Effect of Thienyl Substituted Benzodithiophene and Fluorinated Phenazine in Copolymer for Polymer Solar Cells
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A new conjugated polymers (PBDTT-DT-DoDFPz and PBDTT-DT-DHDFPz), which respectively using Difluorinated Phenazine (DFPz) as an electron-deficient unit and a thienyl substituted benzo[1,2-b:4,5-b']dithiophene (BDTT) as an electron-rich unit, were synthesized by a Stille coupling reaction using palladium catalyst. These polymers could be dissolved in an organic solvent such as chloroform, chlorobenzene (CB), o-dichlorobenzene (o-DCB). These polymers were observed an optical bandgap of 1.62-1.78eV, with highest occupied molecular orbital (HOMO) energy level of -5.29 and -5.37eV. Polymers with branched alkyl side chains had deeper HOMO values than polymers with linear alkyl side chain. All the conjugated polymers showed strong absorption in the range of 500-750nm in film state. As a result, high 2.76% of power conversion efficiency (PCE) was achieved with PBDTT-DT-DHDFPz.