New Random Terpolymers Based on Bis(4,5-didodecylthiophen-2-yl)-[1,2,5]thiadiazolo[3,4-i]dithieno[3,2-a:2',3'-c]phenazine with Variable Absorption Spectrum as Promising Materials for Organic Solar Cells

A series of new random terpolymers was synthesized by copolymerization of one electron-donor alkyl-substituted benzodithiophene unit and two electron-acceptor units, diketopyrrolopyrrole (DPP) and bis(4,5-dodecylthiophen-2-yl)-[1,2,5]thiadiazol[3,4-i]dithieno[3,2-a:2',3'-c]phenazine (DF). The influence of the DPP/DF ratio on the thermal, optoelectronic, and electrochemical properties of the terpolymers was investigated using thermogravimetric analysis, UV-Vis spectroscopy, and cyclic voltammetry. The optical properties of the synthesized terpolymers were controlled by varying the DPP/DF ratio. An increase in the DF mole fraction in the polymer chain caused an increase in absorption intensity in the 300‒600 and 600‒1100 nm ranges, while increasing mole fraction of DPP resulted in stronger absorption in the 600‒900 nm range and lower absorption intensity in the 350‒600 nm range. The terpolymers exhibited broad and intense absorption over the spectral range from 300 to 1100 nm. The results demonstrate that random terpolymers with complementary absorption spectra have a great potential for increasing the photocurrent and efficiency of polymer solar cells.