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Shedding Light on the Operation of Polymer Light-Emitting Electrochemical Cells Using Impedance Spectroscopy

机译：运用阻抗光谱研究聚合物发光电化学电池的运作

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摘要

A combination of impedance spectroscopy, device characterization, and modeling is used to pinpoint key processes in the operation of polymer light-emitting electrochemical cells (LECs). At low applied voltage, electric double layers with a thickness of ≈2-3 nm are shown to exist at the electrode interfaces. At voltages exceeding the bandgap potential of the conjugated polymer (V≥ 2.5 V for superyellow), a light-emitting p-n junction forms in situ, with a steadystate structure that is found to depend strongly on the applied voltage. This is exemplified by that the effective p-n junction thickness (d_(pn)) for a device with an interelectrode gap of 90 nm decreases from ≈23 nm at 2.5 V to ≈6 nm at 3.9 V. The current increases with decreasing d_(pn) in a concerted manner, while the brightness reaches its peak at V= 3.4 V when d_(pn) ≈ 10 nm. The existence of an optimum d_(pn) for high brightness in LECs is attributed to an offset between an increase in the exciton formation rate with decreasing d_(pn) due to an increasing current, and a simultaneous decrease in the exciton radiative decay rate, when an increasing fraction of excitons diffuses away from the p-n junction into the surrounding non-radiative doping regions.
机译：在聚合物发光电化学电池（LEC）的操作中，结合使用了阻抗光谱法，器件表征和建模技术来确定关键过程。在低施加电压下，电极界面处存在厚度约为2-3 nm的双电层。在超过共轭聚合物的带隙电势的电压下（对于超黄色，V≥2.5 V）会在原位形成发光的p-n结，其稳态结构在很大程度上取决于所施加的电压。这可以通过电极间间隙为90 nm的器件的有效pn结厚度（d_（pn））从2.5 V的≈23nm减小到3.9 V的≈6nm来体现。电流随着d_（pn的减小）而增加），当d_（pn）≈10 nm时，亮度达到V = 3.4 V的峰值。 LEC中高亮度的最佳d_（pn）的存在归因于激子形成速率的增加与电流增加引起的d_（pn）的减小之间的抵消与激子辐射衰减率的同时降低之间的抵消，当越来越多的激子从pn结扩散到周围的非辐射掺杂区时。

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  • 来源
    《Advanced Functional Materials》 |2012年第7期|p.1511-1517|共7页
  • 作者

    Antoni Munar; Andreas Sandstroem; Shi Tang; Ludvig Edman;

  • 作者单位

    Department of Physics Umea University SE-90187 Umea, Sweden,Department of Physics Universitat Jaume-I Castello de la Plana, 12071, Spain;

    Department of Physics Umea University SE-90187 Umea, Sweden;

    Department of Physics Umea University SE-90187 Umea, Sweden;

    Department of Physics Umea University SE-90187 Umea, Sweden;

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