The effect of molecular structure and ultrafast electron injection dynamics on the efficiency of BODIPY sensitized solar cells

Abstract

In an attempt to investigate the effect of charge transfer dynamics on the photovoltaic performance of the dye-sensitized solar cells (DSSCs), a new series of 4,4-difluoro-3a,4a-diaza-s-indacene (BODIPY) compounds were designed and sensitized. Charge transfer dynamics of the studied compounds were investigated by using femtosecond transient absorption (TA) spectroscopy technique. TA spectroscopy results revealed that excited state lifetime of the sensitized dyes can be controlled by altering the position of the anchoring group as well as the conjugation length of the studied compounds. Photovoltaic performances of the DSSCs produced with the sensitized dyes were evaluated by using incident photon to current efficiency (IPCE) spectra as well as IV measurements. It was found that the dye with longer conjugation length showed efficient electron injection to the conduction band of the semiconductor (TiO2) depending on the anchoring group position. In addition to that, the adsorption of the sensitizer on the TiO2 was affected by the position of OH moieties. Therefore, the results of IPCE and J-V measurements suggest that, in order to improve the photovoltaic performance, the anchoring group should be bound to the positions which do not prevent the molecular rotation. This work could be useful for developing new strategies towards molecular engineering for DSSC applications.