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Chen et al. Energy Mater. 2025, 5, 500120 https://dx.doi.org/10.20517/energymater.2024.311 Page 3 of 21

materials from existing literature based on knowledge of materials synthesis and the prediction and control
of outcome is complicated. This is because the control over TE materials synthesis depends on carefully
controlling many experimental parameters such as choice of precursors, synthetic methods, temperature,
pressure, atmosphere, time, additives, etc.

There are a total of 38,413 published articles under the keyword 'thermoelectric materials' over the past ten
years in the Science Direct database. Figure 1 shows how publication activity in TE materials has changed
over the last ten years. The surge in TE materials research is apparent, and the number of publications has
increased rapidly. Therefore, the research areas involving TE materials are popular among the scientific
community. However, controllable synthesis of TE materials is a significant bottleneck for realizing
practical thermoelectric devices such as TEGs. Notably, there is a knowledge gap between implementing
statistical optimization methodologies, discovering new TE materials, and finding optimal synthesis and
device fabrication conditions. This article covered the importance of ML in DOE for TE material synthesis,
material chemistry parameters involving boosting TE performance, segregating materials based on
performance, finding new material, and optimizing composition. In TE material creation such as a thin
film, the ML approach in parameter optimization for coating and sintering is discussed.

PERFORMANCE ENHANCEMENT OF THERMOELECTRIC MATERIALS
The efficiency of TEGs depends on the performance of TE materials. In this direction, significant
advancement has been achieved through research and development toward the optimal performance of TE
materials [13-19] .

The performance of TE materials is usually expressed as the “figure of merit” ZT = S σT/ κ + κ, where the
2
l
e
Seebeck coefficient is S, the electrical conductivity is σ, and electronic and lattice thermal conductivities are
κ and κ espectively, at temperature T. Here (κ + κ) is known as the total thermal conductivity of TE
l
e
l
e
materials. Thus, a high value of ZT implies high performance of TE materials. Moreover, TE materials with
high ZT values can lead to efficient TE devices for commercial applications. The high value of ZT at a given
temperature can be achieved with TE materials having high S, high σ, and low thermal conductivities κ and
e
κ. However, σ decreases when S increases. On the other hand, total thermal conductivity (κ + κ) of TE
l
l
e
materials is proportional to σ. Due to this complex interrelation between the TE parameters, it is pretty
challenging to control independent parameters experimentally for the optimization of the performance of
TE materials. Literature-reported methods for optimizing ZT focused on the methods for reducing thermal
conductivity and enhancing S and σ, respectively [17,20] . Finally, when the thermal conductivity of materials is
2
very low or unavailable, the performance of TE materials can be expressed as the power factor S σ.
Thermoelectric materials development
The range of materials that exhibit TE properties encompasses wide varieties, including inorganic, organic,
[21]
and inorganic-organic hybrid . Naturally, each type of material has its advantages and disadvantages.
There are vast numbers of inorganic materials that exhibit TE properties. Typical inorganic TE materials are
based on chalcogenides (such as Bi Te , PbTe, SnSe, etc.), Si-Ge alloys, multicomponent oxides,
2
3
skutterudite-type materials, half-Heusler alloys, and clathrates [14,19] . The variation of ZT with temperature of
some typical inorganic TE materials is shown in Figure 2 . As a result of extensive research and
[22]
development over the past few decades, Bi Te and Si-Ge-based materials are used in commercial TE
2
3
devices. The main advantage of inorganic TE materials is their high TE performance. Commercial TE
devices use inorganic materials with ZT~1. Therefore, searching for new materials with high ZT values has
been popular in TE material research [20,23] . The disadvantages of inorganic TE materials include poor
abundance of elements, high cost, and toxicity . On the other hand, the advantages of organic TE materials
[24]