Research On High Performance Non-Doped White Organic Light-Emitting Diodes Based On TADF Materials

White organic light emitting diodes(WOLEDs)have the advantages of high efficiency,high color quality,low cost and can be processed into flexible light-emitting devices,so they have attracted wide attention from the industry and academia in the field of lighting and display in the future.For the preparation of high-performance WOLEDs,to obtain higher efficiency from the manufacturing process,most of them use doping methods,but this undoubtedly increases the complexity and difficulty of the experiment.The undoped method can effectively simplify the experimental process,improve the experimental precision and make the device structure design more flexible.This method requires the selection or development of high-performance luminescent materials.Among them,thermally activated delayed fluorescence(TADF)materials have the advantages of superior luminescent properties,such as high efficiency,no heavy metal elements and low cost.In this paper,based on TADF materials,we will adopt the undoped method to solve the problems of low efficiency,high cost,high efficiency roll-off,low color rendering index(CRI)and complex device structure,the specific work is as follows:Firstly,the excellent TADF material DMAC-TRZ is used as the bluish-green emitter.By strategically inserting several red and yellow ultra-thin phosphorescent emitters between the bluish-green TADF emitter,the optimized hybrid WOLED showed a maximum external quantum efficiency(EQE)of 18.7%,and the EQE roll-off from maximum EQE to EQE at 1000cd/m~2 is only 7%.At the same time,a high CRI of 87 and a low color temperature(CCT)of 2759can be obtained at 1000 cd/m~2.Secondly,the bipolar TADF material DMAC-DPS is used as the interlayer to modulate the exciton distribution.The optimized monochromatic and white OLED exhibited maximum EQE of 18.1%and 15.6%,current efficiencies(CE)of 55.7 cd/A and 46.6 cd/A,as well as power efficiencies(PE)of 43.8 lm/W and 41.8 lm/W,respectively.More importantly,the devices adopted an ultrathin non-doped emissive layer architecture,and the thickness of the emissive layer was only 3.6 nm,which was beneficial to reduce costs and simplify preparation process.Finally,the TADF material Spiro AC-TRZ is used as the blue emitter,through inserting ultrathin orange phosphorescent emitters in the appropriate positions between blue bipolar TADF emitters,the optimized WOLED exhibited maximum EQE,PE and CE of 15.0%,47.4 lm/W and46.2 cd/A,and retained 14.7%,41.7 lm/W and 45.8 cd/A at a practical brightness of 1000 cd/m~2,and the device only decreased 2%from maximum EQE.In addition,the device also showed a low turn-on voltage of 2.5 V and a maximum brightness of 39810 cd/m~2.