Hao Yuying

Improved light extraction of organic light emitting diodes with a nanopillar pattering structure

We have investigated the properties of organic light emitting diodes (OLEDs) with a nanopillar patterning structure at organic—metal or organic—organic interfaces. The results demonstrate that the introduction of a nanopillar structure can improve the light extraction efficiency greatly. We also find that the number, height, and position of nanopillars all affect the light extraction of OLEDs. The maximum power efficiency of a device with an optimized nanopillar patterning mode can be improved to 2.47 times that of the reference device. This enhancement in light extraction originates from the improved injected carriers, the broadened charge recombination zone, and the intensified wave guiding effects.

Synthesis and photoelectric performances of blue-green emitting iridium phenylpyridine complexes using N,N′-heteroaromatic ancillary ligands

Four iridium complexes containing different ancillary ligands Htfmpptz = 2-(5-(4-(trifluoromethyl)phenyl)-2H-1,2,4-triazol-3-yl)pyridine, Hfpptz = 2-(5-(4-fluorophenyl)-2H-1,2,4-triazol-3-yl)pyridine and Htfmptz = 2-(5-(trifluoromethyl)-2H-1,2,4-triazol-3-yl)pyridine and ppy (2-phenylpyridine) as main ligands were synthesized and characterized. Their molecular structures were identified by X-ray single crystal diffraction. The effects of ancillary ligands on the photophysical and luminescence behaviors were investigated. The emission maximum peaks of (ppy)2Ir(tfmpptz), (ppy)2Ir(fpptz) and (ppy)2Ir(tfmptz) in CH2Cl2 solution appear at 485, 487 and 483 nm, respectively. Phosphorescent organic light-emitting devices (PhOLEDs) were fabricated using these complexes doped in CBP as an emitting layer.

Electronic Structures and Spectroscopic Properties of a Novel Iridium (III) Complex with an Ancillary Ligand 2-(4-Trifluoromethyl -2-Hydroxylphenyl) Benzothiazole

Iridium (III) complexes with 2-phenylpyridine (ppy) have been demonstrated as a type of promising phosphorescence dopant in emitting layers of organic light emitting diodes (OLEDs). In most iridium (III) complexes, there exist the strong spin-orbit coupling between π-orbitals of cyclometalated ligands and 5d orbitals of the centric iridium. We study a novel iridium (III) complex (ppy)2Ir(4-TfmBTZ) with ppy as cyclometalated ligands and 2-(4-trifluoromethyl-2-hydroxylphenyl)benzothiazole (4-TfmBTZ) as an ancillary ligand using the Gaussian 03 program. The geometries, electronic structures and spectroscopic properties of this iridium (III) complex are investigated by density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The results show that the spin-orbit coupling occurs not only between ppy and iridium atom but also between 4-TfmBTZ and iridium atom in this complex. The highest occupied molecular orbital is dominantly localized on the Ir atom and 4-TfmBTZ ligand, while the lowest unoccupied molecular orbital on 4-TfmBTZ ligand. The triplet lowest-lying transition is attributed to the Ir-to-4-TfmBTZ charge-transfer (3MLCT) transition while the sub-low-lying transitions are assigned to the 3MLCT transitions of Ir(ppy)2. The nature of the lowest unoccupied orbital changes from ppy-localized to 4-TfmBTZ-localized and reveals that phosphorescent color of Ir(III) complex can be controlled by the ancillary ligand and substituent.