Resumen de Thermal transport and thermoelectricity in organic and inorganic thin films
The increase in energy consumption worldwide has not been complemented by the development of clean energy sources, hindering the adoption of effective measures to mitigate the adverse effects of global warming and the degradation of air quality. The rise of power consumption in the Communication and Information Technologies, ICT, is no exception. However, considering that near 60% of the total energy is lost in the form of waste heat during combustion or equivalent processes, it would be possible to adopt energy harvesting strategies, based on waste heat recovery and improved thermal management, to achieve a more rational use of energy. This solution could benefit a large number of potential applications in the areas of sensing and intelligent monitoring for medical, biomedical or energy efficiency and related applications. Thermoelectric (TE) materials can convert heat into electric energy, opening the possibility to recover this lost energy in an efficient way. The main drawback for the widespread commercialization of TE-based devices for generation and/or sensing comes from their low conversion efficiency that makes this technology not competitive with other alternative energy sources such as solar cells and fuel cells. The efficiency of a TE material is related to the figure of merit, ZT, defined as the ratio of three physical quantities that account for the transport of electrons and phonons, the carriers of electricity and heat respectively. Since ZT=((σxS^2)/k)xT the goal is to decrease the thermal conductivity while simultaneously increasing the Seebeck coefficient (S) and/or the electrical conductivity (σ) to achieve high values of ZT in the adequate temperature range.
In this context, the aim of this thesis is twofold. In a first part, this work is devoted to find and characterize efficient thermoelectric organic and inorganic materials with a good potential for energy harvesting applications. Thereunto, characterization techniques previously implemented in our group as well as new techniques are used. Also, one of these materials is used in a prototype thermoelectric generator. On the second part, a Si-membrane-based microthermoelectric generator (µTEG) is evaluated as photosensor. These measurements show an unexpected enhancement of the Seebeck coefficient produced through the interaction with light. To better evaluate this photothermoelectric effect, a new device is designed, microfabricated, tested and characterized.
