Long-Lived Charge-Transfer State and Interfacial Lock in Double-Cable Conjugated Polymers Enable Efficient and Stable Organic Solar Cells.

Abstract

The donor/acceptor (D/A) interfaces in bulk heterojunction (BHJ) organic solar cells (OSCs) critically govern exciton dissociation and molecular diffusion, determining both efficiency and stability. Herein, we design a double-cable conjugated polymer, SC-1F, to insert into a physically-blended D/A system to optimize the interface. We have found that SC-1F spontaneously segregates to the interface through favorable miscibility and heterogeneous nucleation with the acceptor. Its long-lived charge-transfer (CT) state with a lifetime of >3 ns enhances charge generation efficiency in the PM6:BTP-eC9 blend, boosting the power conversion efficiency (PCE) from 19.00% to 20.12%. More importantly, the double-cable nature of SC-1F enables it to be simultaneously miscible with donor and acceptor so as to act as the interfacial lock to prevent their self-aggregation under thermal treatment. Therefore, the PM6:BTP-eC9:SC-1F-based solar cells provided a high T₈₀ of 2175 h compared to a T₈₀ of 530 h based on PM6:BTP-eC9 under 65 °C treatment. Notably, SC-1F-based device demonstrates exceptional storage and thermal stability, with a T₈₀ lifetime exceeding 10 000 h. These results demonstrate the superior advantage of double-cable conjugated polymers as the third component to achieve efficient and stable OSCs.