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Page 22 of 35 Martin-Gonzalez et al. Energy Mater. 2025, 5, 500121 https://dx.doi.org/10.20517/energymater.2025.32

semiconductors (SiC, GaN) to handle maximum power point tracking (MPPT) at > 90% efficiency [299-301] .
Moreover, heterogeneous integration using ultra-deep through-silicon vias (TSVs) reduces parasitic
[302]
resistance in Si-based devices .

Finally, the performance testing and its optimization is something that must also be researched to be able to
transition from high zT materials to high ZT devices. The performance of TEG modules must be rigorously
tested under various conditions to ensure reliability and efficiency. This includes evaluating their
performance, along with other parameters such as internal resistance, and overall stability of the modules
under different atmospheric conditions and temperature cycles. While significant advancements have been
made in the development of TE materials, each category presents specific challenges that must be addressed
to facilitate their transition into the market. Ongoing research is essential to optimize these materials for
stability, performance, and cost-effectiveness, ensuring their viability for commercial application.

Several examples of the transformation from materials to functioning TE devices - with increasing overall
device efficiency and their key limitations - have been reported in the literature, as discussed in Table 4.
Various materials such as Mg Sb 2 [309] , GeTe , and half-Heusler phase compounds-based TE modules
[311]
[318]
3
have demonstrated efficiencies exceeding 10% across diverse temperature gradients, which is higher than
commercially available Bi Te -based modules. For example, NASA has been employing SiGe- and PbTe-
2
3
based TE modules in various space exploration missions, with an efficiency of 6.3% at a temperature
gradient of 700 K and 328 K for SiGe- and PbTe-based systems, respectively .
[323]
Lastly, it is vital to consider the market positioning of TE modules in relation to competing technologies.
From an energy generation perspective, alternatives such as internal combustion engines (ICEs), organic
Rankine cycle (ORC) systems, photovoltaics (PV), fuel cells, and piezoelectric or triboelectric generators
pose significant competition. For refrigeration applications, vapor compression systems (VCS),
magnetocaloric refrigeration (MCR), phase-change materials, and microfluidic cooling are key rivals.
Currently available TE systems, which exhibit an efficiency of around ~10% as generators and a coefficient
of performance (COP) of less than 1 as coolers, offer lower performance compared to ICEs, PV, and fuel
cells. The same is true when compared to VCS and MCR. However, their solid-state nature, reliability, low
maintenance, and size versatility make them viable for a wide range - from large-scale systems to
microelectronic devices, including various autonomous and sensor applications. In a similar vein, cooling
using thermoelectric coolers (TECs) offers higher precision and control, and their compact nature enables
easy and scalable integration. In fact, integration of thermoelectrics with other sustainable solutions such as
PV and ICEs has shown improvement in the overall system efficiency. It is also important to note that TEGs
outperform piezoelectric and triboelectric generators, and TECs can be an effective cooling solution for
microelectronics. It is worth mentioning that while TEGs excel in niche applications - such as wearables ,
[296]
space power - they face stiff competition from ORCs in waste heat recovery scenarios. Techno-economic
[306]
-2
analyses indicate that TEGs become commercially viable at heat fluxes exceeding 5 W·cm , where ORC
[324]
systems struggle due to high maintenance costs . Recent advances include the demonstration of a 600 W
TEG prototype integrated into a BMW X6, highlighting progress toward the U.S. Department of Energy’s
$1/W cost target [325,326] for automotive applications. In parallel, material innovations such as Cu/Ag co-
doping in bismuth telluride alloys have been shown in laboratory studies to reduce tellurium content by up
to 40%, potentially contributing to future cost reductions, while also working on element recovery after the
car is not more in use. One promising solution lies in circular economy approaches, such as the
electrochemical recovery of critical elements like copper, bismuth, tellurium, and antimony commonly used
in TE modules [327,328] .