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<p>Balancing bulk and interfacial charge dynamics is essential for advancing the performance of organic solar cells (OSCs). However, most prior studies have predominantly targeted the suppression of bulk recombination, while interfacial losses have received comparatively limited attention. Here, we present an additive-isomerism strategy that enables simultaneous regulation of bulk morphology and interfacial properties. Specifically, we employ three positional isomers of solid 4-bromochlorobenzene (BCB), together with two liquid analogues derived from ortho-BCB (<i>o</i>-BCB) and meta-BCB (<i>m</i>-BCB), to systematically elucidate how substitution geometry influences phase separation, surface roughness, and charge recombination in PM6:BTP-eC9 OSCs. Despite sharing an identical molecular formula, these additives yield markedly different optoelectronic behaviours. The solid BCB enhances bulk crystallization and promotes efficient exciton dissociation, yet its coarse phase morphology intensifies interfacial recombination. By contrast, the liquid isomers generate smoother surfaces and effectively suppress interfacial charge losses. Among them, <i>m</i>-BCB provides the most favorable balance between robust bulk charge transport and minimized interfacial recombination, delivering a power conversion efficiency of 20.62%. This work establishes additive isomerism as a versatile approach for concurrently optimizing charge dynamics across multiple length scales and offers new insights into suppressing recombination losses through morphology engineering in OSCs.</p>

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Molecular positional isomerism of volatile additives enables multi-scale recombination control in organic solar cells

  • 期刊论文

  • 发表日期：

    2026年4月30日

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  • Panpan Zhang,
  • Keteng Zhu,
  • Haijun Bin,
  • Jing Zhang,
  • Chaohua Cui,
  • Yongfang Li

摘要

Balancing bulk and interfacial charge dynamics is essential for advancing the performance of organic solar cells (OSCs). However, most prior studies have predominantly targeted the suppression of bulk recombination, while interfacial losses have received comparatively limited attention. Here, we present an additive-isomerism strategy that enables simultaneous regulation of bulk morphology and interfacial properties. Specifically, we employ three positional isomers of solid 4-bromochlorobenzene (BCB), together with two liquid analogues derived from ortho-BCB (o-BCB) and meta-BCB (m-BCB), to systematically elucidate how substitution geometry influences phase separation, surface roughness, and charge recombination in PM6:BTP-eC9 OSCs. Despite sharing an identical molecular formula, these additives yield markedly different optoelectronic behaviours. The solid BCB enhances bulk crystallization and promotes efficient exciton dissociation, yet its coarse phase morphology intensifies interfacial recombination. By contrast, the liquid isomers generate smoother surfaces and effectively suppress interfacial charge losses. Among them, m-BCB provides the most favorable balance between robust bulk charge transport and minimized interfacial recombination, delivering a power conversion efficiency of 20.62%. This work establishes additive isomerism as a versatile approach for concurrently optimizing charge dynamics across multiple length scales and offers new insights into suppressing recombination losses through morphology engineering in OSCs.