Synthesis and Characterization of New D-pi-A Organic Photosensitizers for DSSCs

Dye-sensitizer Solar Cells (DSSC) are innovative devices that allow photon-to-electron conversion without using silicon. The aim of this study is to design, synthesize and characterize a small library of new dyes to be used as sensitizers for TiO2 in DSSCs. The efforts have been focused on purely organic compounds and, since most of the organic dyes reported in the literature have a D-?-A architecture, we decided to concentrate on such structures, aiming to improve the anchoring moiety first. The main reaction steps to build a common D-? scaffold and to link new anchoring functions, have been performed through palladium-catalyzed cross-coupling reactions. The most efficient protocols have been assessed comparing different procedures such Ullmann-type and Buchwald-Hartwig reactions to build new carbon-nitrogen bond; Suzuki and Stille coupling for the carbon-carbon bound formation. Further studies concerning the use of specific legands, microwave-assisted heating, and the use of additives have been done to establish the most advantageous setup of reaction with our specific substrates. Such screening have allowed us to prepare the target molecules with new acceptors based on carboxypyridine containing electron-withdrawing substituents. Small test devices have been prepared with those new dyes as sensitizers: good conversion efficiencies and superior chemical and physical stability under DSSC's working condition have been noticed proving the efficiency of the new anchoring systems. An article concerning this work has already been submitted.