π-π Stacking Modulation via Polymer Adsorption for Elongated Exciton Diffusion in High-Efficiency Thick-Film Organic Solar Cells.

Developing efficient organic solar cells (OSCs) with thick active layers is crucial for roll-to-roll printing. However, thicker layers often result in lower efficiency. This study tackles this challenge using a polymer adsorption strategy combined with a layer-by-layer approach. Incorporating insulator polystyrene (PS) into the PM6:L8-BO system creates PM6+PS:L8-BO blends, effectively suppressing trap states and extending exciton diffusion length in the mixed donor domain. Adding insulating polymers with benzene rings to the donor enhances π-π stacking of donors, boosting intermolecular interactions and electron wave function overlap. This results in more orderly molecular stacking, longer exciton lifetimes, and higher diffusion lengths. The promoted long-range exciton diffusion leads to high power conversion efficiencies of 19.05% and 18.15% for PM6+PS:L8-BO blend films with 100 and 300 nm thickness, respectively, as well as a respectable 16.00% for 500 nm. These insights guide material selection for better exciton diffusion, and offer a method for thick-film OSC fabrication, promoting a prosperous future for practical OSC mass production.