Flexible Linker Engineering of Dimeric Acceptors Enables Synergistic Modulation of Dielectric Constant and Spatial Conjugation for Organic Solar Cells Exceeding 20% Efficiency.

The performance of organic solar cells (OSCs) is predominantly constrained by the low dielectric constants of organic semiconductors, which limit exciton dissociation and exacerbate charge recombination. In particular, dimeric acceptor molecules (DMAs) typically suffer from insufficient short-circuit current density and fill factor, severely restricting the power conversion efficiencies (PCE) of DMA-based devices. Herein, we report a novel flexible linker engineering strategy to construct a series of DMA materials. Starting from CH8-12 with an alkyl flexible linker, we introduce oxygen atoms at the β‑position of the alkyl flexible linker to obtain CH8‑13. Further fluorine decoration on the monomer wings is implemented to yield CH8-14. Such dual modification strategies simultaneously elevate the dielectric constant and optimize the spatial conjugation of flexible-linked dimeric acceptors. The PM6:CH8‑14 binary device achieved a breakthrough PCE exceeding 20%, which represents the highest efficiency among all reported DMA-based binary organic solar cells. Besides, CH8-14 based ternary devices obtained a high PCE of 20.42%. Impressively, the flexible device delivers a prominent PCE of 18.53% with excellent mechanical properties. This work demonstrates the great potential and essential significance of rational linker modulation, offering feasible design principles for the development of advanced DMA materials and high-efficiency organic photovoltaics.