Efficiency Roll-Off Optimization Of Organic Electroluminescent Devices Based On Thermal Activated Delayed Fluorescence Mechanism

The huge advantages of organic electroluminescent devices based on thermally activated delayed fluorescence?TADF?mechanisms have made researchers rush.It has a very promising future in the field of display and lighting.However,due to the application of TADF mechanism which in the field of organic electroluminescent devices is in its infancy stage,the organic electroluminescent devices based on thermally activated delayed fluorescent materials still have a series of key scientific problems that are waiting to be solved in the internal working mechanism and practical applications.In this paper,the research on the efficiency roll-off of blue and yellow light TADF devices is carried out,and the following research results are obtained.1)Based on the optimization of the blue light TADF device,the guest material is the material pBFCz-26DPPM synthesized by the laboratory master.The device structure is optimized by the adjustment of the host material,the optimization of carrier transport and injection,and the adjustment of the composite region,and use the p-i-n structure to further reduce roll-off.When the device structure is ITO/HATCN?10?/TAPC:HATCN?25?/TCTA?10?/DPEPO:5%pBFCz-26DPPM?20?/DPEPO?5?/TmPypb:2.5%LiQ?20?/LiQ?2?/Al,The highest current efficiency is 2.58 cd/A,the color purity is good,the 1931 color coordinate CIE_x,y is located at?0.15,0.08?,the device turn-on voltage is reduced,4.2V can illuminate the device,external quantum efficiency Significantly improved,reaching 4.3%,EQE reached 3.72%at 1000cd/m² brightness,and efficiency roll-off was only 13.5%.The roll-off of the device was much lower than the 38%roll-off of the device we just optimized.2)The second part is mainly to optimize the yellow light TADF device.The guest material is the TADF material 4CzTPN-Ph which is composed of Adachi project.Under the premise of the EL wavelength of 584nm,we first determine the spectrum by adjusting the doping concentration.then we reduce the roll-off of the device by optimizing the carrier transfer and injection and adjusting the position of the recombination zone.When the device structure is ITO/MoO₃?10?/TAPC?20?/MCP?10?/CBP:4CzTPN-Ph?4%,30?/TmPypb?30?/LiQ?2?/AL,the maximum external quantum efficiency is 10.66%,and EQE is 9.66%at5000 cd/m²,the efficiency roll-off is 13.1%,and the highest current efficiency is up to 30.5cd/A,the maximum power efficiency can reach 15.1lm/W,and the maximum brightness can reach 14000cd/m².Finally,we introduced the blue TADF material pBPCz-26DPPM as the main body of the device to improve the roll-off of the device.When the device structure is ITO/MoO₃?10?/TAPC?20?/MCP?10?/pBFCz-26DPPM:4CzTPN-Ph?2%,30?/TmPypb?30?/LiQ?2?/AL,the EL spectrum is at 584 nm,the turn-on voltage of the device is 5.2V,the maximum current efficiency is up to 20.2 cd/A,the maximum power efficiency is 9.32 m/W,and the maximum brightness is up to 12000 cd/m²,the maximum external quantum efficiency is 9.71%,At this time,the roll-off of the efficiency of the device from the maximum external quantum efficiency to 5000 cd/m² is only 12%,which is much lower than the 22.16%of the device roll-off when the experiment is not optimized,which basically achieves the experimental purpose.