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

ABSTRACT

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.