Small-molecule acceptors based on 4H-cyclopenta[1,2-b:5,4-b′]dithiophene units with near-infrared absorption for nonfullerene polymer solar cells

Abstract Two small-molecule acceptors 1CIC and 2CIC based on 4H-cyclopenta[1,2-b:5,4-b′]dithiophene units and 1,1-dicyanomethylene-3-indanone were developed. Compared with 1CIC, 2CIC possesses red-shift absorption, higher HOMO and LUMO energy levels, and higher electron mobility. Nonfullerene polymer solar cells based on PTB7-Th:2CIC gave a power conversion efficiency (PCE) of 3.53%, with an open-circuit voltage (Voc) of 0.75 V, a short-circuit current (Jsc) of 10.97 mA/cm2. As contrast, PTB7-Th:1CIC cell gave a PCE of 0.26%. Our results indicated that the absorption spectra of small-molecule acceptors containing indaceno[1,2-b:5,6-b′]dithiophene (IDT) core can be efficiently extended to near-infrared region by replacing the aromatic benzene ring of with 2,2′-bithiophene.