Síntesis de nuevos sistemas poliheteroaromáticos autoensamblables y estudio de la relación estructura-propiedad en el contexto de la electrónica orgánica

Abstract

Organic Electronics has emerged as a multidisciplinary research area dedicated to the study and development of organic semiconductors, as well as optoelectronic devices fabricated with these materials, with the aim of offering a potential alternative to the traditional technology based on inorganic semiconductors. The use of organic materials for the fabrication of electronic devices provides very attractive properties for the industry, such as lightness and flexibility of the final product at a reduced cost. Within this field it is worth highlighting, the organic field-effect transistors (OFETs), the organic light-emitting diodes (OLEDs) and the organic solar cells (OSCs), among other applications. Although organic semiconductors offer the advantage of tuning the physical and chemical properties of the material by adapting the synthetic methodology, electric charge transport is a feature that still needs optimising. This issue is due to their nature as molecular solids, whose structuration is governed by weak non-covalent interactions, mainly - interactions, which complicate the formation of extended domains with a high degree of order, negatively affecting the displacement of electric charges. Thus, this PhD thesis proposes as objective the synthesis of polyheteroaromatic systems that are able to self-assemble through interactions with higher energy, such as hydrogen bonds, to induce a higher degree of ordering in the solid state. For that purpose, hydrogen bond donor and acceptor sites have been integrated within the -conjugated backbone itself through the condensation of 7-azaindole units with diverse aromatic spacers (benzene, naphthalene, anthracene and pyrene). Therefore, a series of molecules has been synthesised to evaluate the relationship of structural aspects such as isomerism, extension of the -conjugated surface, or the ability to take part in a self-assembly process, with properties such as the crystal packing, the electronic structure and the quality of the hole transport. Chapter 1 makes an introduction to charge transport in organic materials and presents a selection overview of hydrogen-bonded organic semiconductors. Chapter 2 details the synthetic protocols that have been optimised for the preparation of the self-assembled polyheteroaromatic systems and their non-self-assembled analogues, as well as their structural, thermal, optical and electrochemical characterisation, complemented by DFT computational calculations. Chapter 3 discusses the charge transport properties of the synthesised molecules, both from a theoretical and experimental approach, using them as semiconductors for the fabrication of OFETs. Moreover, a study of the effect of self-assembly, or the absence of it, on the performance of thin-film transistors is also carried out by comparing two analogous compounds based on a central anthracene spacer. Chapter 4 shows the results corresponding to the evaluation of the self-assembled molecular materials as hole transporting layers in perovskite solar cells with conventional (n-i-p) or inverted (p-i-n) architecture, as well as in hybrid Pb-Sn perovskite solar cells. Chapter 5 presents the adaptation of the synthetic methodology developed in this Thesis for the preparation of a self-assembled tripodal conjugated molecule with C3h symmetry. This feature makes the objective of this Thesis applicable to the development of two-dimensional materials. Furthermore, the results of surface self-assembly on Au(111) obtained by LEED, STM and computational calculations are discussed. Lastly, the general conclusions drawn from this PhD Thesis are presented