A Study On Properties Of Sensitized Organic Electroluminescent Devices

Fluorescent materials,which are metal-free with tunable,ultrafast,and very stable emission,are of significant importance for commercial organic electroluminescent devices(OLED).However,due to only 25% of electronically excited excitons in singlet states are available,the device efficiencies of FOLEDs are usually much lower then that of phosphorescent OLEDs(PhOLEDs).Therefore,in order to harvest triplet excitons and improve the efficiency of FOLED,the new mechanism that use thermally activated delayed fluorescence(TADF)and hybridized local and charge-transfer(HLCT)with high exciton utilization as host sensitizers has shown potential to achieve 100% exciton utilization.This paper focuses on the application of host materials with high exciton utilization in fluorescent OLED devices,improving the efficiency of fluorescent devices and contributing to the industrialization of OLEDs.(1)Three thermally activated delayed fluorescence(TADF)materials were used: PXZ-DPS,2PXZ-TAZ and 2PXZ-OXD as the host sensitizing fluorescent material,respectively.When using PXZ-DPS as the host,the maximum current efficiency and external quantum efficiency of the thermal activation sensitized fluorescence(TASF)device were 23.4 cd/A and 6.9%,respectively.By reasonably selecting the TASF host material,the exciton utilization of the FOLED device can be exceeded by a 25% limit,and an external quantum efficiency of more than 5% is obtained.(2)A TADF material DMAC-DPS was used as host and PXZ-DPS was used as second component sensitizing fluorescent material.The system utilizes a high triplet level and a wide band gap to form an effective energy ladder,thereby utilizing the high exciton utilization of the two TADF materials by F?rster energy transfer.The maximum current efficiency,power efficiency,and external quantum efficiency of the device were 34.2 cd/A,21.4 lm/W,and 11.1%,respectively.(3)The high-efficiency green FOLED is prepared and optimized with a hybridized local and charge-transfer(HLCT)material TPMCN also having high exciton utilization.This approach,similar to TASF,does not need heavy metal complexes,and the device structure is simple.Maximum external quantum efficiency and external utilization efficiency of these HLCT-SF OLEDs are up to 6.3 and 64%,respectively,apparently breaking the upper limit of FOLEDs.