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

Abstract

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.