DESIGN AND SYNTHESIS OF NEW COMPOUNDS FOR PHOTOVOLTAICS APPLICATIONS AND PHOTOCATALYTIC H2 PRODUCTION

The phenomenon of global warming, coupled with the progressive depletion of fossil fuels reserves, demand their rapid replacement with renewable energy sources. Among them, solar energy appears very appealing since it is abundant, ubiquitous and practically inexhaustible. Furthermore, solar energy can be exploited in several different ways, since it can be converted both to electricity and fuels. The most promising method for solar electricity production is based on photovoltaic cells and related devices. Among new-generation photovoltaic devices, dye-sensitized solar cells (DSSC) emerged for their simple manufacturing and peculiar working mechanism, making them particularly suitable for building integration and indoor electricity generation; perovskite solar cells (PSCs), on the other hand, currently attract great attention due to their high efficiencies, which almost rival those of traditional silicon-based modules. Concerning the field of fuels, H2 seems to be the perfect candidate to replace fossil fuels since it is carbonfree, can be produced from water and has a high energy content. Contrary to traditional electrolysis, photocatalytic H2 production can be considered a promising and cheap alternative to produce H2 in a green and sustainable way. The work presented in this Ph. D. thesis was focused on the development of new light responsive materials that can be employed in all the fields described above. The first part of the work deals with the modification of well-known organic DSSC sensitizers featuring a donor-π-acceptor structure. In particular, we modified their acceptor moiety by introducing one or more sulfur atoms. The presence of a sulfur atom in the anchoring group induced a red-shift and a broadening of the absorption spectrum compared to typical carboxylic dyes, but did not affect the charge injection capability of the sensitizers, resulting in DSSCs of similar efficiency. The second part of the thesis analyzes the effect of alkaline cation size on the efficiency of quasi solid-state DSSCs built with a commercial organic dye (D35). For this purpose, five different gel electrolytes containing I2 and five different alkaline iodides (LiI, NaI, KI, RbI, CsI) were prepared and characterized. Incorporation of the different alkaline ions induced changes in the conductivity of the gels, altering the performance of the corresponding DSSCs in function of the charge density of the cations. In the third part, the synthesis and characterization of two new Hole Transporting Materials (HTMs) for PSCs are described. A common pillar[5]arene scaffold was functionalized with two different triarylamine fragments, in order to obtain two innovative multi-branched HTMs. The materials were fully characterized and a preliminary screening of the properties of the corresponding solar cells was carried out, highlighting the crucial role of additives to boost their performances. Finally, the last part of this thesis is focused on the synthesis of three new D-π-A organic dyes, bearing a dithienosilole core, suitable for photocatalytic H2 production by adsorption on a nanostructured Pt/TiO2 catalyst. Structure-activity relationships for such dyes were investigated by evaluating the effect of the introduction of alkyl chains on different positions of their scaffold, which were found to influence several properties such as solubility, aggregation, shielding and wettability of the semiconductor surface.