A Conjugated Random Copolymer of Benzodithiophene-Difluorobenzene-Diketopyrrolopyrrole with Full Visible-Light Absorption for Bulk-Heterojunction Solar Cells

Stille coupling polymerization is used to synthesize a new donor-acceptor (D-A) conjugated random copolymer (PBDT-DFB-DPP) that comprises an electron-rich benzodithiophene (BDT) unit in conjugation with electron-deficient 2,5-difluorobenzene (DFB) and diketopyrrolopyrrole (DPP) moieties, which have complementary light-absorption behavior. The thermal, photophysical, and electrochemical properties of the polymer are investigated using thermogravimetric analysis, UV-vis absorption spectroscopy, and cyclic voltammetry. The random copolymer exhibits both broad light absorption and a low-lying highest occupied molecular orbital (HOMO) level, which contribute to enhancement of the short-circuit current density (J(sc)) and open-circuit voltage (V-oc). A bulk-heterojunction polymer solar cell fabricated from PBDT-DFB-DPP and PC60BM exhibits a promising power conversion efficiency (PCE) of 2.50%.