific research content is divided into three parts:Firstly,three different host materials CBP,26DCzPPY and mCP doped guest phosphorescent fac-Ir?ppy?₃ were selected as the emitting layer to study the effect of emitting layers of different hosts on device performance.The experimental results showed that three host devices had high device performance,and compared with CBP device and 26DCzPPY device,the maximum current efficiency?CE?and the maximum external quantum efficiency?EQE?of mCP device have been greatly improved,reaching82.12 cd/A and 23.8%,respectively.By analyzing the structure of the devices,the energy transfer characteristics in the emitting layer and the electrical characteristics of single carrier devices with emitting layers of different hosts,we find that excellent device structure design is the main reason for the high performance of three devices,and the higher performance of the mCP device is attributed to better energy transfer process and better charge balance of the emitting layer with mCP.Secondly,the emitting layer with mCP served as the host and fac-Ir?ppy?₃ served as the guest was used to fabricate phosphorescent OLED devices with different dopant concentrations,the effect of dopant concentration on the luminescent performance and emission mechanism of the device was systematically studied.By optimizing the dopant concentration,we obtained an optimum device with maximum CE of 84.71 cd/A and maximum EQE of 24.5%at 5wt%dopant concentration.At the same time,the emission mechanism of the dopant system was discussed in detail,and the specific relationship between dopant concentration and emission mechanism and the reasons for the change of device performance are revealed through analyzing the characteristics of electroluminescence?EL?spectra and transient EL spectra of the device.Finally,the low concentration of TADF material DMAC-DPS was used to optimize the emitting layer of host-guest system,the effect of low concentration of TADF on phosphorescent OLED device performance was studied.When the concentration of DMAC-DPS was 1wt%,the driving voltage of the device was only 3.3 V at 1000 cd/m²,the maximum power efficiency?PE?and EQE could reach 65.44 lm/W and 18.2%,and the operation lifetime was 4 times longer than that of the device without doping DMAC-DPS.Compared with the device without doping DMAC-DPS,the efficiency and lifetime of the DMAC-DPS device were remarkably improved,the result indicated that DMAC-DPS could effectively improve the performance of phosphorescent devices.We believe that the better device performance can be attributed to the optimization of the energy transfer process in the emitter layer and lifetime of phosphorescent triplet excitons by DMAC-DPS.In summary,this work studies the influence of optimizing the emitting layer of phosphorescent OLED device on device performance,and provides some ideas for the fabrication of simple,high efficiency and long-lifetime OLED devices.