We report that we can enhance the performance of polymer photovoltaics by introducing materials with dipoles at the donor–acceptor interface of the polymer solar cells. We use a zwitterionic conjugated polyelectrolyte (ZCPE) as an interfacial layer in a model bi-layer system consisting of donor and acceptor polymers. We find an increase in short-circuit current and fill factor when a 2 nm thin layer of ZCPE is introduced between donor and acceptor polymers. Absorption of light in the ZCPE interlayer contributes to the photocurrent, and, as revealed by time-resolved pump–push optical spectroscopy, the interlayer reduces the probability of electron–hole recombination at the donor–acceptor interface.