Saddle‐Shaped Third Component with Out‐of‐Plane Electrostatic Dipole for Realizing High‐Performance Photovoltaic Donor Terpolymers

Terpolymer fabrication is an effective methodology for molecular engineering and generating high‐performance organic photovoltaic materials to construct highly efficient polymer solar cells. Modification of the polymer PM6 by incorporating a third component resulting in the formation of a ternary copolymer is reported to outperform PM6 in achieving enhanced device performances. However, one of the major challenges in constructing high‐performance terpolymers is to counter the molecular disorder caused by the backbone entropy induced by the third moiety. In this work, double B←N bridged bipyridine (BNBP) is used as the third component, which possesses a strong out‐of‐plane electrostatic dipole owing to the saddle‐shaped B←N fused ring structure. The out‐of‐plane dipole moment introduced in the modified PM6 terpolymer can be used as a means for tuning and optimizing the nanostructures of the blended films. The prepared PM6‐BNBP‐4 blend polymer with 4% of the benzodithiophene dione monomers replaced by BNBP results in excellent power conversion efficiency of 19.13%. This work demonstrates that the out‐of‐plane electrostatic dipole moment in saddle‐shaped molecules is valuable for achieving high‐performance organic photovoltaic donor materials. PM6‐based terpolymers containing a saddle‐shaped group with a double B←N bridged bipyridine (BNBP) as the third component designed for fabrication of polymer solar cells feature strong out‐of‐plane dipole for optimizing blend morphology and improving the photovoltaic performances, thus achieving 19.13% efficiency.