Adjusting Nitrogen Atom Orientations of Pyridine Ring in Tetraphenylsilane-Based Hosts for Highly Efficient Blue Phosphorescent Organic Light-Emitting Devices

摘要

Four wide bandgap 'host materials, namely, 9-(4-diphenyl(4(pyridin-s-yl)phenypsilyl-phenyl)-9H-carbazole (CSmP), 9-(4-diphenyl)-4(pyridin-2-yl)phenyl)silylpheny-O-9H-carbazole (cSoP), 9-(4-dipheny1(4-(pyrphe nyl) silylp h enyl)-9H-3,91=b icarb az ol e (D CSmP),-and 9- (4(dipheny1(44pyridin-2-yOphenyl)sily0phenyl)-9H-3,9'-bicarbazole (DCSo-P), have developed by incorporation of pyridine with varied-N atom orientation and, carbazole/dimer:carbazole units, into the tetraphenylsilane skeleton for blue phosphorescent-light-emitting diodes. These host materials all possess wide bandgap (3.543.64 eV), and high triplet energies (2,77-2.95 eV). As revealed by the absorption and emission spectra, theoretiCal,calculations, and CV measurements, the N atom orientation exerts a strong influence on the LUMO energy level and electron-transportation behaviors-without deterioring the photophysical properties. Among them, DcSmP with 3-pyridyi substituent manifests the best,electron-transporting capability. The- FIrpic-doped blue phosphorescent device using DCSmP as host material exhibits excellent electroluminescence performance with a maxim-urn current efficiency of 40.1 cd A-1. and a maximum external quantum efficiency of 20.0%.. The current efficiency and external quantum efficiency are improved 3-fold,-higher than those fabricated from DeSpP with 4-pyridyl as substituent,-demonstrating an effective strategy for large improvement in device performance by a subtle change in molecular structure.