Fused cyclopentadithienothiophene acceptor enables ultrahigh short-circuit current and high efficiency >11% in as-cast organic solar cells

A new method to synthesize an electron-rich building block cyclopentadithienothiophene (9H-thieno-[3,2-b]thieno[2″,3″:4′,5′]thieno[2′,3′:3,4]cyclopenta[1,2-d]thiophene, CDTT) via a facile aromatic extension strategy is reported. By combining CDTT with 1,1-dicyanomethylene-3-indanone endgroups, a promising nonfullerene small molecule acceptor (CDTTIC) is prepared. As-cast, single-junction nonfullerene organic solar cells based on PFBDB-T: CDTTIC blends exhibit very high short-circuit currents up to 26.2 mA cm⁻² in combination with power conversion efficiencies over 11% without any additional processing treatments. The high photocurrent results from the near-infrared absorption of the CDTTIC acceptor and the well-intermixed blend morphology of polymer donor PFBDB-T and CDTTIC. This work demonstrates a useful fused ring extension strategy and promising solar cell results, indicating the great potential of the CDTT derivatives as electron-rich building blocks for constructing high-performance small molecule acceptors in organic solar cells.