Synthesis and Solar Cell Application of New Alternating Donor–Acceptor Copolymers Based on Variable Units of Fluorene, Thiophene, and Phenylene

A new series of donor–acceptor copolymers were synthesized via the Witting route and applied as an active layer in organic thin-films solar cells. These copolymers are composed of fluorene–thiophene and phenylene–thiophene units. The ratio between those was systematically varied, and copolymers containing 0%, 50%, and 75% of phenylene–thiophene were characterized and evaluated when used in photovoltaic devices. The copolymers' composition, photophysical, electrical, and morphological properties are addressed and correlated with device performance. The 50% copolymer ratio was found to be the best copolymer of the series, yielding a power conversion efficiency (PCE) under air mass (AM) 1.5 conditions of 2.4% in the bilayer heterojunction with the C₆₀ molecule. Aiming at flexible electronics applications, solutions based on the heterojunction of this copolymer with PCBM (6,6-phenyl-C₆₁-butyric acid methyl ester) were also successfully deposited using an inkjet printing method and used as an active layer in solar cells