Organic solar cells offer several advantages over conventional photovoltaics, such as flexibility, low cost, and abundant materials, and are thus seen as a promising choice for energy harvesting. A rather particular case refers to diluted systems, where a small number of electron-donating molecules are dispersed within an acceptor matrix, hampering hole transport in the absence of percolation paths. Nonetheless, diluted systems present a reasonable performance, thereby raising discussions on how this is achieved. Here, we investigate the hole transport by measuring the hole mobility in several systems with varying donor concentrations. We found an unexpected correlation between the hole mobility and the energy offset between the donor HOMO and the acceptor LUMO (instead of the acceptor HOMO), with the mobility increasing as the offset decreases. Such a correlation is supported by molecular modeling suggesting a contribution from the acceptor LUMO-mediated superexchange mechanism. These results corroborate our experimental observation, hinting at a previously neglected mechanism of transport, which depends on the coupling between the donor HOMO and the acceptor LUMO.

中文翻译：

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低施主含量有机太阳能电池中受主性质对空穴传输机制的作用

有机太阳能电池与传统光伏发电相比具有多种优势，例如灵活性、低成本和丰富的材料，因此被视为能量收集的有前途的选择。一个相当特殊的情况是指稀释系统，其中少量给电子分子分散在受体基质内，在没有渗滤路径的情况下阻碍空穴传输。尽管如此，稀释后的系统仍表现出合理的性能，从而引发了关于如何实现这一目标的讨论。在这里，我们通过测量具有不同供体浓度的几个系统中的空穴迁移率来研究空穴传输。我们发现空穴迁移率与供体 HOMO 和受体 LUMO（而不是受体 HOMO）之间的能量偏移之间存在意想不到的相关性，迁移率随着偏移量的减小而增加。这种相关性得到了分子模型的支持，表明受体 LUMO 介导的超交换机制的贡献。这些结果证实了我们的实验观察，暗示了以前被忽视的运输机制，该机制取决于供体 HOMO 和受体 LUMO 之间的耦合。