Multifunctional metallophosphors with anti-triplet-triplet annihilation properties for solution-processable electroluminescent devices

• Published in: Journal of materials chemistry Vol. 18; no. 15; pp. 1799 - 1809
• Main Authors: ZHOU, Gui-Jiang, WONG, Wai-Yeung, BING YAO, ZHIYUAN XIE, LIXIANG WANG
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 01.01.2008
• Subjects: Applied sciences; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electroluminescence; Electronics; Exact sciences and technology; Materials; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optoelectronic devices; Other luminescence and radiative recombination; Physics; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Fluorene; Frontier orbital; High density; Ligand; Thermogravimetry; Organometallic compound; Strong interaction; Luminescent material; Quantum yield; Thermal properties; Triplet state; Electrochemical properties; Lamellar structure; Electroluminescent device; Organic light emitting diodes; Numerical simulation; Spin-on coating; Photoelectronic properties; Arsenic addition; P type conductivity; Current density; Indium addition; Glassy state
• ISSN: 0959-9428; 1364-5501
• DOI: 10.1039/b718653c

With the goal to provide organometallic triplet emitters with good hole-injection/hole-transporting properties, highly amorphous character for simple solution-processed organic light-emitting diodes, and negligible triplet-triplet (T-T) annihilation, a series of new phosphorescent cyclometalated IrIII and PtII complexes with triphenylamine-anchored fluorenylpyridine dendritic ligands were synthesized and characterized. The photophysical, thermal, electrochemical and electroluminescent properties of these molecules are reported. The incorporation of two sterically hindered electron-rich triphenylamino groups to the 9-position of the fluorene skeleton was found not only to afford triplet emitters in the glassy state with high Tg, but also to elevate the HOMO levels and confer the hole-injection ability to the phosphorescent center. These highly amorphous metal phosphors can serve as doped emitters in a small molecular host for spin-coated emission layer in suitable OLED structures to achieve good device performance with a maximum luminance of 29380 cd m-2 at 23 V, a peak external quantum efficiency of 7.0%, a luminance efficiency of 21.4 cd A-1 and a power efficiency of 2.9 lm W-1. Both the electrophosphorescent device characterization as well as the theoretical simulation results show that these iridium electrophosphors show negligible T-T annihilation even at high operating current densities and moderately high doping levels. Our investigations indicate that attaching the triphenylamino moieties to the fluorene ring is an effective way to overcome the T-T annihilation caused by the strong interactions among the emitting molecules.