A small molecule donor dimer interconnected by a benzo[1,2-b:4,5-b′]dithiophene central unit side chain enables highly efficient and thermally stable all-giant-molecule solar cells

The low phase-transition temperatures (Tpts) of structurally defined small molecules impose fundamental limitations on thermal stability in all-small-molecule (all-SM) systems. To overcome this, we designed and synthesized a dimeric donor, DM-2Cl, interconnected by a benzo[1,2-b:4,5-b′]dithiophene central unit side chain, and combined it with the giant molecule acceptor, BDY-β, to construct a conceptual all-giant-molecule (all-GM) system with enhanced solid-state Tpt. The DM-2Cl:BDY-β system suppressed morphology evolution under continuous thermal-annealing and demonstrated superior stability relative to the BDT-1S1Cl:Y6 reference. Crucially, optimized blend morphology and improved charge transport/extraction properties enabled the binary all-GM system to achieve a 15.56% PCE, which increased to 16.24% upon incorporating giant-molecule acceptor Se-giant-2F. This work paves the way to design dimeric donors, introducing new all-giant-molecule systems with high device efficiency and excellent thermal stability.