Molecular understanding of diphenylether-, 9,9-biphenylfluorene- and tetraphenylsilane-centered wide bandgap host materials for highly efficient blue phosphorescent OLEDs

Abstract

Organic wide bandgap semiconductor is a hot research topic in optoelectronic fields. In this work, a series of diphenylether-, 9,9-biphenylfluorene- and tetraphenylsilane-centered wide bandgap materials are designed and synthesized. Comprehensive experiments and theoretical calculations are conducted to investigate their intrinsic thermal stability, photophysical property, electrochemical behavior and device performance, aiming at exploring the potentials of oxygen, sp3-hybridized carbon and silicon atoms for wide bandgap materials. They all can interrupt molecular conjugation to generate wide bandgaps. By modification of appropriate donor and acceptor, relatively high triplet energy level (ET) can be obtained in the resulting materials. Quantum chemical calculations indicate the sort of triplet energy levels of N-carbazole > fluorene > benzonitrile, which fully supports the experimental results. Tetraphenylsilane-based materials display lower LUMO levels than corresponding diphenylether- and 9,9-biphenylfluorene-centered materials owing to the dπ-pπ conjugation. Among them, DCzSiPy/FIrpic doped device gives the best device performance with maximum current efficiency of 35.6 cd/A and maximum external quantum efficiency of 16.8%, demonstrating the superiority of tetraphenylsilane skeleton. 9,9-Biphenylfluorene-based doped devices have comparable efficiencies with tetraphenylsilane-hosted ones, meaning 9,9-biphenylfluorene unit also can be a good constructing skeleton for wide bandgap host materials.