The rapid evolution of wearable technology has driven a surge in demand for sustainable, self-powered electronic devices. Flexible thermoelectric materials, capable of converting body heat into electricity, have emerged as a promising solution for powering next-generation wearables. This review comprehensively examines recent progress in organic (polymer-based) and hybrid thermoelectric materials, focusing on their design, fabrication, and integration into flexible architectures suitable for conformal contact with human skin. Key developments include advanced doping strategies, post-treatment techniques, and composite engineering, particularly in conductive polymers such as PEDOT: PSS and P3HT, which have significantly enhanced power factors and mechanical flexibility. Additionally, the integration of high-performance inorganic materials into stretchable systems has further elevated device efficiency and durability. The review highlights breakthroughs, ongoing challenges, and future opportunities in realizing practical, scalable, and high-efficiency wearable thermoelectric generators for sustainable energy harvesting applications.

The continuous and long-lasting monitoring of physiological signals induced from the human body is crucial for health monitoring, disease diagnosis, and treatment. In this study, we have reported the Seebeck effect-based flexible selfpowered temperature sensor which can convert the electric signals from lateral temperature difference. For demonstrating temperature sensor arrays, the p-type thermoelectric (TE) composite films were fabricated by dispersing the Bi_0.5Sb_1.5Te₃ (BST) powders inside poly-vinylidene fluoride matrix and subsequently attached to the patterned electrode foils. The inorganic BST powders-embedded TE composite films with activated area of 0.5 × 1 cm² harvest a maximum voltage of 1.7 mV, a maximum current of 5.6 mA, and an output power of 2.6 nW from the temperature gradient (ΔT) of 20 K. Finally, the fabricated selfpowered temperature sensor array well detected the pattern images of external thermal source of ΔT = 20 K. This study manifests flexible temperature sensor array which paves the way for further advancements in this field.

Defects in solids play a vital role on thermoelectric properties through the direct impacts of electronic band structure and electron/phonon transports, which can improve the electronic and thermal properties of a given thermoelectric semiconductor. Defects in semiconductors can be divided into four different types depending on their geometric dimensions, and thus understanding the effects on thermoelectric properties of each type is of a vital importance. This paper reviews the recent advances in the various thermoelectric semiconductors through defect engineering focusing on the charge carrier and phonon behaviors. First, we clarify and summarize each type of defects in thermoelectric semiconductors. Then, we review the recent achievements in thermoelectric properties by applying defect engineering when introducing defects into semiconductor lattices. This paper ends with a brief discussion on the challenges and future directions of defect engineering in the thermoelectric field.

Thermoelectric (TE) heating and cooling devices, which are able to directly convert thermal energy into electrical energy and vice versa, are effective and have exhibited a potential for energy harvesting. With the increasing consumer demands for various wearable electronics, organic-based TE composite materials offer a promise for the TE devices applications. Conductive polymers are widely used as flexible TE materials replacing inorganic materials due to their flexibility, low thermal conductivity, mechanical flexibility, ease of processing, and low cost. In this review, we briefly introduce the latest research trends in the flexible TE technology and provide a comprehensive summary of specific conductive polymer-based TE material fabrication technologies. We also summarize the manufacture for high-efficiency TE composites through the complexation of a conductive polymer matrix/inorganic TE filler. We believe that this review will inspire further research to improve the TE performance of conductive polymers.

Recent advancement of Internet of Things (IoT) and energy harvesting technology enable realization of flexible thermoelectric energy harvester (f-TEH), with technological prowess for use in biomedical monitoring system integrated applications. To expand a flexible thermoelectric energy harvesting platform, the f-TEH must be required for optimized flexible thermoelectric materials and device structure. In response to these demands related to thermoelectric energy harvesting, many research groups have investigated various f-TEHs applied as a power source for wearable electronics. As a key member of the f-TEH, film-based f-TEHs possess significant applicability in research to realize self-powered wearable electronics, owing to their excellent flexibility, low thermal conductivity, and convenient fabrication process. Thus, based on the rapid growth of thermoelectric film technology, this review aims to overview comprehensively the f-TEH made of various inorganic/organic thermoelectric materials including developed fabrication methods, high thermoelectric performance, and wide-range applications.

Power factor improvement at high temperatures has been a major research topic for the development of skutterudite thermoelectric materials. Here, we attempted to optimize the process parameters for manufacturing skutterudite materials, especially for p-type systems. We focused on the effect of aging time variation to maximize the hightemperature performance of the Ce-filled Fe₃CoSb₁₂ skutterudite system. The optimized aging time was concluded to be a key parameter for the formation of single-phase nanostructures in this p-type skutterudite system. The optimized condition was effective in reducing the bipolar effect at high temperature ranges by increasing the carrier concentration in the p-type system. To confirm the conclusions, the electrical conductivity, Seebeck coefficient, and power factor were measured. The results matched well with the microstructure and with those of an XRD analysis performed for the system.

Thermoelectric Bi2Te3 thin films were synthesized by a co-sputtering method at 300℃. A Fe dopant was considered to enhance the thermoelectric properties of the system. The Seebeck coefficient of the Fe-doped films increased whereas the electrical conductivity decreased. As a result, the power factor of the system increased owing to the enhanced Seebeck coefficient. Grain growth inhibition was detected in the Fe-doped system, which produced more grain boundaries in the Fe-doped films than in the undoped system. The increased grain boundary scattering was deemed to be effective for a reduced thermal conductivity. This is advantageous for the preparation of high-performance thermoelectric films.

In this study, we investigate the effect of an Sb-deficiency on the thermoelectric properties of double-filled n-type skutterudite (In_0.05Yb_0.15Co₄Sb_12-x). Samples were prepared by encapsulated induction melting, consecutive long-time annealing, and finally spark plasma sintering processes. The Sb-deficient sample contained a CoSb₂ secondary phase. Both the double-filled n-type skutterudite pristine and Sb-deficient samples showed metallic behavior in electrical conductivity with increasing temperature. The carrier concentration of the Sb-deficient sample decreased compared with that of the pristine sample. Due to a decrease in carrier concentration, the Sb deficient sample showed decreased electrical conductivity and an increased Seebeck coefficient compared with the conductivity and coefficient of the pristine sample. Furthermore, the Sb deficient sample showed an increase in the power factor (σ·S²); the power factor maximum shifted to athe lower temperature side than ones of the pristine sample. As a result, the Sb-deficient sample represents an improved average figure of merit (ZT) and a ZT_max temperature lower than that of the pristine sample. Therefore, we propose that Sb-deficient double-filled n-type skutterudite thermoelectric material (In_0.05Yb_0.15Co₄Sb_12-x) be used in the 573~673 K temperature range.

We researched about a bulk metallic glass system as an additive to an Ag paste for high temperature thermoelectric modules. Bulk metallic glass (BMG) ribbons were produced by using a rapid solidification process (RSP) under a cooling rate condition higher than 10℃/sec. We investigated BMG characteristics of the ribbons by means of x-ray diffraction (XRD) and differential scanning calorimetry (DSC) in order to evaluate the glass transition temperature (Tg) and the recrystallization temperature (Tx) lower than 400℃. A milling process was also developed to apply the BMG ribbons to a commercial Al paste as an additive for lower sintering temperature.

Bi₂Te₃-based alloys have been intensively investigated as active materials for thermoelectric power generation devices from low-temperature (< 250℃) waste heat. In the present study, we fabricated Pb-doped, p-type Bi_0.48Sb_1.52Te₃ polycrystalline bulks by using meltsolidification and spark plasma sintering techniques, and evaluated their thermoelectric transport properties in an effort to develop optimized composition for low-temperature power generation applications. The electronic and thermal transport properties of Bi_0.48Sb_1.52Te₃ could be manipulated by Pb doping. As a result, the temperature for a peak thermoelectric performance (zT) gradually shifted toward higher temperatures with Pb content, suggesting that thermoelectric power generation efficiency can be enhanced by controlled Pb doping.

Skutterudite materials show PGEC (phonon glass electron crystal) characteristics which is an optimal strategy for designing high performance thermoelectric materials. Now two methods are in parallel to control thermal conductivity of skutterudites, a rattler-atoms doping method and a process for nanostructured bulk materials. Amount of rattler atoms in p-type skutterudite are depends on a Fe/Co ratio of matrix, and the optimal Fe/Co ratio has been reported about from 3:1 to 3.5:0.5 in R(Fe,Co)₄Sb₁₂ structure. In this paper, our discussion for rattler doping research was concentrated on double-rattler systems and DD-doped systems in p-type skutterudites. A melt spinning precess combined with high energy ball milling were suggested as a strategy for nanostructured bulk materials with PGEC (phonon glass electron crystal) characteristics in p-type skutterudites.

The effects of Al-substitution on thermoelectric and charge transport properties of BiCuOSe compounds were investigated. The compounds were prepared by a solid-state reaction and consolidated by SPS (spark plasma sintering). In spite of the increase in the hole concentration with increasing Al amounts in BiCuOSe compound, the electrical conductivity at room temperature was kept constant due to the reduction of mobility. However, electrical conductivities of Al-substituted BiCuOSe compounds at elevated temperature (> 600 K) were higher than those of BiCuOSe, and this result was discussed in terms of it``s the band gap energy. The Seebeck coefficient was drastically reduced when Al was substituted in Bi site, which indicated that the electronic structure was influenced by the Al-substitution into Bi-site.

In this study, we investigate the effect of high-energy ball milling on thermoelectric transport properties in double-filled CoSb3 skutterudite (In0.2Yb0.1Co4Sb12). In0.2Yb0.1Co4Sb12 powders are milled using high-energy ball milling for different periods of time (0, 5, 10, and 20 min), and the milled powders are consolidated into bulk samples by spark plasma sintering. Microstructure analysis shows that the high-energy ball milled bulk samples are composed of nano- and micro-grains. Because the filling fractions are reduced in the bulk samples due to the kinetic energy of the high-energy ball milling, the carrier concentration of the bulk samples decreases with the ball milling time. Furthermore, the mobility of the bulk samples also decreases with the ball milling time due to enhanced grain boundary scattering of electrons. Reduction of electrical conductivity by ball milling has a decisive effect on thermoelectric transport in the bulk samples, power factor decreases with the ball milling time.

In this study, we propose a novel fabrication of an oxide-based lateral thermoelectric pn couple and investigate the characteristics of the thermoelectric couple. Electrospun ZnO and LaSrCoO3 nanofibers are used as n- and p-legs of the couple, respectively. The Seebeck coefficients of the n- and p-type nanofibers and the pn couple are -98.1 μV/K, 42.4 μV/K, and 118.8 μV/K, respectively. The thermoelectric couple generates an output voltage of 484.7 μV at a temperature difference of 4.1 K.

In this study, we fabricated a thermoelectric module made of nanoparticles (NPs) and glass fibers investigated its thermoelectric characteristics. P-type HgTe and n-type HgSe NPs synthesized by colloidal method were used as thermoelectric materials and glass fibers were used as spacers between the hot and cold electrodes of the thermoelectric module. In the module, the average Seebeck coefficients of the HgTe and HgSe NPs were 1260 and -628 μV/K, respectively. The p-n module generated about a voltage of 11.9 mV and showed a power density of 1.6×10-5 μW/cm2 at a temperature difference of 7.5 K.

Thermoelectric materials have been the topic of intensive research due to their unique dual capability of directly converting heat into electricity or electrical power into cooling or heating. Bismuth telluride (Bi2Te3) is the best-known commercially used thermoelectric material in the bulk form for cooling and power generation applications In this work we focus on the large scale synthesis of nanostructured undoped bulk nanostructured Bi2Te3 materials by employing a novel bottom-up solution-based chemical approach. Spark plasma sintering has been employed for compaction and sintering of Bi2Te3 nanopowders, resulting in relative density of g·cm-3 while preserving the nanostructure. The average grain size of the final compacts was obtained as 200 nm after sintering. An improved NS bulkundoped Bi2Te3 is achieved with sintered at 400℃ for 4 min holding time.

Thermoelectric bismuth telluride (Bi2Te3) films were deposited on 4° off oriented (001) GaAs substrates using a modified metal organic chemical vapor deposition (MOCVD) system. The effects of substrate temperature on surface morphologies, crystallinity, electrical properties and thermoelctric properties were investigated. Two dimensional growth mode (2D) was observed at substrate temperature lower than 400℃. However, three dimensional growth mode (3D) was observed at substrate temperature higher than 400℃. Change of growth mechanism from 2D to 3D was confirmed with environmental scanning electron microscope (E-SEM) and X-ray diffraction analysis. Seebeck coefficients of all samples have negative values. This result indicates that Bi2Te3 films grown by modified MOCVD are n-type. The maximum value of Seebeck coefficient was -225 μV/K and the power factor was 1.86×10-3 W/mK2 at the substrate temperature of 400℃. Bi2Te3 films deposited using modified MOCVD can be used to fabricate high-performance thermoelectric devices.