Facile and Cost-Efficient Synthesis of Photovoltaic Polymers via Direct Arylation Coupling

As the high calibre candidate of lightweight and flexible solar cells, polymer solar cells (PSCs) have made tremendous progress in recent years. However, the active photovoltaic materials in PSCs are mainly synthesized by metal-mediated coupling reaction requiring harsh reaction conditions, multiple-step synthesis, and cumbersome purification, which is not cost-efficient and may bring toxicity concerns. It is not favorable to the production of photovoltaic polymers and PSC devices on a large scale, and therefore unsuitable for the PSCs industrialization. Direct arylation coupling reaction via aromatic C—H bonds activation enables the synthesis of conjugated polymers under mild conditions and simultaneously reduces synthetic steps, difficulty, and toxic reaction byproducts. This review provides an overview of the history of preparing representative photovoltaic polymers utilized in PSCs through direct arylation reactions and discusses the activity and selectivity of C—H bonds in typical building blocks under different reaction conditions. Especially, the impact of direct arylation condition on defect formation and photovoltaic performance of the photovoltaic polymers is addressed and compared with conventional Stille coupling methods.