Structural similarity induced improvement in the performance of organic solar cells based on novel terpolymer donors

Terpolymers have been proven to be promising polymer donors for organic solar cells (OSCs). However, the aperiodic sequence distribution caused by random copolymerization dramatically interrupts the orderly stacking of the conjugated main chain. In this work, we reported three terpolymers by introducing Si and Cl functionalized benzodithiophene (BDT-SiCl) into a polymer PM6 matrix with F functionalized benzodithiophene (BDT-2F) by random copolymerization. BDT-SiCl has the same skeleton as BDT-2F, but only differs in functional atoms on the side chain. The structural similarity of the two building blocks not only can minimize the disturbance of the molecular orderly packing caused by random copolymerization, but also can enhance the face-on orientation of the active layer to facilitate charge transport. Moreover, the alkylsilyl and chlorine atom enable the terpolymers to have a lower HOMO level and broadened light absorption compared to PM6. As a result, the terpolymer-based OSCs achieve the best efficiency of 16.22% with a small energy loss of 0.50 eV, yielding overall improved device parameters compared to PM6-based devices. In addition, thanks to the chemical bond linkage, the terpolymer-based device has a higher thermal stability than its corresponding ternary OSC. These results demonstrate that the design concept of structural similarity is a promising strategy to construct terpolymers for high-performance OSCs.