Solvent-driven backbone chain distribution in bulk of P3HT film: Effect on the microstructure via molecular dynamics simulations

Regioregular poly(3-hexylthiophene) (P3HT) thin films are commonly used as a benchmark for evaluating new p-type or donor conjugate molecules. However, predicting the electronic behavior of organic semiconductors remains challenging due to the sensitivity of their electronic structure to both molecular configuration and intermolecular interactions. These factors are strongly influenced by various processing parameters, including the choice of solvent. In this work, we used molecular dynamics simulations to investigate the effects of solvent on the microstructure of films produced via an assisted solvent evaporation methodology, focusing on 1,2-dichlorobenzene (ODCB) and 1,2,4-trichlorobenzene (TCB). The results revealed that the lowest solubility in P3HT, attributed to TCB, produced a film with a crossing distribution of the backbone chains throughout the film, with no preferential direction. Conversely, the ODCB-processed film promoted a more parallel alignment of the chains, yielding a more anisotropic profile. These differences in solvent-induced chain organizations influenced the intermolecular π-π stacking interactions between thiophene units, thereby shaping the distinctive microstructures obtained for each film. Our findings are consistent with photoemission microscopy measurements reported in the literature. This contribution presents a modeling approach able to distinguish the microstructures of P3HT films processed by different solvents, as well as a molecular-level understanding of how solvents with distinct solubilities for P3HT affect the microstructures of the films.