Carbazole–benzimidazole hybrid bipolar host materials for highly efficient green and blue phosphorescent OLEDs
作者:You-Ming Chen、Wen-Yi Hung、Hong-Wei You、Atul Chaskar、Hao-Chun Ting、Hsiao-Fan Chen、Ken-Tsung Wong、Yi-Hung Liu
DOI:10.1039/c1jm12598b
日期:——
In this study, we synthesized a series of bipolar hosts (CbzCBI, mCPCBI, CbzNBI, and mCPNBI) containing hole-transporting carbazole and electron-transporting benzimidazole moieties and then examined the morphological, thermal, and photophysical properties and carrier mobilities of these bipolar host materials. Altering the linking topology (C- or N-connectivity of the benzimidazole) changed the effective conjugation length and led to different excited-state solvent relaxation behavior. The N-connected compounds (CbzNBI, mCPNBI) possessed higher triplet energies (ET) than those of their C-connected analogues (CbzCBI, mCPCBI) by 0.23 eV. The higher values of ET of CbzNBI and mCPNBI endowed them with the ability to confine triplet excitons on the blue-emitting guest. A blue PhOLED device incorporating mCPNBI achieved a maximum external quantum efficiency, current efficiency, and power efficiency of 16.3%, 35.7 cd Aâ1, and 23.3 lm Wâ1, respectively; confirming the suitability of using N-connected bipolar hosts for the blue phosphor. The donor/acceptor interactions of the C-connected analogue resulted in a lower triplet energy, making it a suitable bipolar host for green phosphors. A green-phosphorescent device incorporating CbzCBI as the host doped with (PBi)2Ir(acac) achieved a maximum external quantum efficiency, current efficiency, and power efficiency of 20.1%, 70.4 cd Aâ1, and 63.2 lm Wâ1, respectively.
在这项研究中,我们合成了一系列含有空穴传输咔唑和电子传输苯并咪唑分子的双极宿主材料(CbzCBI、mCPCBI、CbzNBI 和 mCPNBI),然后考察了这些双极宿主材料的形态、热和光物理性质以及载流子迁移率。改变连接拓扑结构(苯并咪唑的 C 连接或 N 连接)会改变有效共轭长度,并导致不同的激发态溶剂弛豫行为。N 连接化合物(CbzNBI、mCPNBI)的三重能(ET)比其 C 连接类似物(CbzCBI、mCPCBI)高 0.23 eV。CbzNBI 和 mCPNBI 较高的 ET 值赋予了它们将三重激子限制在蓝色发光客体上的能力。采用 mCPNBI 的蓝色 PhOLED 器件的最大外部量子效率、电流效率和功率效率分别达到 16.3%、35.7 cd Aâ1 和 23.3 lm Wâ1 ;这证实了使用 N 连接双极宿主作为蓝色荧光粉的适用性。C 连接类似物的供体/受体相互作用导致了较低的三重能,使其成为绿色荧光粉的合适双极宿主。以 CbzCBI 为宿主,掺杂了 (PBi)2Ir(acac) 的绿色荧光装置的最大外部量子效率、电流效率和功率效率分别达到了 20.1%、70.4 cd Aâ1 和 63.2 lm Wâ1 。