Among the parameters that characterize a solar cell and define its power-conversion efficiency, the fill factor is the least well understood, making targeted improvements difficult. Here we quantify the competition between charge extraction and recombination by using a single parameter θ, and we demonstrate that this parameter is directly related to the fill factor of many different bulk-heterojunction solar cells. Our finding is supported by experimental measurements on 15 different donor:acceptor combinations, as well as by drift-diffusion simulations of organic solar cells in which charge-carrier mobilities, recombination rate, light intensity, energy levels and active-layer thickness are all varied over wide ranges to reproduce typical experimental conditions. The results unify the fill factors of several very different donor:acceptor combinations and give insight into why fill factors change so much with thickness, light intensity and materials properties. To achieve fill factors larger than 0.8 requires further improvements in charge transport while reducing recombination.

中文翻译：

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重组和自由电荷提取之间的竞争决定了有机太阳能电池的填充因子。

在表征太阳能电池并定义其功率转换效率的参数中，填充因子了解得最少，因此难以有针对性地进行改进。在这里，我们通过使用单个参数θ来量化电荷提取和重组之间的竞争，并且证明了该参数与许多不同的体-异质结太阳能电池的填充因子直接相关。我们的发现得到了对15种不同供体：受体组合的实验测量以及有机太阳能电池的漂移-扩散模拟的支持，其中电荷载流子迁移率，复合率，光强度，能级和活性层厚度均发生了变化在宽范围内重现典型的实验条件。结果统一了几个非常不同的捐助者的填充因子：受体组合并深入了解填充因子为何随厚度，光强度和材料特性发生如此大的变化。为了实现大于0.8的填充因子，需要进一步改善电荷传输，同时减少重组。