Simple bipolar host materials incorporating CN group for highly efficient blue electrophosphorescence with slow efficiency roll-off
作者:Lijun Deng、Jiuyan Li、Ge-Xia Wang、Li-Zhu Wu
DOI:10.1039/c3tc31893a
日期:——
A group of small-molecular compounds, namely 6-(3-(9H-carbazol-9-yl)phenyl)-9-ethyl-9H-carbazole-3-carbonitrile (m-CzCzCN), 6-(2-(9H-carbazol-9-yl)phenyl)-9-ethyl-9H-carbazole-3-carbonitrile (o-CzCzCN), 6-(3,5-di(9H-carbazol-9-yl)phenyl)-9-ethyl-9H-carbazole-3-carbonitrile (mCPCzCN), 8-(3-(9H-carbazol-9-yl)phenyl)dibenzo[b,d]furan-2-carbonitrile (m-CzOCN), 8-(3-(9H-carbazol-9-yl)phenyl)dibenzo[b,d]thiophene-2-carbonitrile (m-CzSCN), are designed and synthesized for use as host materials in blue phosphorescent organic light-emitting diodes (PhOLEDs). The p-type carbazole and the n-type cyano-decorated carbazole, dibenzofuran or dibenzothiophene unit are incorporated, to either the meta- or ortho-positions of the phenylene bridge. The bipolar feature was confirmed by theoretical calculation and experimental results of the single-carrier devices. These materials exhibit an excellent performance in their hosted blue phosphorescent OLEDs with iridium(III)bis(4,6-(difluorophenyl)pyridinato-N,C2′)picolinate (Firpic) as the doped emitter. The ortho-substituted o-CzCzCN realizes higher device efficiencies than the meta-substituted isomer m-CzCzCN, with a maximum external quantum efficiency of 21.0% and a current efficiency of 43.9 cd A−1. The device hosted by m-CzSCN also exhibits remarkably high efficiencies of 23.3% and 46.1 cd A−1. Furthermore, these blue PhOLEDs are characterized by a slow efficiency roll-off. Even at a high brightness of 10 000 cd m−2, the o-CzCzCN hosted device still retain high efficiencies of 13.6% and 28.5 cd A−1. This is a systematic study of incorporating the CN group onto carbazole, dibenzofuran and dibenzothiophene, to develop high-triplet-energy bipolar hosts for OLED applications.
这项研究设计和合成了一组小分子化合物,用作蓝光磷光有机发光二极管(PhOLEDs)的主体材料。这些化合物包括:
1. m-CzCzCN (6-(3-(9H-咔唑-9-基)苯基)-9-乙基-9H-咔唑-3-腈)
2. o-CzCzCN (6-(2-(9H-咔唑-9-基)苯基)-9-乙基-9H-咔唑-3-腈)
3. mCPCzCN (6-(3,5-二(9H-咔唑-9-基)苯基)-9-乙基-9H-咔唑-3-腈)
4. m-CzOCN (8-(3-(9H-咔唑-9-基)苯基)二苯并[b,d]呋喃-2-腈)
5. m-CzSCN (8-(3-(9H-咔唑-9-基)苯基)二苯并[b,d]噻吩-2-腈)
主要研究发现:
- 这些材料将p型咔唑和n型氰基修饰的咔唑、二苯并呋喃或二苯并噻吩单元结合到苯撑桥的间位或邻位
- 单载流子器件的理论计算和实验结果证实了其双极性特征
- 使用FIrpic作为掺杂发光体时,这些材料在蓝光磷光OLED中表现出优异性能
- 邻位取代的o-CzCzCN比间位取代的m-CzCzCN具有更高的器件效率,最大外量子效率达21.0%,电流效率达43.9 cd A−1
- m-CzSCN主体的器件也展现出显著高效率:23.3%和46.1 cd A−1
- 这些蓝光PhOLEDs的效率衰减缓慢,在高亮度(10,000 cd m−2)下,o-CzCzCN主体器件仍保持13.6%和28.5 cd A−1的高效率
这是一项将CN基团引入咔唑、二苯并呋喃和二苯并噻吩以开发高三重态能量双极性主体材料用于OLED应用的系统研究。