Structures and properties of conjugated Donor-Acceptor copolymers for solar cell applications

With the rapid evolution of photovoltaic polymer materials, power conversion efficiency of polymer solar cells has been markedly improved in recent years, and is now approaching a landmark value of 10 %. This review focuses on Donor-Acceptor (D-A) photovoltaic copolymers. Starting from briefly introducing the D-A concept, the fundamental donor and acceptor units for constructing polymer photovoltaic materials are introduced and classified. By summarizing the structure-property relationships of typical photovoltaic D-A copolymers, the important design rules for such materials are highlighted. Several crucial aspects, including proper combination of D-A units, high planarity of the backbone and proper incorporation of side chains are particularly emphasized. A new D-A architecture, namely main-chain donor and side-chain acceptor is introduced and reviewed. Moreover, the role of the electron-deficient group in fine-tuning energy levels of low-bandgap D-A photovoltaic polymers is discussed.