Efficiency as a performance metric for material optimization in thermoelectric generators

Ponnusamy, Prasanna; Kamila, Hasbuna; Müller, Eckhard; Boor, Johannes de

doi:10.1088/2515-7655/ac293e

Cited by 6 publications

(6 citation statements)

References 40 publications

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“…Indeed, supposing that the whole leg's Seebeck coefficient changed from −90 µV/K to −110 µV/K (instead of only the areas close to the contacts), it can be deducted, using the Pisarenko plot in Figure S7 in SI, that the carrier concentration would change from n = 3.1 × 10 26 m −3 to n = 2.2 × 10 26 m −3 . It is known that for many material systems, including Mg 2 (Si,Sn) solid solutions, the zT, and therefore the efficiency, are not so sensitive to such a change in carrier concentration, as its peak extends on a broad n range [48].…”

Section: Discussionmentioning

confidence: 99%

Overcoming Asymmetric Contact Resistances in Al-Contacted Mg2(Si,Sn) Thermoelectric Legs

et al. 2021

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Thermoelectric generators are a reliable and environmentally friendly source of electrical energy. A crucial step for their development is the maximization of their efficiency. The efficiency of a TEG is inversely related to its electrical contact resistance, which it is therefore essential to minimize. In this paper, we investigate the contacting of an Al electrode on Mg2(Si,Sn) thermoelectric material and find that samples can show highly asymmetric electrical contact resistivities on both sides of a leg (e.g., 10 µΩ·cm2 and 200 µΩ·cm2). Differential contacting experiments allow one to identify the oxide layer on the Al foil as well as the dicing of the pellets into legs are identified as the main origins of this behavior. In order to avoid any oxidation of the foil, a thin layer of Zn is sputtered after etching the Al surface; this method proves itself effective in keeping the contact resistivities of both interfaces equally low (<10 µΩ·cm2) after dicing. A slight gradient is observed in the n-type leg’s Seebeck coefficient after the contacting with the Zn-coated electrode and the role of Zn in this change is confirmed by comparing the experimental results to hybrid-density functional calculations of Zn point defects.

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Section: Discussionmentioning

confidence: 99%

Overcoming Asymmetric Contact Resistances in Al-Contacted Mg2(Si,Sn) Thermoelectric Legs

et al. 2021

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“…Electrode‐induced defects with formation energies comparable to that of the relevant dopant defect will lead to comparable defect densities, but defects that reduce the carrier concentration (compensating defects) will diminish the TE performance more than defects that increase it (additive defects) as zT ( n ) and efficiency η( n ) reduce more rapidly toward lower majority carrier concentrations. [ 28 ] Thus, the most detrimental are defects with formation energies lower than the relevant dopant defect, with q ≤ −1 at E F = E CBM for n‐type and q ≥ +1 at E F = E VBM for p‐type. For this reason, the defect formation energies shown in Figure 1 are ordered according to their charge transition level from 0 (neutral defect) to −1 (electron compensating defect) in Figure 1a and 0 to +1 (hole compensating defect) in Figure 1b.…”

Section: Resultsmentioning

confidence: 99%

High‐Performance Thermoelectric Devices Made Faster: Interface Design from First Principles Calculations

Ayachi,

Park,

Ryu

et al. 2023

Advanced Physics Research

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The enormous progress achieved with high‐performance thermoelectric materials has yet to be implemented in high‐performance devices. The bottleneck for this is the material‐specific design of the interface between the thermoelectric material and the electrical connections, particularly identifying suitable contacting electrodes. This has mainly been empirical, slowing down device maturation due to the vast experimental space. To overcome this, an electrode pre‐selection method based on first‐principles electronic structure calculations of charged defect formation energies is established in this work for the first time. Such method allows to predict thermoelectric leg degradation due to impurity diffusion from the electrode into the thermoelectric material and formation of charge carrier traps, causing a majority carrier compensation and performance deterioration. To demonstrate the feasibility of this approach, the charged point defect formation energies of relevant metal electrodes with Mg2(Si,Sn) are calculated. Five hundred ten defect configurations are investigated, and the interplay between intentional doping and electrode‐induced point defects is predicted. These predictions are compared with Seebeck microprobe measurements of local carrier concentrations near the Mg2(Si,Sn)‐electrode interface and a good match is obtained. This confirms the feasibility of electrode screening based on defect formation energy calculations, which narrows down the number of potential electrodes and accelerates device development.

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“…Rather, the averaged figure of merit is a better measure of efficiency [77]. Appropriate averages [78] as well as efficiency calculations considering the temperature dependence of the thermoelectric properties [79,80] can be readily obtained using the model introduced here. Overall, the experimental data is captured well by the 2PB model.…”

Section: Discussionmentioning

confidence: 99%

Developing a two-parabolic band model for thermoelectric transport modelling using Mg₂Sn as an example

2022

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Thermoelectrics is a field driven by material research aimed at increasing the thermal to electrical conversion efficiency of thermoelectric (TE) materials. Material optimisation is necessary to achieve a high figure of merit (zT) and in turn a high conversion efficiency. Experimental efforts are guided by the theoretical predictions of the optimum carrier concentration for which generally the Single Parabolic Band (SPB) model is used which considers the contribution to electronic transport only from the majority carriers’ band. However, most TE materials reach peak performance (maximum zT) close to their maximum application temperature and when minority carrier effects become relevant. Therefore, single band modelling is insufficient to model the behaviour of TE materials in their most practically relevant temperature range. Inclusion of minority effects requires addition of the minority carrier band and necessitates the use of a two-band model – the simplest and, for most cases, sufficient improvement. In this study, we present a systematic methodology for developing a two-band model using one valence and one conduction band for any TE material. The method utilises the SPB model and a simple cost function-based analysis to extract material parameters like density of states masses, band gap, deformation potential constant etc., based on easily available experimental data. This simple and powerful method is exemplified using Mg2Sn (an end member of the highly popular Mg2(Si,Sn) solid solutions), chosen due to its low band gap and the availability of experimental data in a wide range of dopant concentrations. Using the experimental data for p- and n-type Mg2Sn from literature, a two-band model was obtained and optimum carrier concentration and maximum zT were predicted. At 650 K, pronounced differences between the SPB and the two-band model, which could prevent realisation of maximum zT, were observed demonstrating the practical necessity to model the effect of minority carriers.

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Efficiency as a performance metric for material optimization in thermoelectric generators

Cited by 6 publications

References 40 publications

Overcoming Asymmetric Contact Resistances in Al-Contacted Mg2(Si,Sn) Thermoelectric Legs

Overcoming Asymmetric Contact Resistances in Al-Contacted Mg2(Si,Sn) Thermoelectric Legs

High‐Performance Thermoelectric Devices Made Faster: Interface Design from First Principles Calculations

Developing a two-parabolic band model for thermoelectric transport modelling using Mg₂Sn as an example

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Efficiency as a performance metric for material optimization in thermoelectric generators

Cited by 6 publications

References 40 publications

Overcoming Asymmetric Contact Resistances in Al-Contacted Mg2(Si,Sn) Thermoelectric Legs

Overcoming Asymmetric Contact Resistances in Al-Contacted Mg2(Si,Sn) Thermoelectric Legs

High‐Performance Thermoelectric Devices Made Faster: Interface Design from First Principles Calculations

Developing a two-parabolic band model for thermoelectric transport modelling using Mg2Sn as an example

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Developing a two-parabolic band model for thermoelectric transport modelling using Mg₂Sn as an example