Long‐Lived and Highly Efficient TADF‐PhOLED with “(A)_n–D–(A)_n” Structured Terpyridine Electron‐Transporting Material

Abstract 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 (T₁ = 2.5 eV) as well as enhances glass transition temperature (T_g = 195 °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 (η_{ext, max}) of 24.5%, and a half‐life (T₅₀) 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 η_{ext, max} of 28.2% and a maximum power efficiency (η_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)₂tmd) 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.