A small- molecule acceptor incorporating a silicon bridging atom for efficient nonfullerene polymer solar cells

Recently, there have been rapid advances in polymer solar cells (PSCs) based on nonfullerene small-molecule acceptors (n-SMAs) due to their outstanding properties. Silicon, which is a member of group 14 in the periodic table, may endow small-molecule acceptors with unique properties, especially when it is incorporated into conjugated backbones. In this work, a narrow band gap n-SMA based on a dithienosilole (DTS) unit incorporating silicon bridging atom, named Si4TIC-F, was designed and synthesized. Si4TIC-F has a rigid, planar conjugated backbone, benefiting intermolecular stacking and charge transport. Pairing Si4TIC-F with a wide band gap copolymer, poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b]-dithiophene-alt-N-(2-hexyldecyl)-55-bis[3-(decylthio)thiophene-2-yl]-22-bithiophene-33-dicarboximide] (PBTIBDTT), achieved a power conversion efficiency (PCE) of 10.2%. The PCE is much better than those of other systems with DTS-based acceptors. Our results demonstrate the potential of the classical DTS unit in constructing new n-SMAs to realize high-performance nonfullerene PSCs, which will help advance the development of PSCs.