1,3,5-Triazine derivatives as new electron transport–type host materials for highly efficient green phosphorescent OLEDs
作者:Hsiao-Fan Chen、Shang-Jung Yang、Zhen-Han Tsai、Wen-Yi Hung、Ting-Chih Wang、Ken-Tsung Wong
DOI:10.1039/b913423a
日期:——
We have synthesized three star-shaped 1,3,5-triazine derivativesâ2,4,6-tris(biphenyl-3-yl)-1,3,5-triazine (T2T), 2,4,6-tris(triphenyl-3-yl)-1,3,5-triazine (T3T), and 2,4,6-tris(9,9â²-spirobifluorene-2-yl)-1,3,5-triazine (TST)âas new electron transport (ET)-type host materials for green phosphorescent organic light-emitting devices. The morphological, thermal, and photophysical properties and the electron mobilities of these ET-type host materials are influenced by the nature of the aryl substituents attached to the triazene core. The metaâmeta linkage between the 1,3,5-triazine core and the peripheral aryl moieties in T2T and T3T limited the effective extension of their Ï conjugation, leading to high triplet energies of 2.80 and 2.69 eV, respectively. Time-of-flight mobility measurements revealed the good electron mobilities for these compounds (each > 10â4 cm2Vâ1 sâ1), following the order T3T > TST > T2T. The device incorporating T2T as the host, doped with (PPy)2Ir(acac) and 1,3,5-tris(N-phenylbenzimidizol-2-yl)benzene (TBPI) as the ET layer, achieved a high external quantum efficiency (ηext) of 17.5% and a power efficiency (ηp) of 59.0 lm Wâ1. For the same device configuration, the T3T-based device provided values of ηext and ηp of 14.4% and 50.6 lm Wâ1, respectively; the TST-based device provided values of 5.1% and 12.3 lm Wâ1, respectively. We ascribe the superior performance of the T2T-based devices to balanced charge recombination; we ascribe the poor efficiencies of the TST-based devices to its relatively low triplet energy (2.54 eV), which did not allow efficient confinement of the triplet excitons on the green phosphorescent emitter (PPy)2Ir(acac).
我们合成了三种星形1,3,5-三嗪衍生物——2,4,6-三(联苯-3-基)-1,3,5-三嗪(T2T)、2,4,6-三(三苯基-3-基)-1,3,5-三嗪(T3T)和2,4,6-三(9,9′-螺二氟烯-2-基)-1,3,5-三嗪(TST),作为绿色磷光有机发光器件的新型电子传输(ET)型主材料。这些ET型主材料的形态、热学和光物理性质以及电子迁移率受到附加在三嗪核心上的芳基取代基性质的影响。T2T和T3T中1,3,5-三嗪核心与外缘芳基的间-间连接限制了其π共轭的有效延伸,导致其 triplet 能量分别达到2.80 eV和2.69 eV。飞行时间迁移率测量显示这些化合物具有良好的电子迁移率(均大于10⁻⁴ cm² V⁻¹ s⁻¹),其顺序为T3T > TST > T2T。以T2T为主材料,与(PPy)₂Ir(acac) 和1,3,5-三(N-苯基苯并咪唑-2-基)苯(TBPI)作为ET层的器件实现了17.5%的高外量子效率(η_ext)和59.0 lm W⁻¹的功率效率(η_p)。在相同的器件配置中,基于T3T的器件的η_ext和η_p分别为14.4%和50.6 lm W⁻¹;而基于TST的器件则分别为5.1%和12.3 lm W⁻¹。我们将T2T基器件的优越性能归因于平衡的电荷复合;而将TST基器件的低效率归因于其相对较低的三重态能量(2.54 eV),这使其无法有效限制三重态激子在绿色磷光发光体(PPy)₂Ir(acac)上。