Dottorato in SCIENZE CHIMICHE

Titolo della tesi: Synthesis and characterization of novel hybrid perovskites featuring quaternary organoammonium cations with extended conjugation

The last decade has seen an unprecedented interest in hybrid metal halide perovskites semiconductors, as active layers in photovoltaic cells, with extraordinarily high efficiency values achieved, and for various different optoelectronic applications, especially light emission and radiation detection. In fact, these materials have the advantage of being synthesized from affordable precursors by solution techniques, and of allowing a fine tuning of their photophysical properties through the modification of their composition. Regretfully, their utilization on a large scale is still hindered by their poor environmental stability, owed to the ammonium cations contained in them, which undergo hydrolysis reactions in the presence of water; for this reason, the main goal of the current research in the field of hybrid perovskites is represented by the improvement of their tolerance to moisture and other environmental agents (such as high temperature and O2). The aim of this work was therefore the study of the possibility to enhance perovskite stability and performances, through the introduction of novel organic cations featuring the following characteristics: an extendedly conjugated structure, in order to modulate the optoelectronic properties of the materials, and the absence of hydrolysable protons, to avoid decomposition in the presence of moisture. In particular, the synthesis and characterization of two novel water-insensitive and thermally stable hybrid metal halide perovskites, containing 4,4′-(anthracene-9,10-diylbis(ethyne-2,1-diyl))bis(1-methyl-1-pyridinium), (C30H22N2)2+ cation, is described in Chapters 3 and 4. The two materials, both of which showed intense photoluminescence, were prepared using different metals, lead in the first case and bismuth in the second, with the aim of exploring the possibility of replacing a toxic element such as lead (which is however the most frequently used metal in hybrid perovskites) with a safer alternative. Moreover, the synthesis of a series of additional environmentally stable lead-based and bismuth-based hybrid materials, sharing the presence of quaternary conjugated bipyridinium cations is described in Chapter 5, together with a preliminary evaluation of their potentialities for applications.