Tailoring the second acceptor unit in easily synthesized ternary copolymers toward efficient non-fullerene polymer solar cells

A series of D-A 1 -D-A 2 structured copolymers were synthesized by combining the simplest donor unit of thiophene (Th) and dual easily available acceptor units of alkoxylated benzoxadiazole (ROBO) and quinoxaline (ROQx). Short alkyl side chains were distributed over the dual acceptor units to dilute steric hindrance while guaranteeing solution processing of the polymers. The strong acceptor properties of benzoxadiazole (BO) could enhance the intramolecular charge transfer (ICT) interactions, while the weak acceptor of quinoxaline (Qx) may be used to strengthen π-π interactions through the favorable quinoidal structure form. Fixing Th and ROBO units, the effects of fluorination of the Qx unit were investigated. PSCs based on 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]- s -indaceno[1,2-b:5,6-b′]dithiophene (ITIC) and PTBOQ-F exhibited a superior PCE of 5.84% due to the favorable hole mobility and blend morphology. In comparison, the separated D-A 1 and D-A 2 controls of PTBOQ-F afforded significantly lower PCEs (<1.45%). These results indicate that our approach is a feasible way to obtaining cost-effective polymers by screening the easily accessible moieties in a proper manner of dual acceptor units.