Benzo[1,2-b:4,5-b']difuran-Based Polymer Donor with Chlorophenyl Side Chains Achieving High-Performance Organic Solar Cells.

The advances in high-performance polymer donors are significant for realizing efficient organic solar cells (OSCs). At present, the majority of polymer donors in top-performing OSCs utilize benzo[1,2-b:4,5-b']dithiophene (BDT) units, whereas structurally similar benzo[1,2-b:4,5-b']difuran (BDF)-based polymers remain less explored due to their lower efficiencies. Here, we designed and synthesized a polymer donor named PBDF-CB by incorporating chlorophenyl BDF as the electron-donating unit and fluorinated benzotriazole as the electron-accepting unit. PBDF-CB displays a deep highest occupied molecular orbital (HOMO) energy level of -5.62 eV and a suitable self-assembly fibrillar structure, conducive to elevating open-circuit voltage (Voc) and improving charge transport in devices. As an asymmetrical molecule, LC301 with a high lowest unoccupied molecular orbital (LUMO) energy level is employed as the acceptor, and the devices based on PBDF-CB attain an impressive efficiency of 19.10% with a Voc of 0.911 V and a fill factor of 79.1%. In contrast, PBDT-CB:LC301 photovoltaic devices can only reach 15.93% because of negative molecular packing ordering and excessive miscibility between donor and acceptor materials. These results underscore the significant potential of BDF-based polymer donors for achieving high-performance OSCs.