Achieving high performance organic solar cells with a closer π–π distance in branched alkyl-chain acceptors

Abstract

Side-chain functional groups have been shown to not only ensure solubility but also influence molecular packing behavior, and side-chain modification is an important strategy in the optimization of photovoltaic performance. Instead of focusing on the size of the alkyl side chains, we have investigated the influence of side-chain configurations on the properties of acceptors and organic solar cells (OSCs). Two acceptor molecules, BTIC-TCl-b and BTIC-TCl-l were designed by changing the linear configuration of alkyl chain substituents on thiophene rings to a branched structure. The results show that the branched configuration of the side-chain can significantly improve the planarity and reduce the π⋯π distances, leading to a more compact 3D-network structure. With the polymer donor PBDB-TF, an outstanding power conversion efficiency (PCE) of 16.17% was achieved by BTIC-TCl-b, which is significantly higher than that found with BTIC-TCl-l. Our study offers new insights for side-chain modification, regulation of the aggregation state, and optimization of photovoltaic performance.