Charge carrier concentration dependence of encounter-limited bimolecular recombination in phase-separated organic semiconductor blends
Charge carrier concentration dependence of encounter-limited bimolecular recombination in phase-separated organic semiconductor blends
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DOI：
10.1103/physrevb.93.205204
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发表时间：
2016-05-23
影响因子：
3.7
通讯作者：
Deibel, Carsten
中科院分区：
文献类型：
--
作者：
Heiber, Michael C.;Thuc-Quyen Nguyen;Deibel, Carsten
了解有机半导体供体-受体混合物中存在的复杂分子间构型和纳米结构如何影响载流子运动、相互作用和复合行为是一个关键的基本问题，对有机光伏应用产生特别重大的影响。在本研究中，使用动力学蒙特卡罗 (KMC) 模拟对理想化相分离共混物中复杂的双分子载流子复合行为进行数值量化。最近的 KMC 模拟已经确定了这些共混物中的遭遇限制双分子重组率如何偏离常用的 Langevin 模型，并已用于构建新的功率平均迁移率模型。在这里，我们通过确定遭遇限制双分子复合系数的电荷载流子浓度依赖性，对这项工作进行了具有挑战性但至关重要的扩展。在此过程中，我们发现准确处理电荷载流子之间的长程静电相互作用至关重要，并且我们进一步认为，许多先前的 KMC 模拟研究使用的库仑截止半径太小，这导致复合率显着高估。为了进一步阐明这个问题，我们确定了达到小于 +/- 10% 精度所需的最小截止半径，作为域尺寸和载流子浓度的函数，然后利用这些知识来准确量化复合率的载流子浓度依赖性。使用这些严格的方法，我们最终证明功率平均迁移率模型的参数是由新确定的域大小与平均电荷载流子分离距离的无量纲比率决定的。
Understanding how the complex intermolecular configurations and nanostructure present in organic semiconductor donor-acceptor blends impacts charge carrier motion, interactions, and recombination behavior is a critical fundamental issue with a particularly major impact on organic photovoltaic applications. In this study, kinetic Monte Carlo (KMC) simulations are used to numerically quantify the complex bimolecular charge carrier recombination behavior in idealized phase-separated blends. Recent KMC simulations have identified how the encounter-limited bimolecular recombination rate in these blends deviates from the often used Langevin model and have been used to construct the new power mean mobility model. Here, we make a challenging but crucial expansion to this work by determining the charge carrier concentration dependence of the encounter-limited bimolecular recombination coefficient. In doing so, we find that an accurate treatment of the long-range electrostatic interactions between charge carriers is critical, and we further argue that many previous KMC simulation studies have used a Coulomb cutoff radius that is too small, which causes a significant overestimation of the recombination rate. To shed more light on this issue, we determine the minimum cutoff radius required to reach an accuracy of less than +/- 10% as a function of the domain size and the charge carrier concentration and then use this knowledge to accurately quantify the charge carrier concentration dependence of the recombination rate. Using these rigorous methods, we finally show that the parameters of the power mean mobility model are determined by a newly identified dimensionless ratio of the domain size to the average charge carrier separation distance.