Precise Alkyl Chain Tuning of Dibromoalkane Additives Enables Efficient Organic Solar Cells with Minimal Voltage Loss

While solvent additive engineering is a widely adopted strategy for morphological optimization in organic solar cells (OSCs), conventional high-boiling-point additives often induce excessive molecular aggregation and aggregation-caused quenching (ACQ), which deteriorate electroluminescence quantum efficiency (EQE_EL) and exacerbate nonradiative recombination. Herein, we overcome this trade-off by precisely modulating the alkyl chain length of dibromoalkane additives to decouple energetic disorder from nonradiative losses. Through a systematic investigation of a homologous series, 1,4-dibromobutane (DBrB), 1,6-dibromohexane (DBrH), and 1,8-dibromooctane (DBrO), we demonstrate that DBrH uniquely optimizes intermolecular packing while maintaining low energetic disorder and suppressing ACQ. In contrast, shorter-chain DBrB provides insufficient kinetic control, whereas longer-chain DBrO triggers excessive aggregation and severe nonradiative recombination. Leveraging this chain-length-dependent design principle, DBrH enables a performance of 19.1% in PM6:BTP-eC9 binary devices without compromising open-circuit voltage and further exhibits excellent universality in ternary blends, achieving 20.0% efficiency in the PM6:L8-BO:L8-BO-F system. This work establishes alkyl chain length tuning as a precise and generalizable strategy for simultaneously minimizing energetic disorder and nonradiative voltage losses in high-performance OSCs.