The Design And Synthesis Of C^N=N Type Iridium Complexes With Yellow/Orange Emission And Their OLEDs/wOLEDs Study

In the background of the global energy shortage, white organic light-emitting diodes(WOLEDs) have drawn much attention because of their excellent properties, such as wide material sources, high efficiency, flexible display and lighting in large area. However, the development process of WOLEDs is hampered by problems such as low device efficiency, color unstability and short lifetime. In order to solve these problems, in this dissertation, by introducing new iridium complexes, two-color WOLEDs with high efficiency and color stability are fabricated. The main contents are listed as follows:Firstly, two new iridium complexes Ir(BPPya)2acac and Ir(BPPya)2pic with C^N=N type ligand were synthesized by introducing 2,4-pentanedione and 2-picolinic acid. Then OLED devices based them ware prepared. The results show that the efficiency of Ir(BPPya)2acac is higher than that of Ir(BPPya)2pic, which is attributed to the higher PLQY of Ir(BPPya)2acac. The maximum efficiencies of Ir(BPPya)2acac and Ir(BPPya)2pic were 49.5 and 34.9 cd/A, respectively.Secondly, a multi-layer WOLED was fabricated using the new synthesized iridium complex Ir(BPPya)2acac and the blue emitter FIrpic [Bis(4,6-difluorophenyl pyridinato-N,C2)picolinatoiridium]. Among three WOLEDs with different structures, the efficiency and color stability of device with emitting structure of blue/orange/blue were the best, which showed maximum current efficiency of 25.3 cd/A. Especially, the CIE coordinates of the WOLED were extremely stable. This can be attributed to bipolar transport of the mixed-hosts(CBP and TPBi), which could effectively transport charges and broaden the exciton recombination zone as well as reduce the accumulation of triplet excitons at the emissive interface.Finally, a single-emissive layer WOLED was fabricated using a new complex Ir(NPPya)3 with strong yellow emission and the blue emitter FIrpic based on complementary strategy. The maximum efficiencies of the WOLED were 55.9 lm/W,49.9 cd/A and 23.9%. To investigate the dominate mechanism for the WOLED with high efficiency, two monochromic devices were constructed by keeping the device structure the same as the WOLED. By the study of energy levels of HOMO and LUMO as well as triplet energy levels of these materials, it can be found that direct charge recombination on the phosphorescent dyes combined with effective triplet energy transfer from the mix-host to the dopants lead to the good performance in this single-emissive layer WOLED.