The role of exciplex states in phosphorescent OLEDs with poly(vinylcarbazole) (PVK) host
The role of exciplex states in phosphorescent OLEDs with poly(vinylcarbazole) (PVK) host
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DOI：
10.1016/j.orgel.2015.02.002
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发表时间：
2015-05
影响因子：
3.2
通讯作者：
V. Jankus;K. Abdullah;Gareth C. Griffiths;H. Al-Attar;Yonghao Zheng;M. Bryce;A. Monkman
中科院分区：
文献类型：
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作者：
V. Jankus;K. Abdullah;Gareth C. Griffiths;H. Al-Attar;Yonghao Zheng;M. Bryce;A. Monkman
聚合物发光二极管 (PLED) 可能会彻底改变照明和显示行业。 PLED 可以在大面积基板上印刷显示器或照明面板，从而避免 OLED 技术目前使用的昂贵真空工艺，从而大幅降低制造成本。 PVK 是最受欢迎的蓝色 PLED 主机之一。然而，PVK 的电子传输性能非常差，并且基于恶二唑的电子掺杂剂，例如PBD 或 OXD-7 用于改善电荷传输。这通常归因于 PBD 或 OXD-7 上电子的捕获和传输。在这里，我们表明这不一定是 PVK 掺杂效率提高的唯一原因。我们证明，PVK 掺杂有 PBD 或 OXD-7 的器件的发射持续时间长达 1 毫秒，在某些情况下可能比最初在掺杂剂上形成的激子的瞬时发射更长。这种长寿命发射主要是由于 PVK 和 PBD/OXD-7 之间形成激基复合物而产生的。然后，这种激基复合物状态会在很长一段时间内重新填充掺杂剂铱络合物，从而产生非常长寿命的发射。我们还注意到，在几种掺杂有蓝色或绿色铱磷光体的 PBD 和 PVK（以及 OXD-7）的 PLED 中观察到了重金属配合物的这种由激基复合物供给的长寿命发射，表明这是一种普遍现象。
Polymer light emitting diodes (PLEDs) may revolutionize lighting and display industries. PLEDs would enable printing of display or lighting panels on large area substrates that could substantially reduce fabrication costs by avoiding expensive vacuum processes presently used in OLED technologies. PVK is one of the most popular hosts for blue PLEDs. However, PVK has very poor electron transport properties and oxadiazole based electron dopants, e.g. PBD or OXD-7, are used to improve charge transport. This is generally ascribed to capture and transport of electrons on the PBD or OXD-7. Here we show that this is not necessarily the only reason for improved efficiency upon PVK doping. We demonstrate that devices with PVK doped with PBD or OXD-7 have emission lasting up to 1 ms which in some cases may be greater than prompt emission from excitons formed initially on the dopant. This long-lived emission is arising mainly due to formation of an exciplex between the PVK and PBD/OXD-7. This exciplex state then repopulates dopant iridium complexes over a long period of time giving very long-lived emission. We also note that this exciplex-fed long-lived emission from heavy metal complexes is observed in several PLEDs with PBD and PVK (and also OXD-7) doped with blue or green iridium phosphors indicating this to be a general phenomenon.