The molecular orientations of conjugated materials on the substrate mainly include edge-on, face-on, and end-on. Edge-on and face-on orientations have been widely observed, while end-on orientation has been rarely reported. Since in organic solar cells (OSCs) charge transport is along the vertical direction, end-on orientation with conjugated backbones perpendicular to the substrate is recognized as the ideal microstructure for OSCs. In this work, we for the first time obtained the preferential end-on orientation in a conjugated molecular dyad that contains a conjugated backbone as donor and perylene bisimide side units as acceptor. This was realized by introducing a fused-ring structure to replace linear terthiophenes with conjugated backbones, yielding F-MDPBI and L-MDPBI respectively. Surprisingly, a shifting trend of the molecular orientation from dominating edge-on in L-MDPBI to preferential end-on in F-MDPBI was observed. As a consequence, vertical charge carrier mobilities in F-MDPBI are one order of magnitude higher than those with preferential edge-on orientation, so single-component OSCs based on this molecular dyad as a single photoactive layer provided a power conversion efficiency of 4.89% compared to 1.70% based on L-MDPBI with preferential edge-on orientation.
Bibliographical noteKAUST Repository Item: Exported on 2022-10-17
Acknowledgements: We thank Dr. Bo Guan and Dr. Jiling Yue from the Institute of Chemistry, CAS for cryo-TEM measurement. We also thank Prof. Wei Ma at Xi'an Jiaotong University and Jianqi Zhang at National Center for Nanoscience and Technology, CAS for GIWAXS measurements. This study is supported by jointly supported by the Beijing Natural Science Foundation (JQ210065) and NSFC (52073016 and 92163128) of China. This work was further supported by the Fundamental Research Funds for the Central Universities (buctrc201828 and XK1802-2), the opening Foundation of State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology (oic-202201006), Jiangxi Provincial Department of Science and Technology (No. 20202ACBL213004, 20212BCJ23035, jxsq2019102004, and 20203BBE53062), and Jiangxi Academy of Sciences (2021YSBG22034, 2021YSBG22033, and 2020-YZD-3). A.C.Y.L. acknowledges support from the Australian Research Council (FT180100594).