Fabricate Of High Efficiency Exciplex Based OLEDs And Research Of The Roll-off Character

Organic light-emitting diodes(OLED)have received unprecedented attention from researchers due to its unique advantages in the past half century.After several generations of development of luminous materials,research centers have been shifting from fluorescent materials and phosphorescent materials to thermally assisted delayed fluorescence(TADF)materials and exciplex systems.As another material system which can realize delayed fluorescence emission,exciplex has the advantage of very flexible material selection.However,there are still many gaps in the study of exciplex system,and there are still few high-performance exciplex devices,which limits the development of OLED technology based on exciplex system to a certain extent.In view of the existing gap,this paper studied the advantages of exciplex over the usual host and the influence of molecular conformation on the system of exciplex by exploring the application of exciplex as host and self-illumination.The specific research contents are as follows:(1)Based on the two donor materials Pra-2Me Cz and Prm-2Me Cz,the possibility of exciplex forming with various common acceptors was studied,and a series of devices were designed and fabricated to verify the possibility and superiority as the host.Four high performance OLED devices,including two green devices and two orange-red devices,were fabricated by adjusting the ratio of donor and accepter in the device and adjusting the concentration of phosphorescent guest.Finally,compared with traditional materials host device,in the case of the same color and similar structure,luminous efficiency of exciplex-based is superior to traditional materials host device.Among them,the maximum external quantum efficiency(EQE)of green device reached 20.6%and24.6%,respectively.The maximum external quantum efficiency of orange-red device reached 26.1%and 24.3%,respectively.(2)Two donor materials,Pra-2DMAC and Prm-2DMAC,which have similar chemical structure but completely different molecular conformation,were studied to verify their different roles in exciplex system.Through theoretical calculation,the DMAC fragments in Pra-2DMAC are flat,and the torsion angle between the DMAC fragments and the central aromatic ring is close to 90°,and the whole molecule is vertical.The DMAC fragments of Prm-2DMAC are distorted and the whole molecule is near planar.For vertical molecules,complete separation of HOMO and LUMO orbitals promotes the RISC and the efficiency of exciplex.Pra-2DMAC based device achieves an maximum EQE of 15.0%with a turn-on voltage of 2.4 V and 93%efficiency at 1000 cd·m^-2.The CIE coordinates are almost constant with brightness gross,demonstrate excellent spectral stability.The high performance of Pra-2DMAC proves the superiority of the vertical donor molecule in the exciplex system,this is the first time to study the dual conformation donor material in exciplex based OLEDs.