Designed Polymer Donors to Match an Amorphous Polymer Acceptor in All-Polymer Solar Cells

All-polymer solar cells (all-PSCs) based on amorphous polymer acceptors show different phase separation behaviors from those with conventional semicrystalline polymer acceptors. In this work, to match an amorphous polymer acceptor, we have designed three polymer donors with the same conjugated backbone poly(benzo[1,2-b:4,5b']dithiophene (BDT)-co-4,7-dithiophene-5,6-didecyloxylbenzo[2,1,3]thiadiazole) but with zero, two, or four fluorine substitutes on the side chains. The increasing number of fluorine substituents leads to downshifted LUMO/HOMO energy levels and more serious aggregation behavior of the polymer donors. The polymer bearing four fluorine substitutes (PD-4F) matches well with the amorphous polymer acceptor. Benefiting from the optimal phase separation morphology, improved charge transport, and suppressed charge recombination, the PD-4F-based all-PSC device shows the highest device performance with a power conversion efficiency of 6.45%. These results indicate an effective approach of side chain fluorination to design polymer donors to match amorphous polymer acceptors for efficient all-PSCs.