Electrophosphorescent Devices Based on Cationic Complexes: Control of Switch‐on Voltage and Efficiency Through Modification of Charge Injection and Charge Transport
Electrophosphorescent Devices Based on Cationic Complexes: Control of Switch‐on Voltage and Efficiency Through Modification of Charge Injection and Charge Transport
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DOI：
10.1002/adfm.200400218
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发表时间：
2005-02
影响因子：
19
通讯作者：
Edward A. Plummer;A. Dijken;J. W. Hofstraat;L. Cola;K. Brunner
中科院分区：
文献类型：
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作者：
Edward A. Plummer;A. Dijken;J. W. Hofstraat;L. Cola;K. Brunner
本文报道了对掺杂铱配合物的聚合物发光器件（PLEDs）性能的分析。介绍了将带电和中性配合物掺杂到聚（N - 乙烯基咔唑）（PVK）中的器件，并讨论了离子的作用以及配合物的电荷传输特性。在含有带电配合物的器件中，发现配合物的浓度对开启电压和效率都有显著影响。在较高的掺杂浓度下，效率提高，开启电压降低。发现较高掺杂浓度下效率的提高和开启电压的降低是由于通过铱掺杂剂[Ir(bpy)]⁺（六氟磷酸双（2 - 苯基吡啶 - C₂,N′）（2,2′ - 联吡啶）铱）存在一种替代的电荷传输路径。然而，在较低浓度下，该配合物成为电子陷阱，效率降低。发现这些器件的效率明显低于含有中性配合物的器件。这种差异归因于带电配合物的离子含量和电荷俘获特性。通过使用空穴阻挡层可以克服基于带电配合物的器件效率低的问题；获得了效率高达23 cd A⁻¹的器件。
This paper reports an analysis of the properties of polymer light‐emitting devices (PLEDs) doped with iridium complexes. Devices based on charged and neutral complexes doped into poly(vinylcarbazole) (PVK) are presented, and the role of the ions and the charge‐transport properties of the complexes are discussed. In devices with the charged complexes, the concentration of the complex is found to have a profound effect on both the switch‐on voltage and the efficiency. At higher doping concentrations the efficiency is increased and the switch‐on voltage decreased. The increase in efficiency and decrease in switch‐on voltage at higher dopant concentration are found to be due to an alternative charge transport path via the iridium dopant [Ir(bpy)]+ (bis(2‐phenylpyridine‐C2,N′)(2,2′‐bipyridine)iridium hexafluorophosphate). However, at lower concentrations the complex becomes an electron trap and the efficiency is reduced. The devices are found to be significantly less efficient than those with neutral complexes. This difference is attributed to the ionic content and the charge trapping properties of the charged complexes. The low efficiency of the charged‐complex‐based devices could be overcome by utilizing a hole‐blocking layer; devices with efficiencies as high as 23 cd A–1 were obtained.