Herein, by using two fluorinated and chlorinated monomers
with
similar structures in different molar ratios and dithieno[3′,2′:3,4;2″,3″:5,6]benzo[1,2-c][1,2,5]thiadiazole (DTBT) as the third unit, a family
of polymer donors D18, D18–20%Cl, D18–40%Cl, and D18–Cl
are synthesized for OSCs. With appropriate chlorinated monomer proportion,
the terpolymer D18–20%Cl exhibits proper HOMO energy level
and higher packing density compared with that of other control polymers.
Moreover, the D18–20%Cl:Y6 blend films have favorable morphology
with better face-on crystallization and better charge transport. Consequently,
the D18–20%Cl:Y6-based OSCs obtain a top-ranked PCE of 18.28%
with overall improved device parameters compared to the controlled
D18:Y6 or D18-Cl:Y6-based OSCs (17.50% or 17.02%), which represents
the highest PCE for the reported terpolymer-based binary OSCs. Notably,
the D18–20%Cl:Y6-based OSCs exhibit over 17% efficiency in
a wide molecular weight range. These results demonstrate that the
ternary copolymerization of DTBT and two similar moieties is an efficient
approach for achieving efficient terpolymer donors with well batch-to-batch
reproducibility.