How to design low bandgap polymers for highly efficient organic solar cells

Organic photovoltaic cells are promising in terms of their light weight, mechanically flexibility, ease of processing and low cost. Establishing a predictive understanding between the chemical structures and physical properties of polymers is still challenging, and continuous effort is needed to progress toward full commercialization. In this review, recent progress in polymer/fullerene systems is highlighted and four synthetic principles are summarized to engineer the bandgap and tune the energy levels and the solubility of the targeted polymers.