A heptacyclic carbon-oxygen-bridged ladder-type building block for A-D-A acceptorsElectronic supplementary information (ESI) available: Material preparation and characterization, solar cell fabrication and measurements. CCDC 1837067. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c8qm00285a

A heptacyclic carbon-oxygen-bridged ladder-type unit, CO i 7, was designed. Two corresponding nonfullerene acceptors, CO i 7IC and CO i 7DFIC, were developed. The single crystal structure of CO i 7IC indicates an S-shaped backbone and a packing via π-π interaction of the end groups. PTB7-Th:CO i 7DFIC solar cells gave a power conversion efficiency of 8.32%, with a decent fill factor of 71.9%. A-D-A acceptors based on a heptacyclic carbon-oxygen-bridged ladder-type unit, CO i 7, can give a high fill factor in organic solar cells.