Abstract
In this thesis, a series of emitters and host materials for deep red PhOLEDs have been synthesized and characterized. These new iridium complexes with obviously MLCT characters are composed of 2-(thiophen-2-yl)quinoline derivatives as ligands, showing the emission maximums at 596‒678 nm with relatively narrow FWHM of 37‒56 nm. The added functional groups, especially to the 4-position of quinoline of the complexes, provided effectively steric interactions for easing the self-quenching, thus high quantum yields of 0.08‒0.38 can be achieved. The best result shows that the device using (mtpq)2Ir(acac) as the dopant reached EQEmax of 21.6% and PEmax of 10.9 lm W-1 with pure red CIE coordinate of (0.70, 0.30). The electroluminescent devices utilizing (mtmq)2Ir(tmd) and (mtpq)3Ir as dopants also reached great consequences of EQEmax of 19.0% and 20.4% and PEmax of 10.9 lm W-1 and 18.2 lm W-1 with CIE coordinate of (0.68, 0.32) and (0.66, 0.34), respectively. However, the unstable status of the Ir complexes like emitters in the excited state or emitter radicals generated from the carrier trapping process would decline the brightness of the devices, resulting in a short operating lifetime (T50). In the studied of the bipolar hosts, we introduced quinoxaline and cabazole moieties into one single molecule, providing the electron accepting and donating parts of the host materials for reducing the energy barrier of carrier injections. The fluorescent and phosphorescent emission spectra of them were measured in thin-film, and the maxima appeared at 443‒520 nm and 533‒569 nm, respectively, which overlap very well with the MLCT absorption bands of deep-red iridium complexes, providing highly effective routes for the energy transfer from the host to the dopant. Consequently, the device using pCzDMQ as the host, (mtpq)2Ir(acac) and (mtpq)3Ir as the dopants have been demonstrated a better EQEmax of 23.9% and 23.5%, and PEmax of 12.7 lm W-1 and 26.5 lm W-1, respectively. In addition, all the host materials performed highly thermal stabilities with Tg of 114‒165 °C and Td of 380‒449 °C, so that the device with long-term stability can be reached by using mCzDPQ/Ir(piq)3 as emitting layer, showing EQEmax of 16.0%, PEmax of 15.9 lm W-1 and T50 of 13939 h at the initial brightness of 500 nits.