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首页> 外文期刊>Advanced Functional Materials >Highly Efficient, Solution-Processed, Single-Layer,Electrophosphorescent Diodes and the Effect of Molecular Dipole Moment
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Highly Efficient, Solution-Processed, Single-Layer,Electrophosphorescent Diodes and the Effect of Molecular Dipole Moment

机译：高效，固溶处理的单层电致磷光二极管和分子偶极矩的影响

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摘要

A new family of highly soluble electrophosphorescent dopants based on a series of tris-cyclometalated iridium(Ⅲ) complexes (7-4) of 2-(carbazol-3-yl)-4/5-R-pyridine ligands with varying molecular dipole strengths have been synthesized. Highly efficient, solution-processed, single-layer, electrophosphorescent diodes utilizing these complexes have been prepared and characterized. The high triplet energy poly(9-vinylcarbazole) PVK is used as a host polymer doped with 2-(4-biphenylyl)-5-(4-tert-butyl-phenyl)-1,3,4-oxadiazole (PBD) for electron transport. Devices with a current efficiency of 40 cd A1 corresponding to an EQE of 12% can thus be achieved. The effect of the type and position of the substituent (electron-withdrawing group (CF_3) and electron-donating group (OMe)) on the molecular dipole moment of the complexes has been investigated. A correlation between the absorption strength of the singlet metal-to-ligand charge-transfer (~1MLCT) transition and the luminance spectral red shift as a function of solvent polarity is observed. The strength of the transition dipole moments for complexes 1-4 has also been obtained from TD-DFT computations, and is found to be consistent with the observed molecular dipole moments of these complexes. The relatively long lifetime of the excitons of the phosphorescence (microseconds) compared to the charge-carrier scattering time (less than nanoseconds), allows the transition dipole moment to be considered as a "quasi permanent dipole". Therefore, the carrier mobility is sufficiently affected by the long-lived transition dipole moments of the phosphorescent molecules, which are randomly oriented in the medium. The dopant dipoles cause positional and energetic disorder because of the locally modified polarization energy. Furthermore, the electron-withdrawing group CF_3 induces strong carrier dispersion that enhances the electron mobility. Therefore, the strong transition dipole moment in complexes 3 and 4 perturbs both electron and hole mobilities, yielding a reduction in exciton formation and an increase in the device dark current, thereby decreasing the device efficiency.
机译：基于一系列具有不同分子偶极强度的2-（咔唑-3-基）-4 / 5-R-吡啶配体的三环金属化铱（Ⅲ）配合物（7-4）的新的高可溶性电致磷掺杂剂家族已经合成。已经制备并表征了利用这些配合物的高效，溶液处理的单层电致磷光二极管。高三重态能量聚（9-乙烯基咔唑）PVK用作掺杂有2-（4-联苯基）-5-（4-叔丁基-苯基）-1,3,4-恶二唑（PBD）的主体聚合物电子传输。因此可以实现电流效率为40 cd A1的器件，其EQE为12％。研究了取代基（吸电子基团（CF_3）和供电子基团（OMe））的类型和位置对配合物分子偶极矩的影响。观察到单线态金属-配体电荷转移（〜1MLCT）跃迁的吸收强度与亮度光谱红移随溶剂极性的关系。配合物1-4的跃迁偶极矩的强度也已经从TD-DFT计算中获得，并且发现与观察到的这些配合物的分子偶极矩一致。与电荷载流子散射时间（小于纳秒）相比，磷光激子的寿命较长（微秒），因此过渡偶极矩可被视为“准永久偶极”。因此，载流子迁移率受磷光分子的长寿命跃迁偶极矩充分影响，磷光分子在介质中随机取向。掺杂偶极子由于局部改变的极化能而引起位置和能量紊乱。此外，吸电子基团CF_3引起强的载流子分散，从而增强了电子迁移率。因此，在配合物3和4中的强跃迁偶极矩扰动了电子和空穴迁移率，导致激子形成的减少和器件暗电流的增加，从而降低了器件效率。

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  • 来源
    《Advanced Functional Materials》 |2011年第12期|p.2376-2382|共7页
  • 作者

    Ha meed A. Al-Attar; Careth C. Griffiths; Tom N. Moore; Mustafa Tavasli; Mark A. Fox; Martin R. Bryce; Andrew P. Monkman;

  • 作者单位

    Department of Physics Durham University Durham, DH1 3LE, UK;

    Department of Physics Durham University Durham, DH1 3LE, UK;

    Department of Chemistry Durham University, Durham, DH1 3LE, UK;

    Department of Chemistry Durham University, Durham, DH1 3LE, UK,Uludag Universitesi Fen-Edebiyat Fakultesi, Kimya Bolumu, Gorukle Kampusu 16059 Nilufer, Bursa, Turkiye;

    Department of Chemistry Durham University, Durham, DH1 3LE, UK;

    Department of Chemistry Durham University, Durham, DH1 3LE, UK;

    Department of Physics Durham University Durham, DH1 3LE, UK;

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