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Computational  design of novel multilayer thermoelectric materials with enhanced figure of  merit for waste heat recovery applications
  • AR,
  • Giuseppe Romano
Giuseppe Romano
MIT
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Abstract

The world’s increasing demand for energy and the environmental impact of global climate change due to the combustion of fossil fuels necessitates improvements in the sustainability of power generation. One way to achieve this goal is through the scavenging of waste heat with thermoelectric generators. A variety of applications including; residential heating, automotive propulsion, and industrial processes generate an enormous amount of unused waste heat that could be converted to electricity using thermoelectric (TE) materials. Therefore, designing and developing novel TE materials with greater performance is crucial to increase the sustainability of such energy systems.
The functionality of TE materials depends on their dimensionless figure of merit (ZT), where ZT = (S2σΤ/k) and S, σ, T and k are, respectively, the Seebeck coefficient, electrical conductivity, absolute temperature and thermal conductivity. In order to develop novel TE devices with enhanced ZT with a large temperature difference between the hot side and the cold side, Thin films from recently developed nanostructured crystalline TE (NSCTE) materials with the best performance (high ZT) at high and low temperatures should be chosen for both p-type and n-type segments, respectively. Through all the study, the cold side temperature of the TE models is set to 300 K (room temperature), while the hot side temperature ranges from 800 to 1200 K. We propose that in addition to ligand replacement, the proper interface engineering to promote ZT value should include creation of hetero-structures in the NSCTE thin films.  Therefore, various 2D ligands will be imposed to the interface of NSCTE materials in both p-type and n-type conditions to find out the best compatible interface material for the developed system with maximum enhanced ZT. The presence of such a heterogeneous interface between two NSCTE materials will result in enhancing the performance of the developed TE devices. The principle operation of the interface is enhanced scattering of the acoustic phonons to reduce the k, while increasing the local electron density of states near the Fermi level due to the quantum confinement effect of the NSCTE materials, which gives rise to the enhanced S. Since the developed systems are layered, the adverse effect of the interface on the charge transfer can be minimized, which is the key for acquirement of high-performance novel multilayer thermoelectric materials. 
In the current research, we propose a novel computational materials design approach by combining multiscale methods utilizing density functional theory (DFT), molecular dynamics (MD) and Boltzmann transport equation (BTE) with intelligent data mining and database construction to design novel thermoelectric materials with enhanced functionally for waste heat recovery applications. In our developed multiscale model, DFT calculations will be performed to study all the relevant physical properties to evaluate the figure of merit ZT. MD calculations will be done to investigate phonon dispersion and lattice thermal conductivity. We will modify the motion equation in MD method to study the phono-electron coupling locally (in the interface) and non-locally for the whole system. BTE will be used to calculate the tensors of the Seebeck coefficient S and electrical conductivity σ in the developed TE systems.  Furthermore, the band gap and ionization potentials (IPs) for NSCTE materials will be calculated to understand the band bending at the interfaces. It is important to understand the band bending for both valence and the conduction bands in the interface since it caused energy barriers for holes and electrons at the interface. Low-energy carriers are scattered more than the high-energy carriers over the energy barrier. The energy filtering effect of the holes would improve the Seebeck coefficient. Besides, the minority carrier (electron) blocking effect may also exist, which can improve Seebeck coefficient. Therefore, it is necessary to understand such effects in a fundamental level, which aids to design new high performance TE materials with superior properties.