Long-Lived and Highly Efficient TADF-PhOLED with "(A)n-D-(A)n" Structured Terpyridine Electron-Transporting Material

The electron-transporting material (ETM) is one of the key factors to determine the efficiency and stability of organic light-emitting diodes (OLEDs). A novel ETM with a "(Acceptor)(n)-Donor-(Acceptor)(n)" ("(A)(n)-D-(A)(n)") structure, 2,7-di([2,2:6,2-terpyridin]-4-yl)-9,9-spirobifluorene (27-TPSF), is synthesized by combining electron-withdrawing terpyridine (TPY) moieties and rigid twisted spirobifluorene, in which the TPY moieties facilitate electron transport and injection while the spirobifluorene moiety ensures high triplet energy (T-1 = 2.5 eV) as well as enhances glass transition temperature (T-g = 195 degrees C) for better stability. By using tris[2-(p-tolyl)pyridine]iridium(III) (Ir(mppy)(3)) as the emitter, the 27-TPSF-based device exhibits a maximum external quantum efficiency (eta(ext, max)) of 24.5%, and a half-life (T-50) of 121, 6804, and 382 636 h at an initial luminance of 10 000, 1000, and 100 cd m(-2), respectively, which are much better than the commercialized ETM of 9,10-bis(6-phenylpyridin-3-yl)anthracene (DPPyA). Furthermore, a higher efficiency, a eta(ext, max) of 28.2% and a maximum power efficiency (eta(PE), (max)) of 129.3 lm W-1, can be achieved by adopting bis(2- phenylpyridine)iridium(III)(2,2,6,6-tetramethylheptane-3,5-diketonate) (Ir(ppy)(2)tmd) as the emitter and 27-TPSF as the ETM. These results indicate that the derivative of TPY to form (A)(n)-D-(A)(n) structure is a promising way to design an ETM with good comprehensive properties for OLEDs.