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

Abstract

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.