Improving Photovoltaic Performance of Non‐Fullerene Polymer Solar Cells Enables by Fine‐Tuning Blend Microstructure via Binary Solvent Mixtures

Abstract Studies of the relationship between blend microstructure and photovoltaic performance are becoming more common, which is a prerequisite for rationally improving device performance. Non‐fullerene acceptors usually have planar backbone conformation and strong intermolecular packing, normally resulting in excessive phase separation. Herein, an effective co‐solvent blending strategy to turn the molecular organization of a chlorinated small molecule acceptor Y6‐2Cl and phase separation of the corresponding active layer with PM6 as donor is demonstrated. The in situ photoluminescence measurements and relevant morphological characterizations illustrate that the film‐forming process is fine‐turned when using the mixtures of chloroform (CF) and chlorobenzene (CB) solvents, and the blend showed high domain purity with suitable phase‐separated networks. Thus, better exciton dissociation and charge generation, more balanced charge transport, and less recombination loss are obtained in the co‐solvent blade‐coated devices. As a result, a maximum power conversion efficiency (PCE) of 16.17% is achieved, which is much higher than those of CF‐ and CB‐bladed devices (14.08% and 11.44%, respectively). Of note is that the use of this co‐solvent approach in the other two high‐performance photovoltaic systems is also confirmed, demonstrating its good generality of employing in the printing organic solar cells.