Dimethyl-2H-benzimidazole based small molecules as donor materials for organic photovoltaics

Utilization of 2,2-dimethyl-2H-benzimidazole has received strong attention as the electron-deficient unit for the generation of electron donor material for organic photovoltaic cells (OPVs). This paper reports the first small organic molecules based on dimethyl-2H-benzimidazole, which can produce intramolecular charge transfer. Two soluble small organic molecules, MMM and OMO, with dimethyl-2H-benzimidazole unit were synthesized by Suzuki coupling reaction with Pd(0)-catalyst. The spectra of MMM and OMO in the solid thin films show absorption bands with maximum peaks at 374, 598 and 373, 588 nm, and the absorption onsets at 678 and 673 nm, corresponding to band gaps of 1.83 and 1.84 eV, respectively. The devices comprising MMM with PC61BM (1:3) showed a VOC of 0.66 V, a JSC of 2.03 mA/cm2, and a fill factor (FF) of 0.27, giving a power-conversion efficiency of 0.37%.