Reducing Solvent Selectivity via Solid Additive‐Assisted Strategy Enables Organic Solar Cells With Approaching 21% Efficiency

Currently, high-performance organic solar cells (OSCs) are predominantly fabricated using chloroform (CF) to achieve an optimal active-layer morphology. However, its rapid film formation results in a narrow processing window and severely limits industrial scalability. Therefore, reducing solvent selectivity during active-layer processing is essential to facilitate scalable OSC manufacturing. Herein, this critical issue is finely addressed by a solid-additive-assisted strategy, in which 2,6-dimethylnaphthalene (2,6-DMN) is incorporated to modulate the film formation dynamic and molecular aggregation in different processing solvents. It is revealed that 2,6-DMN enables stage-specific control over the film formation process. Its mechanism involves suppressing acceptor aggregation during spin-coating and then promoting ordered acceptor self-assembly during annealing. This two-stage modulation simplifies donor-acceptor interactions, mitigates excessive aggregation caused by slow solvent drying, and thereby prevents large-scale phase separation. As a result, 2,6-DMN induces a highly uniform and favorable active-layer morphology across various processing solvents, thereby alleviating performance variations in devices caused by solvent effect. Consequently, the 2,6-DMN-based PM6:D18:L8-BO-X ternary device processed from o-xylene achieves a remarkable efficiency of 20.86%, setting a record for non-halogenated solvent-processed OSCs. This work provides a practical and efficient solid-additive-assisted strategy to mitigate the solvent selectivity in OSCs, demonstrating significant potential for achieving high-performance OSCs with enhanced processing compatibility.