Isoindigo derivatives for application in p-type dye sensitized solar cells

In this study, we have investigated for the first time the use of isoindigo derivatives as sensitizers in NiO-based dye-sensitized solar cells (DSSCs). For this purpose, two indigo sensitizers were prepared and their electronic properties were characterized by UV/visible spectroscopy, cyclic voltammetry and time-dependent density functional theory (TD-DFT). The first dye contains a N, N-di(4-benzoic acid) phenylamine moiety acting as anchoring/donor group, and the isoindigo acting as the acceptor, while the second compound is a dyad which is based on the same structure, but is additionally functionalized with a naphthalene imide unit, acting as a secondary electron acceptor. The electronic properties were also modeled by TD-DFT quantum chemistry calculations and they revealed that a charge transfer band is present between the trisarylamine donor part and the isoindigo moiety. The photovoltaic performances of these new dyes were evaluated in NiO-based DSSCs with both iodide/triiodide and cobalt electrolytes. It turned out that they perform well since the photocurrent was generated up to the wavelength of 700 nm. Altogether, these results underscore the viability of isoindigo dyes for p-DSSCs.