Substitution energy-guided screening of diffusion barrier materials for Ag2Se-based thermoelectric coolers

Thermoelectric technology enables the direct conversion between heat and electricity based on the Seebeck and Peltier effects, and can be used for both power generation and refrigeration. However, the development of thermoelectric devices has progressed slowly due to the persistent challenges in designing highly reliable diffusion barrier materials (DBMs). DBMs play a critical role in preventing interdiffusion and chemical reactions between the thermoelectric material and the electrode, while also ensuring low interfacial contact resistivity (ρ_c) and strong mechanical bonding during long-term operation. As such, the performance stability and structural reliability of thermoelectric devices largely depend on the effectiveness of the DBM. The conventional DFT-based screening approach necessitates the calculation of interface reaction energies (E_IR) for all possible reactions, leading to substantial computational costs and low efficiency.

A joint team led by Lei Miao from Guangxi University and Zhi-Gang Chen from Queensland University of Technology recently introduced an efficient screening approach that employs substitution energy (E_Sub) as a surrogate for E_IR, significantly reducing computational demand. By integrating E_Sub with migration energy barriers (E_Mig), Ni is identified as a robust DBM for Ag₂Se. Experimental validation confirms that Ni/Ag₂Se joints exhibit low contact resistivity (6.6 μΩ cm²) and high thermal stability after 30 days of thermal aging. The Te-free Ag₂Se/MgAgSb devices achieve a maximum cooling temperature difference of 68 K at 350 K, comparable to state-of-the-art Ag₂Se/Bi₂Te₃ devices, while demonstrating excellent durability over 2000 power cycles. This strategy offers a rapid and reliable framework for DBM selection, accelerating the advancement of high-performance thermoelectric devices.

The team published their research article in Nano Research on September 29, 2025.

“In this work, we present a streamlined approach for DBM screening in metal chalcogenide-based devices, adopting E_Sub as a simplified criterion within the conventional DFT-based framework. Using Ag₂Se as a case study, Ni was identified as a reliable DBM for Ag₂Se-based devices.” said Lei Miao, corresponding author of the research article, professor in the School of Physical Science and Technology at Guangxi University. Dr. Miao is also the visiting researcher at the Materials Technology Research Institute of the Japan Fine Ceramics Research Center.

In recent years, several more precise strategies for DBM screening have been proposed, including high-throughput methods, phase diagram calculations, and DFT simulations. Among them, the DFT-based strategy is grounded in the theory of solid-state diffusion reactions. It involves calculating the E_IR between DBM candidates and thermoelectric materials, as well as the E_Mig of diffusing atoms. Generally, suitable DBMs are typically screened based on having an E_IR close to zero and a sufficiently large E_Mig. However, a key limitation of this approach is the potential formation of multiple interfacial reaction products. Since the actual reaction products cannot be precisely predicted, it is necessary to calculate the E_IR for all possible reactions, resulting in a substantial computational burden.

For substitution-type interfacial reactions (A + BC → AC + B), particularly those occurring between pure metals and metal chalcogenides (e.g., Ag₂Q and Cu₂Q, where Q = S, Se, Te), the high electronegativity of chalcogens (S: 2.58, Se: 2.55, Te: 2.10) drives their preferential bonding with most pure metals. This often results in the formation of stable compounds and the precipitation of Ag or Cu. Accordingly, the chemical reactivity of DBM candidates can be assessed based on the E_Sub of DBM atoms replacing Ag or Cu atoms in the host lattice. A lower E_Sub indicates a more energetically favorable substitution reaction, suggesting a higher likelihood of interfacial reactivity, consistent with trends predicted by E_IR. The E_Sub-based screening approach enables efficient evaluation of chemical compatibility between DBMs and metal chalcogenides, requiring only a single substitution energy calculation without the need to explore all possible reaction pathways. In this study, n-type Ag₂Se thermoelectric material is investigated as a representative case. Based on the E_Sub of DBM atoms substituting Ag sites in the Ag₂Se lattice, and the E_Mig for DBM atoms diffusing into neighbouring Ag vacancies, Ni is rapidly identified as a promising DBM candidate. Experimental results confirm that Ni/Ag₂Se joints exhibit low ρ_c during long-term thermal aging. A device comprising seven pairs of Ag₂Se/MgAgSb legs, with Ni employed as the DBM for the Ag₂Se legs, demonstrates excellent cooling performance and high reliability.

Other contributors include Shiyuan Zhao, Qi Zhou, Zhongwei Zhang, Jisheng Liang, Zhengniu Pan and Sijing Zhu from the School of Physical Science and Technology at Guangxi University in Guangxi, China; and Xiao-Lei Shi, Meng Li and Wenyi Chen from the School of Chemistry and Physics at Queensland University of Technology in Queensland, Australia; and Jun-Liang Chen and Jie Gao from the Engineering Research Centre of Electronic Information Materials and Devices at Guilin University of Electronic Technology in Guilin, China; and Tomohiro Sato from the Sinter Land Inc. in Niigata, Japan.

This work was supported by the National Natural Science Foundation of China (Grant No. U21A2054), the National Natural Science Foundation of China (Grant No. 51961011, 52273285). Z.-G. C. thanks the financial support from the Australian Research Council, HBIS-UQ Innovation Centre for Sustainable Steel project, and the QUT Capacity Building Professor Program. This work was enabled by using the Central Analytical Research Facility hosted by the Institute for Future Environments at QUT.

About Nano Research

Nano Research is a peer-reviewed, open access, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society, published by Tsinghua University Press on the platform SciOpen. It publishes original high-quality research and significant review articles on all aspects of nanoscience and nanotechnology, ranging from basic aspects of the science of nanoscale materials to practical applications of such materials. After 18 years of development, it has become one of the most influential academic journals in the nano field. Nano Research has published more than 1,000 papers every year from 2022, with its cumulative count surpassing 7,000 articles. In 2024 InCites Journal Citation Reports, its 2024 IF is 9.0 (8.7, 5 years), and it continues to be the Q1 area among the four subject classifications. Nano Research Award, established by Nano Research together with TUP and Springer Nature in 2013, and Nano Research Young Innovators (NR45) Awards, established by Nano Research in 2018, have become international academic awards with global influence.