Synthesis of a conjugated copolymer with benzodithiophene and benzimidazole units

Abstract

new accepter unit, dimethyl-2H-benzimidazole, was prepared and utilized for the synthesis of conjugated polymers containing an electron donor-acceptor pair for organic photovoltaics (OPVs). A dimethyl-2H-benzimidazole unit was designed to replace the benzothiadiazole (BT) unit of PCDTBT. An advantage of dimethyl-2H-benzimidazole compared with the BT moiety of PCDTBT is that the solubility of the polymer is improved while the 1,2-quinoid form is maintained to lead the coplanarity of the backbone. New semiconducting copolymers with dialkoxybenzo[1,2-b:3,4-b'] dithiophene as the electron-rich unit and 2,2-dimethyl-4,7-di(2-thienyl)-2H-benzimidazole as the electron-deficient unit were synthesized by Pd(0)-catalyzed Stille coupling polymerization. The resulting P2:PC71BM device had a open circuit voltage (V-OC) value of 0.65V, a short circuit current density (J(SC)) value of 1.86mAcm(-2) and a FF value of 0.39, with a final power conversion efficiency (PCE) value of 0.47%.