High‐Performance All‐Small‐Molecule Solar Cells Based on a New Type of Small Molecule Acceptors with Chlorinated End Groups

While a wide variety of nonfullerene acceptors are developed and perform well in combination with polymer donors, only a few nonfullerene acceptors can work well with small molecule donors. Here, all‐small‐molecule solar cells with high performance enabled by a new type of small molecule acceptors (F‐0Cl, F‐1Cl, and F‐2Cl), which contain linear alkyl side chains and end groups substituted with various number of chlorine atoms, are reported. End group chlorination leads to redshifted absorption, enhanced crystallinity, and high electron mobility. These properties make them competitive as electron acceptors for all‐small‐molecule solar devices. When combined with two popular small molecule donors DRTB‐T and DRCN5T, these nonfullerene acceptors offer power conversion efficiencies up to 10.76 and 9.89%, which are among the top efficiencies reported in all‐small‐molecule solar cells and indicate the great potential of all‐small‐molecule solar devices. All‐small‐molecule organic solar cells employing three nonfullerene acceptors (F‐0Cl, F‐1Cl, and F‐2Cl) are investigated. End group chlorination leads to redshifted absorption, enhanced crystallinity, and high electron mobility. F‐2Cl with highest crystallinity gives the best device performances with power conversion efficiency of 9.89 and 10.76%, respectively, when small molecule DRCN5T and DRTB‐T are used as donors.