Impact of molecular structure on the properties of charge transfer states and energy disorder in organic solar cells

The charge transfer (CT) states formed at donor-acceptor interfaces play a key role in determining exciton dissociation, charge separation and recombination. To improve the power conversion efficiency of organic solar cells, it is essential to enhance exciton dissociation while reducing recombination. In this study, we selected P3HT: PCBM and PM6:Y6 as research objects. By combining molecular dynamics simulations and long-range corrected density functional theory calculations, a deeper understanding of the relationship between molecular structure of donor/acceptor, CT properties and exciton dissociation rates/recombination rates has been achieved. Results show that PCBM has a unique three-dimensional spherical structure. This structure allows P3HT chains with large torsional angles to bend more easily around PCBM molecules, forming spatial barriers that hinder π–π packing and limit exciton dissociation at donor/acceptor interfaces. Additionally, energy disorder in CT states mainly arises from structural variations in P3HT backbones. These effects together lead to higher nonradiative voltage losses and lower exciton dissociation rates in P3HT: PCBM blend, whereas PM6:Y6 blend shows superior exciton dissociation and reduced nonradiative voltage loss.