Green organic dyes for DSSC application based on D - A - pi - A design bearing Indigo structure

Although dyes for DSSC capable of providing relatively high efficiencies have already been obtained and the path for improving the dye stability has already been undertaken, there are other issues which have been less investigated and need to be addressed. The new challenge in the field of building integrated photovoltaics is to complete the palette of colorations available for DSSCs. The development of libraries of dyes characterized not only by long term stability and considerable high efficiency but also by a wide choice of colors, would make the exploitation of DSSCs much more appealing from an architectural point of view. In this work, the preparation of near-IR absorbing green dyes is reported. The obtained compounds were spectroscopically and electrochemically characterized and the innovative dyes were employed to sensitize DSSC devices to evaluate their photo-electronic properties. To design dyes possessing the desired coloration, we referred to D-A-?-A structures. With such design, a relatively small energy gap between the frontiers orbitals is predicted resulting in near-IR absorption. The dyes reported in this work are characterized by Indigo internal acceptor. The peculiar blue coloration of Indigo structures is due to the cross-conjugated system of two electron-donating functio ns and two acceptors (the amines and the carbonyl functions respectively) known as H-Chromophore left.