Light-emitting electrochemical cells (LEECs) are a promising low-cost option for display and solid-state lighting. In these devices, the interplay of mobile ions, electrons, and holes makes for rich physics that can be leveraged for high performance. One example of this interplay is in the formation and radiative decay of excitons-bound electron and hole pairs. Considerations from exciton binding and Langevin recombination suggest that a low dielectric constant (ϵ) would enhance emission. However, emission is also enhanced by the product of the bulk hole and electron concentrations, which in LEECs are enhanced by the motion of small mobile ions yielding high dielectric constants. These competing effects make it difficult to predict whether active layers with low or high dielectric constants will optimize device performance. Here, the effect of varying the dielectric constant on the performance of LEEC devices from ionic transition-metal complexes was studied by systematically exchanging the negative counterions paired with an iridium complex emitter. Electrochemical impedance spectroscopy, constant voltage and constant current device studies, and drift-diffusion simulations were performed. The results clarify the competing effects of Langevin bimolecular recombination and ion-assisted injection processes occurring in LEECs.

中文翻译：

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发光电化学电池中介电常数和离子迁移率的影响。

发光电化学电池（LEEC）是用于显示器和固态照明的有前途的低成本选择。在这些设备中，移动离子，电子和空穴的相互作用使得可以利用丰富的物理特性来实现高性能。这种相互作用的一个例子是受激子结合的电子和空穴对的形成和辐射衰减。激子结合和Langevin重组的考虑表明，低介电常数（ϵ）将增强发射。但是，体孔和电子浓度的乘积也增强了发射，在LEEC中，小移动离子的运动增强了电子的浓度，从而产生了高介电常数。这些竞争效应使得难以预测具有低介电常数或具有高介电常数的有源层将优化器件性能。这里，通过系统地交换与铱配合物发射体配对的负抗衡离子，研究了改变介电常数对离子过渡金属配合物的LEEC器件性能的影响。进行了电化学阻抗谱，恒压和恒流器件研究以及漂移扩散模拟。结果阐明了在LEEC中发生的Langevin双分子重组和离子辅助注射过程的竞争作用。