Development of quinoxaline based polymers for photovoltaic applications

Polymer solar cells (PSCs) with a bulk heterojunction (BHJ) structure, i.e. a blend of a p-type conjugated polymer with an n-type semiconductor acceptor, have made rapid progress over the past decade. In comparison with inorganic semiconductor solar cells, PSCs have the advantages of low cost, light weight, solution processability and good mechanical flexibility. In the last few years, various classes of electron-donating polymers have been reported for PSCs. Among them, quinoxaline (Qx) and its derivatives have been widely used as building blocks for optoelectronic applications because they can be easily modified by varying the side chains, such as alkyl chains, conjugated aromatic rings, functional groups, etc. Recently, a power conversion efficiency (PCE) of over 11% was achieved for PSCs with Qx-based polymers. This PCE is among the best for PSCs, and it suggests that Qx-based polymers have great potential for highly efficient PSCs. In this article, we review the recent advances in the design and synthesis of such Qx-based conjugated polymers for photovoltaic applications. Particular attention is paid to the chemical structures of the polymers including flexible chains, conjugated side chains, functional groups, Qx derivatives and the effect of the molecular structure on device performance parameters. We believe that further development of Qx-based polymers will lead to a PCE >12% in the near future.