Regulating pre-aggregation in non-halogenated solvent to enhance the efficiency of organic solar cells

Optimizing the morphology of an active layer in organic solar cells (OSCs) through precise control of precursor solution aggregation is a crucial step in enhancing photovoltaic performance. However, the considerable difference in solubility among organic materials in environmentally friendly solvents, such as non-halogenated solvents, poses a challenge in simultaneously modulating the pre-aggregation of both donor and acceptor. Herein, we employ a synergistic approach that involves heat treatment and the addition of a solid additive to regulate the aggregation behavior of PM6 (donor) and BTP-ec9 (acceptor) within an o-xylene solvent. Our findings reveal that PM6 exhibits strong temperature-dependent aggregation tendencies, while the solid additive 1,4-diiodobenzene (DIB) notably influences the aggregation of BTP-ec9. Thus, treating the precursor solution at 90 °C and adding DIB result in a well-matched aggregation between donor and acceptor, effectively optimizing the crystallization and phase separation morphology of the active layer. This strategic intervention leads to an outstanding efficiency of 18.07%, with a fill factor of 78.65%, for the corresponding device, which ranks among the highest efficiencies for the non-halogenated solvent-processed OSCs. Importantly, this study also demonstrates the feasibility of fabricating thick-film and large-area OSCs by blade-coating, achieving efficiencies of 16.15% and 15.29%, showcasing substantial potential for commercial applications.