Efficient wide-band-gap copolymer donors for organic solar cells with perpendicularly placed benzodithiophene units

The working horses for the drastically improved power conversion efficiency (PCE) of organic solar cells (OSCs) were the small-band-gap molecular non-fullerene acceptors. This development not only removed the low performance obstacle for OSCs but also raised needs for wide-band-gap polymers for donor/acceptor mix with complimentary absorptions. Benzodithiophene (BDT) is one of the mostly used unit for constructing donor polymers. Here, we introduced one type of donor polymer with two BDT units placed perpendicularly. This exploration is aimed to reduce the complexity of molecule design, potentially to reduce the cost of donor materials. We also explored the halogenation of BDT side group to optimize the performances of the copolymers. The chlorinated donor polymer PvBDT-Cl delivered a decent PCE of 8.23% with Y6-T. This work explored the possibility of using only BDT unit to construct high performance donor polymers, which is a crucial insight for future low-cost donor polymer design.