New monomers, polymers, and blends of polymers with an electron acceptor are provided, e.g., for use in a photovoltaic device. The electron acceptor can be a fullerene derivative and the polymer can comprise monomer units according to the formula: wherein L′ is L-C(O)O-J, L-C(O)NR′-J, L-OCO-J′, L-NR′CO-J′, L-SCO-J′, L-O-J, L-S-J, L-Se-J, L-NR′-J or L-CN; L is a linear or branched alkylene group having from 1 to 10 carbon atoms; J is a hydrogen atom or a linear or branched alkyl group having from 1 to 4 carbon atoms; J′ is a group having from 1 to 10 carbon atoms, being saturated or unsaturated, linear or branched, optionally comprising a phenyl unit; and R′ is a hydrogen atom or a linear or branched alkyl group having from 1 to 4 carbon atoms.