Suppression of exciton–vibration coupling via modulated insulator dilution for thickness-tolerant organic solar cells

Developing thickness-tolerant organic solar cells (OSCs) is imperative for scalable roll-to-roll fabrication, yet prevalent systems suffer from severe efficiency losses at increased active-layer thicknesses. Strong exciton-vibration coupling critically impedes exciton transport and triggers detrimental non-radiative recombination in thick films, curtailing exciton diffusion length. Herein, we propose a modulated insulator dilution (MID) strategy, employing tailored molecular weight polypropylene (PP), to achieve high-performance OSCs with exceptional thickness tolerance. Driven by a polymer swelling effect during processing, PP incorporation orders acceptor molecular packing, optimizing fibrous nanomorphology and enhancing π-π interactions within PM6:L8-BO systems. This MID approach effectively suppresses exciton-vibration coupling and optimizes excited-state dynamics. By localized-to-delocalized exciton diffusion enhancement, PP incorporation boosts the efficiency of a 500 nm device to 15.92%, which is one of the highest values among 500 nm OSCs. Efficiency remains substantial (∼12%) even at a challenging 1-μm thickness. This work underscores molecular weight-modulated insulator dilution as a pivotal strategy for exciton management and performance enhancement, providing a crucial pathway toward the industrialization of organic photovoltaics.