New Electron‐Transporting Materials Based on Pyrimidine and Thiazolopyridine Moieties for High‐Efficiency Organic Light‐Emitting Diodes

Using the pyrimidine moiety with electron‐accepting capability and the thiazolopyridine moiety, commonly used as a moiety with an electron‐withdrawing group in organic semiconductors, for the first time 2‐(3‐(4,6‐di(phenanthren‐9‐yl)pyrimidin‐2‐yl)phenyl)thiazolo[5,4‐b]pyridine (DPPTP) is designed and synthesized to enhance electron transport capabilities compared to the conventional electron‐transporting layer, tris(8‐hydroxyquinoline)aluminum (Alq 3 ). The photoluminescence maxima in solution and film states are observed at 391 and 410 nm, respectively. Although the photoluminescence quantum yield is relatively low at 2% in the solution state, it increases to 28% in the film state. The measured electron mobility values from the fabricated device range from 1.46 × 10 −5 to 2.0 × 10 −5 cm 2 V −1 s −1 , ≈5.7 times faster than the electron mobility of Alq 3 . In a fluorescent blue device utilizing the newly synthesized DPPTP as the electron‐transporting layer, the current efficiency is 4.36 cd A −1 , and the external quantum efficiency is 3.76%, representing a 1.3‐fold improvement in efficiency compared to Alq 3 devices.