Balancing Solvent Polarity and Drying‐Kinetics for Processing Nonfullerene Acceptors Toward High‐Performance Organic Solar Cells

In recent years, the emergence of high‐efficiency nonfullerene acceptors (NFAs) has pushed the power conversion efficiency (PCE) beyond 19% in organic solar cells (OSCs). For solution processing of the photoactive layers, the study of solvent properties on device performance has become a hot research topic toward up‐scaling. Herein, the key roles of balancing solvent polarity and drying kinetics for processing of small molecular NFAs toward high‐performance OSCs are revealed. It is demonstrated that the synergistic effect of solvent polarity and drying kinetics significantly affects the multilength scale morphology of solid films and photovoltaic performance. Furthermore, the self‐assembly of NFAs in solution and the resulting thin film microstructures induced by electrostatic interactions with polarized additives are even more sensitive to solvent polarity and drying kinetics. Finally, the optimized devices achieve an outstanding PCE of 18.54% by fine‐tuning the microstructure with polar solvent and fast‐drying kinetics to form improved molecular packing and structure size. The work provides a novel view and deeper insights into the general selection rules of solvents toward the solution processing of high‐performance nonfullerene OSCs.