Electrical Contacts Characterization of Tetrahedrite-Based Thermoelectric Generators

At a Glance

Metadata	Details
Publication Date	2022-06-08
Journal	MATERIAIS 2022
Authors	Rodrigo Coelho, Yassine De Abreu, Francisco Carvalho, Elsa B. Lopes, A.P. Gonçalves
Institutions	Instituto Politécnico de Lisboa, University of Lisbon
Citations	1
Analysis	Full AI Review Included

Technical Documentation & Analysis: Electrical Contacts for Thermoelectric Generators

This document analyzes the research concerning electrical contact characterization in tetrahedrite-based thermoelectric generators (TEGs). It highlights the critical role of precision material processing and low-resistance interfaces, directly correlating the experimental requirements with the advanced capabilities offered by 6CCVD’s MPCVD diamond materials and fabrication services.

Executive Summary

Application Focus: Optimization of electrical contacts for high-efficiency, low-cost Tetrahedrite (Cu₁₁Mn₁Sb₄S₁₃) Thermoelectric Generators (TEGs).
Core Challenge: Minimizing high electrical and thermal resistivities at the interface between the tetrahedrite legs and copper electrodes, which critically degrades TEG performance.
Methodology: Researchers explored various jointing techniques, including cold-pressing, hot-pressing, and the use of Ni paint, Ag water-based paint, and Zn-Al 5 wt% solder.
Material Preparation: Tetrahedrite legs were precisely shaped into small cubes (~7 x 7 mm) using a Diamond saw, emphasizing the need for high-precision material processing.
Analysis: Contact resistance was measured using a three-point pulsed current method, and the resulting data was used in COMSOL Multiphysics simulations to predict device performance (IV/IP plots).
6CCVD Value Proposition: The requirement for precision shaping, ultra-low surface roughness, and robust metalization aligns perfectly with 6CCVD’s capabilities in custom MPCVD diamond substrates (SCD/PCD) and advanced thin-film deposition.

Technical Specifications

The following parameters were extracted from the methodology and context of the research paper, defining the scope of the material requirements for high-performance TEG contacts.

Parameter	Value	Unit	Context
Thermoelectric Material	Cu₁₁Mn₁Sb₄S₁₃	N/A	Tetrahedrite compound used for TEG legs
Leg Dimensions (Target)	~7 x 7	mm	Small cubes requiring precision cutting
Electrode Material	Copper	N/A	Used for electrical contacts
Solder Composition Tested	Zn-Al 5 wt%	N/A	One of the jointing materials explored
Operating Temperature Range (zT)	350 to 650	K	Range where average zT ≥ 0.4 is observed
Contact Measurement Technique	Three-point pulsed current	N/A	Used in a custom set-up to quantify resistance
Simulation Tool	COMSOL Multiphysics	N/A	Used to model current-voltage (IV) and current-power (IP) plots

Key Methodologies

The experiment focused on the fabrication and characterization of the tetrahedrite-copper interface. The key steps involved in material preparation and contact formation were:

Material Synthesis: Cu₁₁Mn₁Sb₄S₁₃ tetrahedrite legs were synthesized via a solid-state reaction.
Sintering: The synthesized material was consolidated using hot-pressing techniques.
Precision Shaping: The sintered materials were shaped into small cubes (~7 x 7 mm) using a Diamond saw to ensure dimensional accuracy for device assembly.
Contact Fixation Methods: Different mechanical methods were tested, including cold-pressing (CP), hot-pressing (CP), and manual preparation.
Jointing Material Testing: Various interface materials were applied, including Ni paint, Ag water-based paint, and Zn-Al 5 wt% solder.
Characterization: Electrical contact resistance was measured using a custom-made set-up based on the three-point pulsed current method.
Performance Modeling: Measured resistance values were integrated into COMSOL Multiphysics simulations to predict the final TEG performance.

6CCVD Solutions & Capabilities

The successful replication and advancement of this research require materials with extreme dimensional precision, ultra-low surface roughness, and robust, customized metalization layers—all core competencies of 6CCVD.

Applicable Materials

To replicate or extend the performance of high-efficiency TEGs, 6CCVD recommends the following materials, often used as high-performance substrates or heat spreaders in similar high-power density applications:

Optical Grade Single Crystal Diamond (SCD): Ideal for applications requiring the highest possible thermal conductivity (heat spreading) and ultra-low surface roughness (Ra < 1nm). SCD can serve as a highly stable, dimensionally precise substrate for mounting the TEG legs.
Polycrystalline Diamond (PCD) Wafers: Recommended for larger area devices (up to 125mm) where cost-effectiveness and high thermal stability are required. PCD can be polished to Ra < 5nm, providing an excellent base for low-resistance metal contacts.

Customization Potential

The research utilized diamond saw cutting and tested various metal interfaces (solder, paints). 6CCVD provides the necessary precision engineering to eliminate variability introduced by manual preparation and ensure optimal contact quality:

Research Requirement	6CCVD Capability	Technical Benefit
Precision Shaping (7 x 7 mm cubes)	Custom Dimensions & Laser Cutting: We offer plates/wafers up to 125mm and provide high-precision laser cutting and grinding services.	Ensures highly accurate, repeatable dimensions for TEG legs and substrates, minimizing geometric resistance and maximizing thermal uniformity.
Low-Resistance Interface	Ultra-Smooth Polishing: SCD polishing to Ra < 1nm; PCD polishing to Ra < 5nm.	Provides an atomically flat surface essential for achieving uniform bonding and minimizing parasitic contact resistance when applying solders or thin-film metal layers.
Robust Electrical Contacts	Custom Metalization: In-house deposition of Ti, Pt, Au, Pd, W, and Cu.	Allows researchers to test specific low-ohmic contact stacks (e.g., Ti/Pt/Au) directly onto the diamond substrate, offering superior adhesion and stability compared to paints or solders alone.
High-Temperature Stability	Diamond Substrates: SCD/PCD are chemically inert and stable up to 1000 °C (in inert atmosphere).	Guarantees material integrity and contact stability across the required operating temperature range (350 K to 650 K) and during hot-pressing fabrication steps.

Engineering Support

6CCVD’s in-house PhD team specializes in the material science of diamond interfaces and thin-film deposition. We can assist researchers and engineers with material selection, surface preparation protocols, and metal stack design specifically tailored for high-temperature, low-resistance interfaces required in Thermoelectric Generator (TEG) projects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We offer global shipping (DDU default, DDP available) for rapid delivery of custom diamond solutions.

View Original Abstract

first_page settings Order Article Reprints Font Type: Arial Georgia Verdana Font Size: Aa Aa Aa Line Spacing:    Column Width:    Background: Open AccessAbstract Electrical Contacts Characterization of Tetrahedrite-Based Thermoelectric Generators † by Rodrigo Coelho 1,*, Yassine De Abreu 2, Francisco Carvalho 3, Elsa B. Lopes 1 and António P. Gonçalves 1 1 C2TN, DECN, Instituto Superior Técnico, Campus Tecnológico e Nuclear, Universidade de Lisboa, 2695-066 Loures, Portugal 2 CESI, Campus D’enseignement Supérieur et de Formation Professionnelle, 15C Av. Albert Einstein, Villeurbanne, 69100 Lyon, France 3 DEEC, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal * Author to whom correspondence should be addressed. † Presented at the Materiais 2022, Marinha Grande, Portugal, 10-13 April 2022. Mater. Proc. 2022, 8(1), 87; https://doi.org/10.3390/materproc2022008087 Published: 8 June 2022 (This article belongs to the Proceedings of MATERIAIS 2022) Download Download PDF Download PDF with Cover Download XML Download Epub Versions Notes Thermoelectric generators (TEGs) are devices capable of harvesting waste heat and directly converting it into electricity through the Seebeck effect. They have no moving parts and emit neither toxic nor greenhouse gasses. These devices have high modularity and low maintenance needs, making them very promising to fight against global warming. At the same time, with the rapid growth in energetic needs and the efforts from industries to become greener, the market for TEGs is boosting the search for more efficient and cheaper materials. One such new material, seen as having great potential for thermoelectric applications, is copper antimony sulfosalts. These materials are very cheap (~USD 7 [1]), can be found in nature, have good thermoelectric properties (average zT ≥ 0.4 between 350 K and 650 K [2]), and present low toxicities. However, tetrahedrite-based TEGs are still under development, with the fabrication of good electrical contacts between tetrahedrites and the copper electrodes (that form the device) being one of the biggest challenges to produce efficient and commercially competitive generators. Since high electrical and thermal resistivities can ruin the performance of TEGs, such problems can be also found in commercial devices. However, there are just a few public studies focused on measuring and characterizing the electrical contacts, with most of the jointing fabrication techniques being patented or classified [3].In the present work, diverse contact fabrication techniques are explored to evaluate the most suitable methods to connect Cu11Mn1Sb4S13 tetrahedrites to copper electrodes. The tetrahedrite legs were synthetized by a solid-state reaction and sintered by hot-pressing. Then, the materials were shaped into small cubes (~7 × 7 mm) using a Diamond saw and connected to copper plates (~7 × 7 mm) using different techniques. Contact fixation methods such as cold-pressing (CP) and hot-pressing (CP) were used, with some legs also being prepared manually. Together with the different preparation methods, several paints and resins were used for jointing. In summary, Ni and Ag water-based paints and a Zn-Al 5 wt% solder were tested. The possibility of contact fabrication without the use of any paints or solders was also explored by using our hot-pressing equipment.The contact resistance between the tetrahedrites and the copper contacts was measured in a custom-made set-up based on the three-point pulsed current method. To achieve a better understanding on how the contact quality affects the final performance of a tetrahedrite based TEG, several computer simulations were made using the COMSOL Multiphysics software. The previously measured contact resistance values were considered on the simulations, and the respective current-voltage (IV) and current-power (IP) plots for a thermocouple were obtained. The main results of this study on how different fabrication methods and jointing materials affect the electrical contact resistance and the performance of a tetrahedrite based TEG will be presented. Author ContributionsConceptualization, A.P.G. and R.C.; methodology, R.C.; software, E.B.L.; validation, R.C., E.B.L. and A.P.G.; formal analysis, R.C., E.B.L. and A.P.G.; investigation, R.C., Y.D.A. and F.C.; resources, E.B.L. and A.P.G.; data curation, R.C., Y.D.A. and F.C.; writing—original draft preparation, R.C., E.B.L. and A.P.G.; writing—review and editing, R.C., E.B.L. and A.P.G.; visualization, R.C., E.B.L. and A.P.G.; supervision, E.B.L. and A.P.G.; project administration, E.B.L. and A.P.G.; funding acquisition, R.C., E.B.L. and A.P.G. All authors have read and agreed to the published version of the manuscript.FundingThis work was supported by the Portuguese Foundation for Science and Technology (FCT), Portugal, through the contracts UID/Multi/04349/2020 and UI/BD/150713/2020.Institutional Review Board StatementNot Applicable.Informed Consent StatementNot Applicable.Data Availability StatementNot Applicable. Conflicts of InterestThe authors declare no conflict of interest.ReferencesGonçalves, A.P.; Lopes, E.B.; Monnier, J.; Alleno, E.; Godart, C.; Montemor, M.; Vaney, J. Tetrahedrites for low cost and sustainable thermoelectrics. Solid State Phenom. 2017, 257, 135-138. [Google Scholar] [CrossRef]Coelho, R.; Symeou, E.; Kyratsi, T.; Gonçalves, A.P. Tetrahedrite sintering conditions: The Cu11Mn1Sb4S13 case. J. Electr. Mater. 2020, 49, 5077-5083. [Google Scholar] [CrossRef]Ren, Z.; Lan, Y.; Zhang, Q. (Eds.) Advanced Thermoelectrics, Materials, Devices, Contacts and Systems; Taylor & Francis Group LLC.: New York, NY, USA, 2017. [Google Scholar] [CrossRef]Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). Share and Cite MDPI and ACS Style Coelho, R.; De Abreu, Y.; Carvalho, F.; Lopes, E.B.; Gonçalves, A.P. Electrical Contacts Characterization of Tetrahedrite-Based Thermoelectric Generators. Mater. Proc. 2022, 8, 87. https://doi.org/10.3390/materproc2022008087 AMA Style Coelho R, De Abreu Y, Carvalho F, Lopes EB, Gonçalves AP. Electrical Contacts Characterization of Tetrahedrite-Based Thermoelectric Generators. Materials Proceedings. 2022; 8(1):87. https://doi.org/10.3390/materproc2022008087 Chicago/Turabian Style Coelho, Rodrigo, Yassine De Abreu, Francisco Carvalho, Elsa B. Lopes, and António P. Gonçalves. 2022. “Electrical Contacts Characterization of Tetrahedrite-Based Thermoelectric Generators” Materials Proceedings 8, no. 1: 87. https://doi.org/10.3390/materproc2022008087 Find Other Styles Note that from the first issue of 2016, MDPI journals use article numbers instead of page numbers. See further details here. Article Metrics No No Article Access Statistics Multiple requests from the same IP address are counted as one view.

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Original Source

DOI: https://doi.org/10.3390/materproc2022008087

References

2017 - Tetrahedrites for low cost and sustainable thermoelectrics
2020 - Tetrahedrite sintering conditions: The Cu11Mn1Sb4S13 case [Crossref]