Dihedral Restrained Molecular Dynamics Aligns Simulated and Experimental Crystallinity in Organic Solar Cells

Organic solar cells (OSCs) present an efficient, low-cost alternative for renewable energy applications, with recent advancements driven by the development of nonfullerene acceptors (NFAs) that have significantly improved the power conversion efficiency (PCE) of OSCs to over 20%, narrowing the performance gap with other types of solar cells. The molecular stacking in the active layer is crucially important for highly efficient energy conversion; however, experimental techniques still face limitations in capturing the detailed structural information at the molecular level. To address this challenge, molecular dynamics (MD) simulations could provide atomistic insight into molecular configurations, offering opportunities to optimize the morphology in the active layer. Despite this, achieving experimentally accurate crystalline arrangements and domains within reasonable computational timeframes remains difficult. In this work, we have systematically investigated the influence of dihedral angle restraints in MD simulations based on the representative NFA, CH17, and Y6. It is found that dihedral restraints lead to more ordered molecular stacking with monomer, dimer, and long-range structures closely resembling the crystalline arrangements. Additionally, we confirmed that CH17 exhibits stronger π-π stackings compared to Y6, further validating its superior PCE. Our study highlights the important potential of dihedral angle restraints in improving the accuracy of molecular simulations, which offers valuable insights for the designing of high-performance OSC materials.