The detrimental impact of non-geminate recombination on high-performance organic photovoltaics has been recognised and primarily attributed to bimolecular recombination. However, the recent surge in Y-series acceptor-based systems has drawn attention to deep-trap-assisted monomolecular recombination. This study reveals the morphological origin of deep traps in the prototypical PM6:Y6 system, identifying isolated crystalline and amorphous Y6 domains as key contributors. The findings underscore the importance of improving inter-acceptor domain connectivity for effective trap passivation. For the first time, we have pinpointed a crucial metric for inversely quantifying the inter-acceptor domain connectivity: the crystalline domain fractal dimension (D_f). Due to the self-similar nature of fractal structures, the fractal dimension propagates across multi-length scales and can be controlled by tuning local intermolecular aggregation motifs. Remarkably, combining diiodide benzene (DIB) as the additive and layer-by-layer (LBL) processing effectively promotes the more extended backbone order of Y6 molecules, consequently reducing the fractal dimensions and passivating deep traps. By applying this strategy to another high-performance system, D18:L8BO, a benchmark efficiency of 19.6% is achieved, among the highest efficiencies reported for LBL OPVs.

中文翻译：

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通过减小分形维数来增强域间连接性：钝化有机光伏中深陷阱的关键


非双分子复合对高性能有机光伏的有害影响已经得到认可，主要归因于双分子复合。然而，最近基于 Y 系列受体的系统的激增引起了人们对深陷阱辅助单分子重组的关注。本研究揭示了原型 PM6：Y6 系统中深陷阱的形态起源，确定了孤立的结晶和非晶态 Y6 结构域是关键贡献者。研究结果强调了改善受体域间连接以实现有效陷阱钝化的重要性。我们首次确定了逆量化受体域间连接的关键指标：晶体域分形维数 （D_f）。由于分形结构的自相似性质，分形维数在多长度尺度上传播，并且可以通过调整局部分子间聚集基序来控制。值得注意的是，将二碘化苯 （DIB） 作为添加剂和逐层 （LBL） 加工相结合，有效地促进了 Y6 分子的更扩展的主链顺序，从而降低了分形维度并钝化了深陷阱。通过将这种策略应用于另一个高性能系统 D18：L8BO，实现了 19.6% 的基准效率，是 LBL OPV 报告的最高效率之一。