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Page 2 of 33 Girase et al. Energy Mater. 2025, 5, 500132 https://dx.doi.org/10.20517/energymater.2025.14

However, the world’s fast-growing demand for electricity cannot be met by fossil fuel technologies.
Therefore, an urgent and essential need to develop alternative energy conversion technologies to meet the
[1]
energy requirement challenge . However, most renewable energy conversion devices have fundamental
limitations on their maximum conversion efficiency, which is at the best less than 40%, with a significant
part of that energy dissipated into the environment as heat . Therefore, to address global environmental
[2]
challenges and provide new opportunities for the usage of renewable energy resources, it is imperative to
develop novel technologies with higher energy conversion efficiency and less waste heat. Recently,
thermoelectric (TE) and photovoltaic (PV) technologies have emerged as two viable clean, sustainable
energy conversion methods to address the energy crisis from an environmental and sustainable standpoint.

Significant progress has been achieved in the development of PV materials over the past ten years, but the
research in the field of TE is still behind. Unlike photovoltaic techniques, TE technology has shown
remarkable performance, as TE devices rely not only on solar energy but also on various heat sources,
including body heat, which is a promising and alternative energy source for the future . TE materials hold
[3]
immense promise for powering a wide range of low-power technologies due to their ability to convert waste
heat into electricity. One of the most attractive features of TE generators (TEGs) is their scalability and
maintenance-free operation, making them ideal for small-scale and remote applications. This makes them
excellent candidates for portable and wearable electronics. Additionally, TEGs are increasingly used to
[4]
power low-energy devices such as radiator valves (Micropelt), wireless sensor nodes , and industrial
[5]
monitoring systems . In the biomedical field, TE materials are particularly valuable for powering
[6,7]
biosensors and implants by harvesting body heat , thus eliminating the need for external power sources.
Beyond healthcare, TEGs are beneficial in environments where solar energy harvesting is not viable, such as
in mines, pipelines, and aircraft. In such critical or hazardous zones, TE-based sensors offer reliable
solutions for fire detection, homeland security, and environmental monitoring .
[8,9]

Traditional TE devices are generally based on inorganic materials due to their superior TE performances
and stability over organic materials. The inorganic materials such as lead telluride (PbTe) , bismuth
[10]
[12]
telluride (Bi2Te3) , silicon-germanium (SiGe) and tin selenide (SnSe) are extensively studied, where
[11]
[13]
the ZT value (dimensionless merit figure) reaches to 2.6 [14-17] . On the downside, many in organic
semiconductor (OSC) materials have certain disadvantages inherent to the material, such as scarcity, toxic
nature, inadequate processability, high thermal conductivity, and high manufacturing cost. In the recent
years, research on carbon nanotube (CNT)-based are promising TE materials. Single-walled CNTs
(SWCNTs) are highly promising for thermoelectrics due to their high conductivity, ease of doping, and
surface functionalization. Their charge carrier type and density can be tuned through chemical doping,
though stable n-type doping remains a challenge. Forming CNT-based composites with organic or
inorganic materials enhances TE performance by combining high conductivity, improved Seebeck
coefficient (S), and low thermal conductivity (κ) [18,19] . On the other hand, OSCs have been neglected for
decades because of their low energy conversion efficiency and potential bad thermal stability, but they are
potential candidates for the conversion of low-grade thermal energy into useful electricity, as they possess
[20]
low-cost, lightweight, and mechanically flexible properties compared to classical in OSCs . Over the past
several decades, extensive research has been dedicated to the development and modification of organic
polymers and molecules with promising performance capabilities for use as TE materials . Figure 1
[21]
demonstrates an increase in the number of research publications conducted in TE (keyword as
thermoelectric polymer) which shows the significant efforts that have been made in the field of TE. Despite
the current challenge presented by the low κ value of polymers, which remains an ongoing issue that
researchers are striving to overcome, there have been many reports of organic TE materials exhibiting ZT
values greater than 1, attributed to their advantageous traits of high electrical conductivities along with