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

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.

Automated summary

This study demonstrates an effective co-solvent blending strategy to improve the molecular organization of a chlorinated small molecule acceptor and phase separation with the corresponding donor, leading to improved photovoltaic performance.