Panchromatic cross-substituted squaraines for dye-sensitized solar cell applications

Much attention has recently been devoted to the design and synthesis of vis–NIR-absorbing chromophores that are suitable for use as photosensitizers in dye-sensitized solar cells (DSSCs). Amongst the different classes of chromophores that have been proposed for this application so far, squaraine dyes have been considered because of their strong intrinsic absorption in the 600–800 nm region and their high thermal and chemical stabilities. The aim of the present work is the exploitation of a design strategy only scantly reported in the literature,[6] and never employed in the context of solar cells: the functionalization of the squaraine core with an electron-withdrawing conjugated residue enabling the appearance of a second, high-energy band in the absorption spectrum. Experimental details for the squaraine syntheses, complete UV-Vis-Fluorescence characterization, technical details for the Cyclic Voltammetry measurements, absorption spectra on TiO2 and technical details for the Dye Sensitized solar cells preparation and measurements are reported. It was demonstrated that functionalization of the squarylium core of squaraines with an electron-withdrawing substituent is an efficient strategy for the preparation of panchromatic sensitizers endowed with a sizeable photonto-electron conversion over the whole visible region. These results should open the way for a new class of squaraine dyes that have high conversion efficiencies.