Design And Syntheses Of Highly Efficient Blue Host Materials For Phosphorescence And Their Electroluminescent Properties

Organic light-emitting diodes (OLEDs) come out as a new technology at the end of twentieth century and have strong vitality. OLEDs could be applied in the areas like display or lightening. Compared with traditional technologies, OLEDs have a few advantages such as thin, purity of color, wide perspective, fast response, flexible, transparent, large area and colorful. Therefore, OLEDs have wide range of practical applications. So far, the efficiency and life-time of red and green phosphorescent OLEDs (PHOLEDs) have met the practical standard. However, in order to realize the full-color display and white lightening we have to overcome the issues of low efficiency and short life-time in blue PHOLEDs. As the high triplet energy of blue guest materials, the corresponding host, hole and electron transporting materials should possess higher triplet energy, which makes it difficult in the design and syntheses of host materials. In this paper, we designed and synthesized some novel blue host materials which possess high triplet energy and glass-transition temperature. Highly efficient blue PHOLEDs were realized using these host materials. We also did intensive studies on the chemical structures, stabilities, photo-physical properties and electrochemical properties of these host materials. What’s more, density function theory (DFT) was adopted to simulate the chemical structures and the calculated results accords quite well with the experimental results. In this paper, we provide an effective way of designing efficient blue host materials. Detailed information is as follows:1. A novel host material diphenyl(4-(9-phenyl-9H-xanthen-9-yl)phenyl) phosphine oxide (DPPO) was synthesized and characterized. The phosphorescent spectrum shows that this new compound possesses high triplet energy level and can be used as host material for the sky-blue emitter Bis(4,6-difluorophenylpyridine) (picolinate) iridium (Ⅲ) (FIrpic) in phosphorescent OLED. Consequently, the device performance based on DPPO as host material exhibits a current efficiency of 30.6 cd/A, a luminance efficiency of 19.2 lm/W and a maximum external quantum efficiency of 13.6% at the luminance of 100 cd/m2.2. Two novel carbazole derivatives,3,3’-(2,6-dimethyl-1,4-phenylene)bis (9-phenyl-9H-carbazole) (DMCz) and 3,3’-(2,3,5,6-tetramethyl-1,4-phenylene) bis(9-phenyl-9H-carbazole) (TMCz) are designed and synthesized as the host materials for blue phosphorescent organic light emitting diodes (PHOLEDs). Both of the materials possess high enough glass-transition temperatures and triplet energies for the blue dopant Ir-complex Bis(4,6-difluorophenylpyridine)(picolinate) iridium (Ⅲ) (FIrpic,2.65 eV). The device using DMCz as the host material showed a better performance than that of TMCz, with a maximum power efficiency of 36.0 lm/W, a maximum current efficiency of 43.7 cd/A and a maximum external quantum efficiency (EQE)of 17.8%.