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. The solvent polarity and film drying kinetics have a synergistic effect on thin film microstructure and exciton/charge carrier dynamics. After establishing the relationship between polarity-processing-function, the aggregation behavior of small molecule nonfullerene acceptors in solution is further regulated by introducing electrostatic interactions, which demands fine-tuning of the polarity and drying kinetics for enhancing device performance.image (c) 2024 WILEY-VCH GmbH