Highly Efficient Organic Light-emitting Diodes Based On Double Reverse Intersystem Crossing System

Organic light-emitting diodes(OLEDs)with the exceptional characteristic of high device efficiency,superior color quality,thinness,wide viewing Angle and unique self-emission have drawn tremendous attention as solid-state lighting sources.In order to improve the applications,great endeavors have been made to achieve high efficiency OLEDs,such as device structure and materials.However,high efficiency OLEDs phosphorescent OLEDs adopt host-guest doping technology,which complicates the manufacturing process and increase the commercialization cost.The ultrathin emission layer(UEML)technology provides a great potential for researchers to simplify OLEDs structure.However,due to narrow exciton recombination regions,the devices based on UEML always suffer from significant excitons quenching.To loosen the bottleneck,we combine interfacial exciplex with thermally activated delayed fluorescence(TADF)sensitization technology to fabricate orange OLED based on ultrathin emission layer(UEML),and obtain white OLED by constrain energy transfer among emission layers.The interfacial exciplex is used as host for devices,which is constructed by electron donor 2,6-bis(3-(carbazol-9-yl)phenyl)pyridine(26DCzPPy)and electron acceptor of(1,3,5-triazine-2,4,6-triyl)tris(benzene-3,1diyl)tris(diphenylphosphineoxi-de)(PO-T2T).Then we fabricate UEML-based OLEDs with low turn-on voltages 2.4 V,which obtains the maximum forward-view current efficiency(CE)and power efficiency(PE)of 43.0 cd/A,54.1 lm/W.For improving the performance of devices,the TADF of(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-10H-spiro[acr-idine-9,9'-fluorene](Spiro AC-TRZ)is used to sensitize devices.The optimized device achieves maximum CE,PE of 59.0 cd/A,74.1 lm/W and the CE increases by 37.2%compared with the previous devices.And the maximum EQE is 20.4%which remains 18.7%at 1000 cd/m~2.In addition,we explore the reason of improvement of device by theoretical method and experiment.It turned out that the exciton quenching was relieves by double reverse intersystem crossing system(RICS)form exciplex and TADF,which improved the exciton utilization and device performance.Based on the above-mentioned optimized orange OLEDs,we further design stable spectra and high-efficiency WOLEDs.First,we increase the thickness of the sensitizer layer to enhance blue component in devices.The device with 15 nm blue-emission-layer achieves superior performance,showing maximum efficiency of 61.1 lm/W.However,the blue emission is much weaker due to efficient energy transfer between orange UEML and sensitizer layer.In order to increase blue light intensity,the 26DCzPPy interlayer is introduced at the interface between orange UEML and blue emission layer.The high performance WOLED device with 3 nm26DCzPPy interlayer achieved maximum CE,PE of 52.4 cd/A,60.9 lm/W.The stable spectra were obtained and slight CIE coordinates shift from 207cd/m~2 to 17450 cd/m~2 with?CIE only(0.002,0.016).The excellent device performance is ascribed to double RICS,which enhance F(?)rster energy transfer and constrain excitons to form directly on EMLs.