Efficient donor–acceptor host materials for green organic light-emitting devices: non-doped blue-emissive materials with dual charge transport properties

Comparative optical, electroluminescence and theoretical studies were performed for (E)-4′-(1-(4-(2-(1-(4-morpholinophenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)vinyl)phenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-diphenyl-[1,1′-biphenyl]-4-amine (SMPI-TPA) and (E)-4-(4-(2-(4-(2-(4-(9H-carbazol-9-yl)phenyl)-1H-phenanthro[9,10-d]imidazol-1-yl)styryl)-1H-phenanthro[9,10-d]imidazol-1-yl)phenyl)morpholine (SMPI-Cz). These compounds show excellent thermal properties, dual charge transport properties and form thin films under thermal evaporation. Blue OLEDs (CIE: 0.16, 0.08) based on SMPI-TPA show efficient device performance (η(ex) 6.1%; η(c) 5.3 cd A(−1); η(p) 5.2 lm W(−1)) at low turn-on voltages. Both SMPI-TPA and SMPI-Cz were utilised as hosts for green OLEDs. The devices with SMPI-Cz (30 nm):5 wt% Ir(ppy)(3) exhibit maximum luminance of 20 725 cd m(−2), and η(c) and η(p) values of 61.4 cd A(−1) and 63.8 lm W(−1), respectively. In comparison, devices with SMPI-TPA (30 nm):5 wt% Ir(ppy)(3) exhibit high η(c) and η(p) values of 65.2 cd A(−1) and 67.1 lm W(−1), respectively. Maximum η(ex) values of 19.6% and 23.4% were obtained from SMPI-TPA:Ir(ppy)(3) and SMPI-Cz:Ir(ppy)(3), respectively. These device performances indicate that the phenanthroimidazole unit is a tunable building unit for efficient carrier injection and it may also be employed as a host for green OLEDs.