ORGANIC AND/OR METALLORGANIC FUNCTIONAL MOLECULES AND THEIR POLYMERS FOR APPLICATIONS IN ELECTRONICS AND PHOTONICS.

Abstract

Organic materials have a tremendous potential to transform the world of circuit, display communication technology and renewable energy in near future. In fact organic materials have attracted much interest as possible inexpensive and flexible alternatives to inorganic devices. The aim of this work was the synthesis and characterization of different classes of organic semiconducting materials for possible applications as active layer in electronic and photonic devices. Several synthetic strategies have been developed and promising classes of p and n-type organic semiconductors have been prepared. As p-type materials, polythiophenes 3-substituted by alkoxyphenilic and alkeneoxyphenilic groups were synthesized by adapting a synthetic methodology previously reported in the literature [44], based on oxidative coupling of thiophene monomers using vanadyl acetylacetonate (VO(acac)2) complex as catalyst. In this way, using a very simple and inexpensive procedure we have obtained regioregular polythiophenes with over 90% HT content. This promising materials were successfully employed as active layers in the field of sensor devices for VOCs detection. Successively, we have developed a new synthetic procedure for obtaining poly[3-(4-alkoxyphenyl)thiophene]s with regioregularity similar to that obtained by McCullough and Rieke methods in the synthesis of poly-3-alkylthiophenes, in order to use this class of materials in a broader field of applications in organic electronics. This novel synthetic methodology, that keeps simplicity and cheapness of the method based on oxidative catalysis using VO(acac)2 complex, allows to prepare poly[3-(4-alkoxyphenyl)thiophene]s by oxidative catalysis using different Cu(II) complexes with very high regioregularity, up to 99% of HT content and represents an interesting alternative to the more expensive classical procedures for the synthesis of poly-3-substituted thiophenes. Remarkable potentialities of highly regioregular poly[3-(4-alkoxyphenyl)thiophene]s have emerged from preliminary FET measurements, that have shown hole mobility up to 1.0*10-4cm2V-1s-1 and a high stability even when device operated in air. For what concerns the developing of new n-type semiconductors, we have synthesized PDI derivatives functionalized at the imide nitrogen with a thiadiazole and triazole groups. Using the new PDI derivatives as active materials in OTFT devices, we have achieved air stable electron mobility up to 1.6*10-2 cm2volt-1sec-1. Finally we have investigated the suitability of one of the synthesized highly regioregular polythiophene, PT8 and one dithiazole derivative of PDI, TDZ-C7 as possible, respectively, donor and acceptor materials in a heterojunction solar cell. Preliminary analysis were carried out through cyclic voltammetry (CV) in combination with UV-Vis optical absorption and photoluminescence emissions. The low bandgap of PT8 (~1.6 eV), its very stable HOMO energy (-5.55 eV) along with a favorable band offset of PT8 and TDZ-C7 and quenching of the photoluminescence of the latter upon mixing with the former, make this couple of materials excellent candidates to assemble photovoltaic cells.