Synthesis Of New Bipolar Hosts For Blue Phosphor And Their OLED Device Study

Organic light-emitting diodes(OLEDs) have been considered to be a very active research area in the field of the organic semiconductor industry. In particular, phosphorescence OLEDs(Ph OLEDs) are famous for their ability of 100% internal quantum efficiency(IQE), while that of typical fluorescence OLEDs is generally limitated to 25%. Thus, Ph OLEDs are intensively studied these years, including the hosts for phosphors. In terms of hosts, bipolar transport is desired due to its ability to balance charge carrier in the emissive layer. This article focuses on the synthesis of bipolar hosts for blue phosphor and study on their OLED devices. The main contents are listed as follows:Firstly, a new host material based on phosphine oxide/fluorene hybrid for blue phosphor were designed and synthesized. The photophysical properties, electrochemical properties, thermal properties and the device performance were further studied. Blue phosphorescent OLEDs hosted by TPFTPO(Tri(4-(9-9-phenyl-9H-fluoren))phenylphospine oxide) show the maximum current efficiency of 17.7 cd/A through the optimization of device structure.Secondly, two structurally similar pure hydrocarbon molecules of m TPFB(1,3,5-tris(9-phenyl-9H-fluoren-9-yl)benzene) and t Bu-m TPFB(1,3,5-tris(2-tert-butyl-9-phenyl-9H-fluoren-9-yl)benzene) were synthesized, which are expected to be good candidates as hosts for blue Ph OLED. By the study on their thermal, electrochemical, electronic absorption and photoluminescent properties, it was found that the influence of the inert tert-butyl group to material photoelectrical properties are negligible. However, the encapsulation of tert-butyl on the 2-position of 9-phenylfluorene enhanced material thermal stability. Most importantly, carrier transport properties improved dramatically despite the ambipolar transport properties of the both compounds, as proved by the mono carrier device.Finally, blue phosphorescent OLEDs hosted by t Bu-m TPFB show external quantum efficiency of 15.2% and current efficiency of 23.0 cd/A, which is much higher than the OLEDs based on m TPFB with the analogous structure.