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Page 2 of 17 Kumar et al. Energy Mater. 2025, 5, 500109 https://dx.doi.org/10.20517/energymater.2025.22

INTRODUCTION
Thermoelectric (TE) devices, which can directly enable waste heat recovery or eco-friendly solid-state
cooling through the Seebeck effect and Peltier effect, respectively, have a wide range of interesting
application fields. These include thermoelectric generators (TEGs), thermoelectric cooling devices, wearable
TE devices, power systems for the Internet of Things (IoT), medical devices requiring sensitive temperature
control, radioisotope thermoelectric generators (RTGs), battery thermal management systems for electric
[1-3]
vehicles, and more . Despite their advantages, such as direct energy conversion between heat and
electricity, absence of moving parts, scalability, portability, eco-friendly operation, and low-grade heat
recovery, the use of TE devices is limited in certain applications due to their relatively low energy
conversion efficiency compared to other electricity generation or cooling systems [1,2,4] . Therefore, improving
the thermoelectric performance of TE devices is essential to expand their range of applications.

The energy conversion efficiency of a TE device strongly depends on the dimensionless figure of merit (ZT)
of the p- and n-type TE materials, defined as ZT = S σT/κ , where S is the Seebeck coefficient, σ is the
2
total
electrical conductivity, T is the absolute temperature and κ is the total thermal conductivity. Since these
total
parameters are strongly interrelated, careful control of the material properties is required to enhance TE
performance [1,2,4] . Various approaches can improve materials’ TE performance, such as optimizing carrier
concentration, reducing lattice thermal conductivity (κ ), manipulating the band structure, employing
L
low-dimensional structures, low-energy electron filtering, introducing defects, and leveraging resonant
[2,5]
levels .
Bismuth tellurides are among the most well-known thermoelectric materials, exhibiting high performance
near room temperature [1,4,6,7] . Their high ZT values have been achieved through various innovative
approaches for the p-type bismuth antimony tellurides such as the hot-deformed Bi Sb Te (1.3 at
0.3
1.7
3
380 K) , Te-excess Bi Sb Te (ZT = 1.41 at 417 K) , liquid phase sintered Ag Bi Sb Te (1.36 at
[9]
[8]
1.5
x
1.6
3
0.4
0.5
3.4
[10]
[11]
400 K) , melt-spun Bi Sb Te (1.24 at 350 K ) and n-type bismuth tellurides such as the CuI-doped
3
0.5
1.5
[12]
[13]
Bi Te Se (1.07 at 423 K) , Ag SnSe -incorporated Bi Te Se Cl (1.24 at 353 K) , graphitic carbon
2
0.03
2.69
8
0.33
6
2
0.3
2.7
[14]
nitride-decorated Bi Te Se (1.29 at 400 K) , etc. However, thermoelectric energy conversion efficiency of
2.7
0.3
2
bismuth tellurides remains insufficient for broader applications. Therefore, efficient and practical strategies
to further improve ZT values are required [1,2,4] .
During two decades, the phonon-glass and electron-crystal (PGEC) concept has been investigated as of
critical importance in thermoelectric materials development . The PGEC in Bismuth Tellurides has been
[15]
adopted by incorporating nanoparticle distribution in the matrix. However, the nanoparticle distribution in
the Bi Sb Te (BST) matrix mainly focused on the decreasing κ rather than the increase of electrical
L
0.4
1.6
3
transport property. Here we adopt the heavy metallic high entropy alloy composite to realize the PGEC in
the BST matrix.
High-entropy alloys (HEAs), which consist of the multi-component mixing of five or more elements in
near-equimolar concentrations, are considered promising candidates for high-performance thermoelectric
materials. Their potential arises from low κ due to lattice distortions caused by atomic mass and size
L
mismatches [16,17] . HEAs exhibit unique properties such as exceptional strength, ductility, and thermal
stability, making them attractive for thermoelectric applications in extreme environmental conditions [18-20] .