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 (Alq₃). 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 cm² V⁻¹ s⁻¹, ≈5.7 times faster than the electron mobility of Alq₃. 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 Alq₃ devices.