Design Synthesis And Optoelectronic Of Bipolar Wide Bandgap Host Material Based On Tetraphenylsilane

Host materials have significant influence on the preparation of efficiency in the second generation heavy metal complex phosphorescent materials. Since phosphorescent dyes generally have fairly long excited-state life times which leads to a serious triplet-triplet annihilation. The main function of host materials is dispersing the guest materials to restrain this problem.Most traditional host materials are Unipolar materials and their narrowingof exciton recombination region result of badly TTA leads to efficient roll-off. Besides, it may engender excimer to make peak of spectrum shift. Whereas Bipolar host materials can relieve this problem through broaden exciton recombination region, since bipolar materials contain both hole and electron transporting group.However, the spectrum peak red-shift may be caused by intramolecular charge transfer between donor and acceptor, so it is not easy to buildbrilliant wide bandgap bipolar host materials.We noticed that Si in tetraphenylsilane adopt sp3 hybridization, and the geometry configuration of tetraphenylsilane is regular tetrahedron. It means that tetraphenylsilane has the ability of interrupting the conjugation between the donor and acceptor. Then by connecting both hole and electron transporting group through a tetraphenylsilane, designed and synthesized a series of wide bandgap host materials that have ability of balancing hole and electron transporting and injection. Enriching materials systems and serving as a guide for designing host materials in the future.Through summarizing a number of literature and previous works, We select carbazole and di-carbazole as hole transporting group, and pyridine and diphenylphosphrine oxide as electron transporting group, tetraphenylsilane as core, and a series carriers balance host materials were designed and synthesized.In Chapter 2, we focus on designing wide bandgap polymer materials, which can fabricate the low-cost soltion processing devices due to their good solubility and morphology. By tetraphenylsilane and fluorene backbone and attaching carbazole and diphenylphosphrine oxide on the side chain, PFSCPO shows good thermal stability, morphology and high molecular weight. It’s emission peaks of films are about 430 nm and Ir(ppy)3-doped phosphorescent devices exhibit excellent EL performancewith a maximum current efficiency of 4.2% and the turn on voltage are lower than the devices whose host material does not have diphenylphosphrine oxide group.In the next Chapter, Four wide bandgap host materials have been developed by incorporating pyridine with various N atom orientations and carbazole/dimer carbazole units into tetraphenylsilane skeleton for blue phosphorescent light emitting diodes. As revealed by the absorption and emission spectra and CV measurements, the difference of N atom positions shows strong influence on the LUMO energy levels and electron-transport behaviors without deterioring the photophysical properties. Among them, DCSm P with 3-pyridyl substituent manifested the best electron transport properties. FIrpic-doped blue phosphorescent device using DCSm P as the host exhibits excellent EL performance with a maximum current efficiency of 40.1 cd A-1 and a maximum external quantum efficiency of 20.0% and has weak efficient roll off.