Design And Synthesis Of Phosphorescent Ir(?) Complexes For Highly Efficient Doping-free/Heavily Doped OLEDs

Recently,organic light-emitting diodes?OLEDs?have drawn extensive attentions owing to their potential applications in flat-panel displays and solid-state lighting.Among numerous luminescent materials for OLEDs,iridium?III?complexes are the most remarkable due to their short exciton lifetimes,good photo-thermal stability,as well as high luminescence quantum yields.In general,phosphorescent emitters have to be blended into suitable host materials to reduce the concentration quenching and/or triplet-triplet annihilation?TTA?effect.However,such design strategies often depend on the doping concentration,require a rather low and narrow concentration range?less than 10%?,resulting in a restriction on their reproducibility of mass production.Additionally,the potential phase separation occurs in blended systems usually leads to poor energy transfer and device degradation over time.Nevertheless,non-doped and/or heavy doping level OLEDs have the benefit of being able to overcome the problems mentioned above.Non-doped architecture is simple,economic and can be easily controlled.The heavy doping-level OLEDs can also make a sophisticated control of the doping process unnecessary which are greatly beneficial for improving the product yield of commercial mass production in the future.Therefore,it is important to design and synthesize efficient iridium?III?complexes for high performance non-doped and/or heavy doping level OLEDs.In this paper,we designed and synthesized a series of novel iridium?III?complexes possessing different cyclometalated or ancillary ligands by molecular engineering.These complexes-based devices have been successfully fabricated through investigating their photophyical,electrochemical and thermal properties.The relative studies are outlined as follows:?1?The design and synthesis of green iridium?III?complexes modified with fluorine atoms pyridine-1,2,4-triazolyl ligands and their photophyical,electrochemical and thermal properties have been investigated in detail.Both the heavy doping-level?20%?and non-doped devices employing these complexes as emitting layers have been successfully fabricated.The results suggested that rational incorporation of fluorine atoms into the ancillary ligands could significantly improve the performance of device with features of high efficiency and small roll-off.?2?Synthesis of highly efficient yellow-green iridium?III?complexes and fabrication of excellent non-doped devices.Here,carbazole and diphenylphosphoryl groups,were incorporated into different position of 1,2-diphenyl-H-benzimidazole?HPBI?ligands.These functional units used as steric hindrance and manipulated the charge transporting abilities simultaneously.As a result,all of the iridium?III?complexes-based non-doped devices exhibited the state-of-the-art performance,with a maximum current efficiency of 29.7 cd A^–1and power efficiency of 31.1 lm W^–1,which were almost 3-fold than that of the control device(11.1 cd A^–1,11.6 lm W^–1).Inspiringly,they showed obviously reduced efficiency roll-off as luminance increases.?3?Synthesis of highly efficient orange-red iridium?III?complexes and fabrication of three-color doping-free hybrid WOLEDs.Their crystal packing diagrams and charge transporting ability were investigated in detail.Firstly,doping-free monochromatic devices were fabricated and obtained considerable efficiencies.Further optimizing device structure,three-color doping-free hybrid WOLEDs have been successfully fabricated as well.WOLED exhibited low turn-on voltages of 2.5 V,low driving voltages of 3.3 V at 100 cd m^-2 and 4.2 V at 1000 cd m^-2,high luminance of 34505 cd m^-2,high efficiencies(24.2 cd A^-1,21.7 lm W^-1,and 10.3%).In addition,WOLED exhibited warm white emission with correlated color temperature?CCT?and Commission Internationale de L'Eclairage?CIE?coordinate of 2948K and?0.44,0.41?.