Design And Optimization Of Organic Light-emitting Diodes Based On Iridium Complexes

Organic light-emitting diodes(OLEDs)have attracted great interest throughout the world owing to their potential applications in full-color flat panel displays and solid-state lighting.According to the difference of the luminescent mechanism and processes,organic electroluminescent materials can be divided into phosphorescence materials and fluorescence materials.Phosphorescent materials have been extensively studied as the electroluminescent materials bacauseboth singlet and triplet excitons can be harvestedand thus 100% internal quantum efficiency was expected.In this work,we focused on the design of device structure and the optimization of fabrication technologies of OLEDs.A series of single light-emitting layer(SEML)and double light-emitting layer(DEML)OLEDs with high efficiency were designed and fabricated by selecting blue phosphorescent Ir complex FCNIrpic and red phosphorescent Ir complex Ir(piq)3 as emitter,respectively.Firstly,by utilizing the blue phosphorescent Ir complex FCNIrpic and the bipolar material CzSi as emitter and host,respectively,we have designed and obtained the blue phosphorescent EML devices with high efficiency.To optimize the device structure,we added TcTa as theladder layer between hole transfer layer(HTL)and EML.Compared with the previous reported devices based on FCNIrpic with different device structures,we have also researched the transfer and distribution of carriers within these devices with the help of device performances and EL spectra.Experimental results displayed that adding the ladder layer between HTL and EML could improve the injection and transfer of holes,thus improving the efficiency as well as the color purity.Then,red phosphorescent devices were also designed and fabricated by utilizing the high efficiency red phosphorescent Ir complex Ir(piq)3,TcTa and 26 DCz PPy as emitter,hole type host material and bipolar host material,respectively.To further optimize the device structure,another Ir complex FIrpic,which possessed the low HOMO/LUMO energy level,was selected and co-doped into EML to sensitize the red phosphorescent Ir complex Ir(piq)3.Experimental resultsdemonstratedthat co-doping sensitizer material FIrpic into EML helps to improve the device performances and to slow the efficiency roll-off.By analyzing the distribution of carriers within EML,we have researched the effect of FIrpic molecules on the EL processes of sensitized red phosphorescent devices in detail.In addition,the mechanisms of improved device performances and slowed efficiency roll-off of thesesensitized devices wereanalyzed.Finally,we found the sensitizer material FIrpic function as deeper electron trappers within EML,which broadens the recombination zone and balance the distribution of carriers,thus improving the device performances and slowing the efficiency roll-off.