Effect of Solvent Additives on the Solution Aggregation of Phenyl-C₆₁-Butyl Acid Methyl Ester (PCBM)

High-boiling-point solvent additives, employed during the solution processing of active-layer formulations, impact the efficiency of bulk heterojunction (BHJ) organic solar cells by influencing the morphological/topological features of the multicomponent thin film. Here, we aim at a better understanding of how these additives change the aggregation landscape in the casting solution prior to film deposition via a multiscale computational study of the aggregation phenomena of phenyl-C₆₁-butyric-acid methyl ester (PCBM) in various solutions. The energetic landscape of PCBM-solvent/solvent-additive intermolecular interactions is evaluated at the electronic-structure level through symmetry-adapted perturbation theory to determine the nature and strength of noncovalent forces important to aggregation. Molecular dynamics simulations highlight how the choice of solvent and solvent additives control the formation of molecular aggregates. Our results indicate that high-boiling point solvent additives change the effective interactions among the PCBM and casting-solvent molecules and alter equilibrium PCBM aggregate size in solution.