Design and synthesis of BODIPY sensitizers with long alkyl chains tethered to N-carbazole and their application for dye sensitized solar cells

Abstract

In this study, three boron dipyrromethenes (BODIPY) dyes with extended conjugation and electron donating carbazole groups with different alkyl chain lengths tethered to N-carbazole were synthesized and characterized for dye-sensitized solar cells. The goal was to study the effect of different alkyl chain lengths on dye aggregation at TiO2 surface. The proposed molecular strategy resulted in BODIPY dyes which showed interesting electronic absorption and fluorescence properties. It was observed that intramolecular energy transfer decreases with the increase in alkyl chain length possibly due to induced changes in molecular geometry caused by long alkyl chains. Additionally, interface analysis by impedance spectroscopy in comparison to N719 sensitized TiO2 solar cell showed significant charge transport related losses (Nyquist plot) most likely due to impedance resulted from aggregated BODIPY dye on TiO2 surface. Femtosecond transient absorption studies showed the loss of excited electrons by recombination with oxidized ground state of the sensitizers.