Highly Efficient Fluorescent Organic Electroluminescent Diodes Based On Doping-free Phosphorescent Sensitization System

Organic Lighting-Emitting Diode(OLED)has a broad application prospect in the field of solid lighting and flat display.Compared with traditional devices,OLED has excellent features,such as less power consumption,high efficiency,and flexibility.In the past few decades,researchers have continuously developed new materials and optimized the structure of the device,so the performance of OLED has been significantly improved.Though traditional fluorescent OLED has long life and low roll-off,their internal quantum efficiency is only 25% theoretically.It is an effective way to improve the efficiency of fluorescent OLED by phosphorescent sensitization technology,which needs the low doping concentrations of phosphor sensitizers in the emission layer.However,the co-evaporation of various materials greatly increases the manufacturing complexity of fluorescent OLEDs.In this paper,efficient orange and white fluorescent OLEDs with simple device structure are successfully realized by combining doping-free phosphorescent sensitization system with thermally activated delayed fluorescence material,which the host material is the 9,9-dimethyl-9,10-dihydroacridine-diphenylsulph,and 2,8-di(tbutyl)-5,11-di[4(tbutyl)phenyl]-6,12-diphenylnaphthacene(tetra(t-butyl)rubrene as the dopant.First of all,we optimize concentration of guest in the host material and evaluate the main exciton recombination zone precisely.Then different ultrathin sensitization layers are inserted into the main exciton recombination,which realize orange device with the maximum efficiency of 26.0 cd/A(23.3 lm/W).We further increase the magnitude of ultrathin sensitization layers to improve the efficiency of devices,one of which shows the maximum efficiency of 41.8 cd/A(37.5 lm/W)and the external quantum efficiency reaches 14.1%.By systematically investigating the energy transfer process of host,guest and sensitizer materials,we believe that the introduction of doping-free phosphorescent sensitization system and the use of thermally activated delayed fluorescence material promote the F(?)rster energy transfer process between host and guest.So the triplet excitons become more efficient to achieve higher efficiency.Finally,warm white light devices with high color stability are achieved by manipulating the doping concentration of the guest,and the maximum power efficiency is up to 38.5 lm/W.This result remarkably simplifies manufacturing difficulty of high performance fluorescent OLEDs,which offers a feasible way to commercial mass production.