Thermoelectric elements (thermogenerators) with organic semiconductors or semimetals, respectively, are presented. To show the feasibility of such elements, in particular organic charge transfer salts and graphite powder as ‘active’ materials were investigated. These active materials were embedded in a PVC blend and screen printed to build a first thick film prototype. It was shown that combinations of active materials with appropriate resistivity and Seebeck coefficient are promising candidates for future thin film thermogenerators on flexible substrates.
The pi-conjugated organic molecules 3,4,9,10-perylene-tetracarboxylic dianhydride, 1,4,5,8-naphthalene-tetracarboxylic dianhydride, and 1,8-naphthalene-dicarboxylic anhydride were investigated via gas phase and bulk ultraviolet photoemission spectroscopy and compared to density functional theory calculations. Values for final state effects such as intermolecular polarization were determined and the differing features in the spectra interpreted as a consequence of interactions in the thin films. Additionally, the highest occupied molecular orbitals of the molecules clearly show distinctive peaks originating from vibrational excitations, leading to results for Franck-Condon factors.
n doping of the molecular organic semiconductor perylene-3,4,9,10-tetracarboxylic–dianhydride (PTCDA) is often achieved by use of alkali metals as dopants. This doping process is commonly performed in two steps. In the first the dopant is evaporated onto the surface of the PTCDA film. As it has been believed that the dopant shows an inhomogeneous diffusion profile through the layer with most of the dopant accumulated in the first few layers, a subsequent annealing step has been performed in order to reach a homogeneous distribution of the dopant in the whole layer. In this paper experimental results concerning chemical composition ((angle resolved) X-ray photoemission spectroscopy, secondary-ion-mass spectrometry, Fourier transform infrared spectroscopy), electronic structure (ultraviolet photoemission spectroscopy, inverse photoemission spectroscopy), as well as electrical properties (conductivity, Seebeck coefficient) are shown before and after doping and before and after annealing. These results suggest that the deposited dopant is redistributed and partially removed during the annealing step. A model for the dopant distribution is suggested.
n -type doping of the molecular organic semiconductor perylene-3,4,9,10-tetracarboxylicdianhydride (PTCDA) by sodium, potassium, and cesium was carried out. The chemical properties of the doping processes were investigated by means of x-ray photoemission and infrared absorption spectroscopy. Simultaneously the evolution of the occupied electronic states around the transport gap was monitored by ultraviolet photoemission spectroscopy. It was found that the doping ratio depends on the ionization energy of the alkali metal, in particular if compared with the highest occupied molecular orbital ionization energy of the formed alkali-PTCDA complex. Additionally, only in the case of cesium doping, an averaged ratio of two alkali metal atoms per PTCDA was found at the surface. In the case of sodium and potassium, averaged surface doping ratios of only 1.3±0.1 alkali metal atoms per PTCDA molecule can be reached. However, in the bulk phase, nearly complete doping can be reached by all three alkali metals.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.