Recombination of free charges is a key loss mechanism limiting the performance of organic semiconductor-based photovoltaics such as solar cells and photodetectors. The carrier density-dependence of the rate of recombination and the associated rate coefficients are often estimated using transient charge extraction (CE) experiments. These experiments, however, often neglect the effect of recombination during the transient extraction process. In this work, the validity of the CE experiment for low-mobility devices, such as organic semiconductor-based photovoltaics, is investigated using transient drift-diffusion simulations. We find that recombination leads to incomplete CE, resulting in carrier density-dependent recombination rate constants and overestimated recombination orders; an effect that depends on both the charge carrier mobilities and the resistance–capacitance time constant. To overcome this intrinsic limitation of the CE experiment, we present an analytical model that accounts for charge carrier recombination, validate it using numerical simulations, and employ it to correct the carrier density-dependence observed in experimentally determined bimolecular recombination rate constants.

中文翻译：

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理解无序半导体中复合限制电荷提取的新框架

自由电荷的重组是限制太阳能电池和光电探测器等有机半导体光伏器件性能的关键损失机制。复合速率和相关速率系数的载流子密度依赖性通常使用瞬态电荷提取（CE）实验来估计。然而，这些实验常常忽略瞬时提取过程中重组的影响。在这项工作中，使用瞬态漂移扩散模拟研究了低迁移率器件（例如基于有机半导体的光伏器件）的 CE 实验的有效性。我们发现复合导致不完全的CE，导致载流子密度依赖的复合速率常数和高估的复合阶数；该效应取决于载流子迁移率和电阻电容时间常数。为了克服 CE 实验的这一固有局限性，我们提出了一种解释载流子复合的分析模型，使用数值模拟对其进行验证，并利用它来校正在实验确定的双分子复合速率常数中观察到的载流子密度依赖性。