Novel star-shaped host materials for highly efficient solution-processed phosphorescent organic light-emitting diodes

Article abstract of DOI:10.1039/c0jm00692k

Two novel star-shaped host materials for solution processed blue phosphorescent organic light-emitting devices, 9-(5′,5?-diphenyl[1, 1′:3′,1″:3″,1?:3?,1-quinquephenyl] -5″-diyl)-9H-carbazole (DQC) and 9,9′-(5′-phenyl[1,1′: 3′,1″-terphenyl]-3,5-diyl)bis-9H-carbazole (PTC), were synthesized by the Suzuki coupling reaction. These compounds both exhibited high glass-transition temperatures (T_g ≥ 128 °C) and excellent film-forming ability. The nonplanar star-shaped configuration of DQC and PTC limited the effective extension of their π-conjugation, leading to the same triplet energy of 2.81 eV. The solution processed single layer devices using DQC and PTC as the host for the phosphorescence emitter iridium(iii) bis(4,6-difluorophenylpyridinato)-picolinate (FIrpic) showed the maximum luminance efficiencies of 9.2 and 12.8 cd A^-1, respectively. By introducing a thin 1,3,5-tris(1-phenyl-1H-benzo[d]imidazol-2-yl)benzene (TPBI) electron-transporting and exciton-confining layer, the maximum efficiencies of the solution processed devices based on DQC and PTC were further improved to 21.7 and 25.7 cd A^-1 with the maximum external quantum efficiencies up to 9.2% and 11.9%, respectively. Furthermore, the DQC- and PTC-based devices showed significantly high performance compared with the corresponding devices based on 1,3-bis(9-carbazolyl)benzene (mCP).