Coarse‐Grained Molecular Dynamics Study on Naphthalene‐Based Solid Additives for Optimizing Morphology in PM6: PYIT Organic Solar Cells

ABSTRACT The use of solid additives is crucial for optimizing blend morphology and enhancing power conversion efficiency (PCE) in organic photovoltaics (OPVs). This study investigates four naphthalene‐derived additives (2‐chloronaphthalene (2‐CN), 2‐methylnaphthalene (2‐MN), 2‐methylthionaphthalene (2‐sMN), and 2‐methoxynaphthalene (2‐oMN)) in PM6:PYIT blends via coarse‐grained molecular dynamics simulations. Results show that these additives effectively regulate morphology and microstructure. Specifically, 2‐CN strengthens π – π stacking among PM6 molecules and enriches the PM6 phase, while 2‐MN significantly enhances phase separation between PM6 and PYIT. In contrast, 2‐sMN and 2‐oMN exhibit weaker effects due to steric hindrance from their substituents. This work demonstrates that substituent engineering in naphthalene derivatives can selectively tune π – π stacking and phase separation. The chlorine group in 2‐CN enhances intermolecular interactions, and the methyl group in 2‐MN promotes phase separation with minimal steric hindrance. Meanwhile, bulkier ─SCH 3 and ─OCH 3 groups impede similar improvements. Such synergistic mechanisms contribute to optimized morphology and improved PCE in OPVs.