Quinoxaline-based conjugated polymers for polymer solar cells

Bulk heterojunction (BHJ) polymer solar cells (PSCs), as a promising alternative to conventional silicon-based solar cells, have achieved rapid development in recent years. In the BHJ concept, the active layer of the PSC normally consists of a blended film of a conjugated polymer donor and an electron acceptor. To be a conjugated polymer with OPV function, the polymer should have sufficient solubility, a broad absorption spectrum, a high absorption coefficient, and well-matched energy levels with the electron acceptor. With this aim, numerous conjugated polymers have been developed to date. Among them, quinoxaline-based polymers have been shown to have a promising future, reaching a very outstanding power conversion efficiency (PCE) of more than 11%, which shows that they have significant potential in reaching the efficiency limit of commercial applications of polymer solar cells. In this review, we summarize the quinoxaline-based conjugated polymers for efficient polymer solar cells by classifying them in terms of different donors, alkyl and/or aromatic chains, and functional groups, and we also give an overview of their photovoltaic device performances to provide a better understanding of and guidelines for the structure-performance relationship in such quinoxaline-based polymers. We believe that further developments of quinoxaline-based conjugated polymers achieved through the synergy of molecular engineering strategies will increase the photovoltaic performance to levels closer to those required for commercial applications in the near future.