Tuning Intermolecular Interactions With Solid Additives to Optimize Molecular Aggregation and Molecular Packing in All‐Polymer Solar Cells

All-polymer solar cells (all-PSCs) suffer from significant challenges of large-scale aggregation and phase separation due to poor compatibility between donor and acceptor polymers. In this study, we introduce volatile solid additives to regulate intermolecular interactions and improve blending miscibility, thereby controlling aggregation and phase separation. Both computational and experimental results reveal that the key to this regulation lies in the strong electrostatic potential coupling between the solid additive and the polymer acceptor. This selective interaction modulates the aggregation behavior during film deposition and thermal annealing, enabling a gradual phase evolution. Further analysis indicates that the strong electrostatic coupling reduces aggregate size and promotes more ordered molecular packing, ultimately optimizing the film morphology. As a result, all-PSCs based on PM6/PY-IT incorporating the solid additive 2-BDBF exhibit a significantly improved power conversion efficiency of 18.62%, representing an increase compared to 14.93% ender the control conditions. This work demonstrates that solid additives with engineered electrostatic interactions offer an effective strategy to tune intermolecular forces, optimize morphology evolution, and boost device performance in all-PSCs.