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Page 24 of 35 Martin-Gonzalez et al. Energy Mater. 2025, 5, 500121 https://dx.doi.org/10.20517/energymater.2025.32

studied method is the so-called band alignment (or band-convergence) in which multi-band electronic
structures undergo specific alloying such that many bands are aligned in energy and all contribute to
transport. Many other concepts are explored, such as resonant states, topological effects, defect engineering,
and transport in low bandgap materials and/or semimetals. The exploration of these newly emerged
physics-based concepts and their integration into different materials is only the starting point, and many
exciting outcomes are expected in the future in the field of thermoelectrics.

However, the transition from thermoelectric materials to TEG devices presents its own set of challenges that
must be addressed for successful commercialization of these materials with high efficiency. Key issues
include interface engineering, where the complexity of interfaces between different TE materials can lead to
increased thermal and electrical contact resistance, negatively impacting efficiency. Material degradation
during operation, particularly due to chemical reactions with moisture and diffusion processes, can
compromise the integrity and performance of the modules. Additionally, careful matching of thermal
expansion coefficients is crucial to prevent mechanical stresses that can lead to cracking and delamination.
The soldering and bonding processes used to connect TE materials to electrodes also present challenges, as
traditional soldering materials may not provide adequate thermal and electrical conductivity. Finally, the
mechanical stability of TEGs under varying thermal and mechanical loads must be ensured to withstand
harsh environments and repeated thermal cycling. Addressing these challenges is essential for the successful
integration of TEG technology into practical applications, and ongoing research is vital to optimize
materials for stability, performance, and cost-effectiveness.

DECLARATIONS
Acknowledgments
The authors acknowledge funding from the European Research Council (ERC) under the European Union’s
Horizon 2020 Research and Innovation Programme ERC Advanced and ERC Starting Grant.

Authors’ contributions
Conceptualization, data curation, writing - original draft: Martin-Gonzalez, M.
Data curation, writing: Lohani, K.
Conceptualization, data curation, writing - original draft: Neophytou, N.

Availability of data and materials
Not applicable.

Financial support and sponsorship
This work was supported by a Grant named ERC Advanced (POWERbyU Grant Agreements No.
101052603) and ERC Starting Grant (NANOthermMA grant agreement No. 678763).

Conflicts of interest
All authors declared that there are no conflicts of interest.

Ethical approval and consent to participate
Not applicable.

Consent for publication
Not applicable.