Design of planar-zigzag semiconducting polymers to control chain orientation and electronic structure for organic photovoltaics

A series of π-conjugated copolymers containing V-shaped electron-deficient units of triphenyleno[1,2- c :7,8- c ′]bis([1,2,5]thiadiazole) (TPTz) or its non-fused precursor were synthesized. Both the ring fusion in TPTz and the appropriate spacer units between TPTz and the donor unit were important for allowing the polymers to adopt a planar-zigzag shape as the stable chain conformation. The planar-zigzag shape of the polymers strongly affected their anisotropic electronic and electrical properties in thin films, and in particular, the face-on orientation increased not only the absorption coefficients but also the charge carrier generation and collection efficiency, resulting in improved photovoltaic performance in mixed bulk heterojunction films with an electron acceptor. The planar-zigzag shape of polymers leads to a face-on orientation of the main chains in thin films which improves the photovoltaic performance through better absorption coefficients, charge carrier generation, and collection efficiency.