Donor‐Selective NiCo‐LDH Templating Directs Polymer Assembly for Enhanced Exciton Transport in Efficient Organic Solar Cells

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Organic solar cells (OSCs) have achieved remarkable progress, yet improving exciton utilization in polymer donors remains challenging due to their intrinsically limited exciton diffusion length ( L D ). Here, we report a donor‐selective templating strategy based on few‐layer‐like nickel–cobalt layered double hydroxide (NiCo‐LDH) nanosheets to regulate polymer donor assembly in OSCs. The hydroxyl‐rich NiCo‐LDH surface exhibits preferential affinity toward polymer donors and promotes ordered donor‐chain organization during film formation, while exerting limited influence on the acceptor component. This templating strategy enhances the molecular ordering of the donor phase and increases the L D of D18 from 10.7 to 18.9 nm, accompanied by the formation of more ordered donor fibrillar structures. The coordinated improvements in donor organization and exciton transport are further associated with enhanced exciton‐to‐charge conversion, more balanced carrier transport, and suppressed recombination. Consequently, D18:L8‐BO‐based OSCs achieve a maximum power conversion efficiency (PCE) of 21.36%, independently certified at 21.09%, together with improved stability under continuous illumination. Analogous donor‐biased interactions, enhanced exciton diffusion, regulated fibrillar organization, and improved photovoltaic performance are also observed in PM6 and D18‐Cl systems. These results highlight the broader applicability of chemically active 2D templating for coordinating polymer donor assembly and exciton transport toward high‐performance OSCs.