High-Efficiency Organic Electrophosphorescent Diodes Using 1,3,5Triazine Electron Transport Materials

This paper reports on novel electron transport materials, 1,3,5-triazine derivatives (TRZ), which have been useful in highefficiency electrophosphorescent (EP) organic light-emitting diodes (OLEDs). We synthesized four 2,4,6-tris(diarylamino)1,3,5-triazine derivatives (TRZ1-TRZ4) that had electron-donating substituents and examined their OLED characteristics. Of these, we found that TRZ 2, 3, and 4 function as a host for tris(2-phenylpyridine)iridium (Ir(ppy)3) and, in particular, 2,4,6tris(carbazolo)-1,3,5-triazine (TRZ2) demonstrated a very high external electroluminescent (EL) quantum efficiency ((eta)ext) of ~10.2 ± 1.0% and an energy conversion efficiency ((eta)energy) of 14.0 ± 2.0 lm/W. Detailed transient photoluminescent (PL) measurement revealed that the triplet energy level of TRZ2 (ET1 = 2.81 eV) is higher than that of conventional 4,4ʹN,Nʹ-dicarbazol-biphenyl (CBP) (ET1 = 2.56 eV), suggesting that TRZ2 has excellent capabilities in confining Ir(ppy)3 triplet excitons.