Decoding Morphological Control in Isomeric Non-Fullerene Acceptor–Polymer Blends for Organic Solar Cells

Optimizing organic solar cells necessitates a fundamental understanding of how noncovalent interactions influence the miscibility and stability of nonfullerene acceptor (NFA)–polymer blends. In this study, we employ molecular simulations combined with data-driven analysis to elucidate the impact of regioisomerism on phase morphology in Y-series fused-ring NFAs. Specifically, we compare a C-shaped isomer (CF) and an S-shaped isomer (SF) when blended with the donor polymer D18. Our findings reveal that the CF blend exhibits superior miscibility, attributed to stronger van der Waals interactionsincluding hydrogen bonding and interactions involving sulfur and electronegative atomsas well as enhanced dipole–dipole interactions. These interactions collectively contribute to greater blend stability, as supported by noncovalent interactions and energy decomposition analyses. Furthermore, k-means clustering of molecular dynamics trajectories was employed to assess miscibility, corroborating the superior miscibility of the CF blend, while the SF blend demonstrated phase segregation. Voronoi tessellation analysis provides a geometric perspective, linking uniform molecular packing in the CF blend to minimal void spaces, whereas the SF blend exhibits structural heterogeneity and aspherical cavities. These insights establish a direct connection among isomeric configuration, intermolecular forces, and blend morphology, offering a predictive framework for designing high-performance organic solar cells.