Efficient donor-acceptor host materials for green organic light-emitting devices: non-doped blue-emissive materials
Jayaraman Jayabharathi1, Palanisamy Sujatha1, Venugopal Thanikachalam1
1Department of Chemistry, Annamalai University Annamalainagar 608 002 Tamilnadu India jtchalam2005@yahoo.co.in +91 9443940735.
Abstract:
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.
