Construction Of Organic Deep-blue Electroluminescent Materials And Devices Based On Triazole Element

The materials and devices of Organic Light-Emitting Diodes?OLEDs?have made great progress in the past few years.The development of deep blue luminanscence materials can not only expanding the color gamut,but also effectively reduce the power consumption in full-color OLED displays.However,there are many difficulties in achieving deep blue emission,such as unbalanced carrier injection and transmission,and difficulty in obtaining deep blue light and high device efficiency at the same time,etc.,which still restrict the development of organic deep blue fluorescent materials.In order to perfect the design strategy of deep blue fluorescence materials and explore their properties in OLED devices,the following studies have been made.First,D-?-A fluorescent molecule PCZTZ was synthesized using9-phenylcarbazole as the donor and 2,3,4-triphenyl-1,2,4-triazole as the acceptor.PCZTZ exhibits a distorted molecular structure and exhibits deep-blue emission in the solid state.Due to the strong CH-N interactions in the molecules,a three-dimensional supramolecular H-bond network is formed between the molecules,showing a efficient and balanced carrier mobility.The hole and electron mobilities measured by time-of-flight method are as high as 10^-44 cm² V^-11 s^-1.The maximum external quantum efficiency of the undoped OLED device with PCZTZ as the emission layer is 6.57%,the peak of the electroluminescence spectrum is at 408nm,the CIE coordinates are?0.17,0.07?,the exciton utilization rate is 65.7%.The high exciton utilization rate comes from the hybrid local charge transfer?HLCT?state in the molecule.In addition,due to its excellent carrier transport capability and suitable triplet energy level,the phosphorescent devices with PCZTZ as host materials also show high efficiency,the maximum external quantum efficiency of green and red phosphorescent doped devices are 20.08%And 19.34%,and show stable color stability.In order to further adjust the emission,a push/pull electron group was introduced on the acceptor group to change the strength of the acceptor,and PCZTZT and PCZTZCN were designed and synthesized.By studying their photophysical properties and electroluminescence properties,to adjusted the design strategy of deep blue light molecules.The excited states of both compounds show the characteristics of the HLCT state.The non-doped devices with PCZTZT and PCZTZCN as the light-emitting layer both achieve efficient deep blue light emission.The maximum external quantum efficiency of the device with PCZTZT as the light-emitting layer is2.31%,and the CIE coordinate is?0.16,0.04?.The maximum external quantum efficiency of the device with PCZTZCN as the light-emitting layer is 3.01%,and the CIE coordinate is?0.16,0.05?.The CIEy values of both of them are significantly reduced compare with PCZTZ.It shows that the molecular design strategy using triazole as the acceptor can effectively achieve deep-blue electroluminescence,and the fine-tuning of the acceptor group can effectively adjust the color of the molecule in electroluminescence.group can effectively adjust the light color of the molecule in electroluminescence.