Synthesis and photovoltaic properties of polythiophene incorporating with 3,4-difluorothiophene units

Two polythiophene derivatives using fluorine atoms and hexyl or hexyloxy group as electron-withdrawing and donating substituents have been synthesized. The introduction of fluorine atoms to the polythiophene backbones simultaneously lowers the HOMO and narrows the bandgap, and the stronger electron-donating ability of hexyloxy side chain further reduces the bandgap. As a result, poly[3-hexylthiophene-2,5-diyl-alt-3,4-difluorothiophene] (PHTDFT) shows HOMO and bandgap of -5.31/1.83 eV and poly[3,4-dihexyloxythiophene-2,5-diyl-alt-3,4- difluorothiophene] (PDHOTDFT) shows HOMO and bandgap of -5.14/1.68 eV, both are lower than -4.76/2.02 eV of P3HT. Benefiting from the lower HOMO, PHTDFT:PC ₆₁BM (1:1) polymer solar cells obtain a power conversion efficiency of 1.11% and an impressed open-circuit voltage of 0.79 V under solar illumination AM1.5 (100 mW/cm²). Two new polythiophene derivatives incorporating with 3,4-difluorothiphene units, PHTDFT and PDHOTDFT, show lower HOMO and narrower bandgap than that of P3HT. Benefiting from the lower HOMO, PHTDFT:PC₆₁BM (1:1) polymer solar cells obtain a power conversion efficiency of 1.11% and an impressed open-circuit voltage of 0.79 V under solar illumination AM1.5 (100 mW/cm²).