Conjugated copolymers based on dihexyl-benzimidazole moiety for organic photovoltaics

In this study, we report the synthesis, characterization, and photovoltaic properties of a series of four conjugated polymers based on donor-acceptor (D-A) structure. New polymers, P1, P2, P3 and P4 utilizing a new accepter, dihexyl-2H-benzimidazole, were synthesized using Stille coupling reaction. Even with two bithiophene units in the copolymers to facilitate absorption at the longer wavelength, the incorporation of dihexyl-substituent on 2H-benzimidazole enables the polymers to have good solubility. The spectra of the solid films show absorption bands with maximum peaks at about 442–479 nm and the absorption onsets at 529–575 nm, corresponding to band gaps of 2.16–2.34 eV. The device with P4:PC71BM blend demonstrated an open-circuit voltage (VOC) of 0.59 V, a short-circuit current (JSC) of 6.43 mA/cm2, and a fill factor (FF) of 0.39, leading to the efficiency of 1.46%.