Molecular-Weight-Regulated Aggregation Kinetics Enables Additive-Free Morphology Control for High-Efficiency and Scalable Organic Solar Cells

Journal article, 2026

Controlling active-layer morphology without processing additives remains a core challenge for high-efficiency organic solar cells (OSCs), particularly for molecular-weight-sensitive polymer donors. Here, we report an additive-free morphology control strategy based on molecular-weight-mediated aggregation kinetics using the benchmark donor polymer D18. We show that both low- and high-molecular-weight D18 exhibit aggregation behavior mismatched to the nonfullerene acceptor L8-BO, causing to suboptimal film formation. By blending D18 with different molecular weights, the donor aggregation time window is broadened and moderated, enabling kinetically synchronized film formation without additive assistance. As a result, additive-free D18-mix:L8-BO devices deliver a high power conversion efficiency of 20.0% with balanced charge transport and suppressed recombination, while maintaining efficiencies above 19% over a wide blending range. Moreover, this intrinsic kinetic regulation strategy is compatible with advanced device architectures and scalable fabrication: ternary D18-mix:L8-BO:AITC devices achieve an enhanced efficiency of 20.5%, and large-area modules (17.14 cm²) retain an efficiency of 17.2%. This work establishes molecular weight as an intrinsic kinetic handle for additive-free morphology control, offering a robust and scalable materials strategy for high-performance OSCs.