Descripción a Nivel Molecular de Propiedades Estructurales y Electrónicas en Interfases Orgánicas

Resumo

The structural and electronic properties of the organic-organic interface are of vital importance for the efficient operation of OLEDs and OPVs. One of the challenges for the optimization of organic photovoltaic energy is to know the molecular-scale conditions of the interfaces that favour the dissociation of the exciton in the organic- organic interface (donor (D) / acceptor (A)) and that allow a subsequent efficient charge transport to the electrodes. For this reason, it is necessary to use experimental methodologies that allow investigating, on a molecular scale, the degree of involvement of chemical and structural factors in the generation of electrical charge and in the collection processes in the electrodes. This need has motivated the study and investigation of the structural and electronic properties of the organic-metal interface, as well as organic-organic hetero-structures (D / A) at the molecular level. For this, a combined STM / FM-AFM microscope in UHV is used, which allows measuring the local structure with molecular / sub-molecular resolution, as well as XPS or UPS spectroscopies and NEXAFS measurements depending on polarization. With the final objective of providing a description at a molecular scale of the organic-metal and organic-organic interfaces that serves as a guide for the design of new materials based on organic molecular layers and for the possible improvement of the efficiency of devices. More specifically, the research is focused on preparing, growing, characterizing, and modelling organic interfaces, based on organic molecules of interest as the D / A system. Its study on different monocrystalline surfaces such as Au, Ag, Cu, and Ni, allows the influence of the organic-metal interaction, as well as the electronic properties at the local level. In the first part, an introduction is made of the main theoretical concepts and a description of organic materials, STM / FM-AFM, and complementary techniques used. The second part presents the experimental results and/or theoretical calculations in some cases. In Chapter 4, the manifestation of chirality at various levels of the molecular organization is investigated as a product of the self-assembly on Cu (100) of the enantiomers of the diphenylethylenediamine molecule. Next, in chapter 5, the transfer of the chiral organization, structure and distribution of electron density, and the effect of molecular dipoles on the working function for ordered molecular layers of phthalocyanine ClAlPc on surfaces (111) of Au and Cu. In chapter 6, the investigation of ClAlPc (D) molecules is expanded by combining them with fullerenes C60 (A) on Au (111), investigating the D / A type heterojunctions, as the order and molecular orientation can influence, affect adsorption, and the self-organization of the C60 on ClAlPc / Au (111). On the other hand, in Chapter 7 structural properties of the phthalocyanines FAlPc on Au (111) were studied. In Chapter 8, the fluorinated fullerene C60F48 (acceptor used as a p-type dopant in devices) was deposited on metal surfaces (111), and investigated the electronic structure of molecules, the alignment of energy levels at the metal-molecule interface, and the mechanisms that affect the degree of stability of the chemical species on the different surfaces, more (Cu and Ni), or less reactive (Au). In Chapter 9 we investigated the structural and electronic properties (using synchrotron radiation) of the donor molecules octyl benzothiene benzothiophene (BTBT-C8) and dioctyl benzothiene benzothiophene (C8-BTBT-C8) after being deposited on the surface of Au (111). Finally, the organic-organic heterojunction has been studied after incorporating the C60F48 acceptor as a molecular dopant. Finally, chapter 10 presents the general conclusions drawn from the results of chapters 4–9 of this thesis.