Features of obtaining and properties of thin films organic semiconductors

Abstract

In recent decades, thin films of organic semiconductors (OS), or, as they are also called, organic molecular crystals, have attracted special attention in connection with a number of proposals for their use in functional units of modern electronics, and therefore in modern technological equipment. At the same time, the optical, electrophysical and photoelectric properties of OS are very important, which are determined both by the structure of organic molecules, that is, the starting material, and by the crystal structure of condensates, that is, by the technological conditions of film production. In this regard, this article presents the results of studies of some properties of OS and the technology of obtaining thin films based on them. OS are characterized by weak intermolecular bonds of the Van der Baals type, which causes the low energy of their crystal lattice. In this regard, the electronic structure of individual molecules during the formation of a crystal does not change significantly, and the properties of the crystals almost completely preserve the individual features of the molecules in combination with new properties caused by their collective interaction. This determines the main features of optical and electrophysical properties of OS, their energy structure of neutral and ionized states. In this article, it is experimentally confirmed that the planar structure of atoms of molecular crystals, in particular, linear acenes, and therefore the number of π-electrons responsible for exciton absorption in the visible region of the spectrum determines the position of the edge of their own optical absorption. It was also confirmed that the long-wavelength shift of the optical absorption edge of thin films of phthalocyanines is observed when atoms of heavy elements, for example, lead, are introduced into the molecule. When atoms of lighter elements are introduced into the phthalocyanine molecule, their planarity is not disturbed, and the long-wavelength shift of the edge is much smaller. An explanation of such changes is presented based on the interaction of foreign atoms with the π-electron system of phthalocyanine rings of neighboring molecules. The significant influence of the technological parameters of production, in particular the temperature of the substrate during thermal sputtering, on the crystal structure and optical properties of thin films of linear polyacenes and metallophthalocyanines has been demonstrated and substantiated. The possibility of controlling and presetting the necessary properties of thin-film condensates of molecular crystals is shown.