Noncovalent Conformational Locks Enabling Efficient Nonfullerene Acceptors

A simple synthesis of highly planar extended pi-electron molecules is of particular interest for the development of efficient nonfullerene acceptors in organic solar cells with high light absorption and high mobility. Herein, two small-molecule acceptors (MPU7 and MPU8) with a diketopyrrolopyrrole core connected to CPTCN end-capping groups (A(2)) via thienylethynylselenophene (MPU7) or thienylethynylthiophene (MPU8) linkers are conceived and synthesized. Planarity ofthe conjugated skeleton is achieved in both molecules, thanks to the existence of four (Se center dot center dot center dot O or S center dot center dot center dot O) noncovalent, through-space intramolecular interactions. Both nonfullerene small-molecule acceptors show broad absorption in the visible and near-infrared region (up to 930 nm). As a result, the binary solar cells constructed together with a polymer donor (P) display power conversion efficiencies as high as 14.12%. Devices built with MPU7 (containing the selenophene) show better film morphology, electron mobility, and higher efficiency than those containing thiophene (MPU8).