High Power Factor Research Articles

Compositing effects for high thermoelectric properties of n-type Bi2S3 via doping C60 nanoparticles

Bi2S3 is one of the most inexpensive and eco-friendly thermoelectric materials in the medium temperature region. In this work, functionalized fullerene (C60) was successfully doped into Bi2S3 to optimize its thermoelectric properties by a simple hydrothermal method. Guided by first-principles calculations for compositional design, electron band structure of Bi2S3/C60 nanocomposites is reduced. Additionally, the high modulus elasticity of C60 further increases phonon scattering in Bi2S3. Due to composite effects synergistically optimized the transports of electron and phonon by C60 nanoparticles in Bi2S3-based materials, the electrical and thermal conductivity of Bi2S3-based nanocomposites are optimized and decreased to varying degrees, respectively. The highest power factor (PF) of Bi2S3/C60 nanocomposites is up to 181μW·m-1·K-2, and the lowest thermal conductivity is 0.17W m-1·K-2. Ultimately, the ZT value of Bi2S3/C60 (10ml) nanocomposites reached 0.38, nearly a threefold improvement over the pure Bi2S3, which further expands the application range of Bi2S3-based thermoelectric materials.

Enhancing power quality in wireless DC power supplies through active power filtering: A computer simulation approach

This paper presents a computer simulation model for a high-power factor wireless DC power supply system, integrating an active power filter (APF) at the rectifier stage on the transmitter side using a rectifier boost technique. The APF, employing a MOSFET switch regulated by active pulse width modulation (APWM) within a current control loop, addresses pulsating and distorted AC supply currents caused by non-linear loads. A robust closed-loop control mechanism, including a subtractor circuit, proportional-integral (PI) controller, and comparator, ensures the generation of a continuous sinusoidal waveform synchronized with the supply voltage. The model utilizes a high-frequency inverter to convert DC to AC, which is then wirelessly transmitted via wireless power transfer (WPT) technology and converted back to DC by a high-frequency rectifier. MATLAB/Simulink simulation results show a significant reduction in total harmonic distortion (THD) of the AC supply current, complying with IEEE 519 standards. Selected results are presented to verify the proposed method's effectiveness in reducing harmonic distortions and enhancing power quality. This study highlights the advantages of WPT in scenarios where traditional wired connections are impractical and underscores the potential of this system for real-world applications, particularly in developing high-power factor wireless DC power supply systems.

Investigations of optoelectronic, magnetic, and transport properties of Zintl-phosphides BaX2P2 (X=Cd, Sn, Cu) for green technology: First principle calculations

One way to decarbonize the world's energy generation is through thin-film photovoltaics (PV), there are significant problems with elemental abundance, stability, or performance with the thin-film solar absorbers that are now on the market. We present the optoelectronic and transport properties of Zintl-phosphides BaX2P2 (X = Cd, Sn, Cu) using first-principles calculations based on density functional theory. Our calculations show that increasing the band gap of Cd/Sn and Cu-based phosphides from 0.5 to 4.0 eV enables fine adjustment of bandgaps, structure, and optoelectronics, broadening the material's potential applications in the semiconducting industry. Strong absorption occurs in the energy range of 4–8 eV; it concluded that their optical characteristics, such as natural and imaginary dielectric functions, refractive index, and absorption coefficient, might make them useful in optoelectronic and photovoltaic applications. In the 50–800 K temperature range, power factor (PF), electrical conductivity, thermal conductivity, and Seebeck coefficient were investigated. With PFs of approximately 7.5 × 1010 W/K2ms, respectively, the compound demonstrated a considerable potential utility in thermoelectric devices. An assessment of radiation shielding performance was conducted using the XCOM tool across a broad energy range ranging from 15 keV to 15 MeV. The findings indicated that the mass attenuation coefficient (GMAC) values increased proportionately of BaCd2P2, BaSn2P2, and BaCu2P2 samples. The GMAC peaked for all sample compositions at around 0.015 MeV, with values spanning from 42.94 cm2/g for BaCd2P2 to 51.96 cm2/g for BaCu2P2. Nevertheless, when elevating the energy level beyond 15 keV, a notable decline in GMAC values was observed. This is likely mostly attributable to the predominance of photoelectric interactions at lower energy levels. These compounds' strong absorption patterns and high PF make them promising materials for thermoelectric and photovoltaic applications.

Carbon monochalcogenides/graphene van der Waals heterostructures for sustainable energy harvesting

We constructed the van der Waals (vdW) heterostructures by stacking graphene (G) on top of carbon-based monochalcogenides (CX; X = S, Se, and Te) monolayer in two different patterns (I and II) and predicted various physical properties through first-principles calculations. Among the six heterostructures, three systems (CS/G in Pattern-I and II, and CSe/G in Pattern-II) were found to be most stable. Additionally, the calculated electronic properties confirmed that the CS/G and CSe/G heterostructures in Pattern II are indirect semiconductors with narrow band gap values of 0.49 and 0.30 eV, respectively. Notably, both heterostructures (CS/G and CSe/G) exhibit significantly larger electron carrier mobilities of 762.83 and 206.84 m2/Vs at room temperature, respectively. Furthermore, intrinsic and interface dipoles in both heterostructures were found to align along the +z axis, enhancing charge transfer at the interface and narrowing the band gap, particularly in CSe/G. This polarization effect contributes to the observed high electron mobility and thermoelectric performance. Electronic transport coefficients like the Seebeck coefficient, electrical conductivity, and thermoelectric power factor are predicted using the Boltzmann transport theory implemented in the BoltzTrap code. The highest power factor 249mW/mK2 was achieved for the CSe/G heterostructure at 300K, demonstrating its ability for good thermoelectric purposes. Besides, the computed optical properties revealed the potential of the CS/G heterostructure as a light absorber with an excellent solar light energy conversion efficiency (η) of 23.57 % for solar cell device applications. Our predictions show that the novel 2D CX/G vdW heterostructures could be promising candidates for designing new solar and heat energy harvesting devices.

Synergetic Optimization via Indium and Rare Metal Yttrium Co-doping in GeTe Results in High Power Factor and Excellent Thermal Performance.

Excess intrinsic Ge vacancies in GeTe materials lead to excessively high hole concentration and high thermal conductivity, producing poor thermoelectric performance. Here, synergistic control and optimization of the thermoelectric transport properties and microstructure of GeTe-based materials were achieved through co-doping with In and rare earth element Y, resulting in a significant enhancement of thermoelectric performance. The Ge0.94In0.03Y0.03Te sample reached a ZTmax of 1.84 at 773 K, representing an increase of around 91% compared to the GeTe matrix. The experimental results indicate that the doping of In optimizes the band structure by introducing resonant levels and increasing the degeneracy of the valence band. Y doping introduces in situ nanoscale secondary phases and lattice distortions due to defect generation, enhancing phonon scattering and significantly reducing the κlat. This work elaborates on how co-doping with In and Y achieves the optimization of the thermoelectric performance of GeTe-based materials. While the electrical transmission characteristics are improved, the thermal conductivity is significantly reduced. For the Ge0.94In0.03Y0.03Te sample, κlat decreased to ∼0.56 W m-1 K-1 at 573 K, resulting in a ZTave of ∼0.99 over the entire temperature range, representing over 140% improvement compared to undoped GeTe. This improvement is significantly higher compared with other works on GeTe and PbTe.

Development of graphene/MWCNT/Ag2Se hybrid thermoelectric materials with different concentrations of PEDOT:PSS for low-temperature applications

Studies in low-temperature applications in the fields of medicine and wearable technologies are limited to thermoelectric works with commercial poly(3,4-ethylenedioxy-thiophene):polystyrenesulfonate (PEDOT:PSS) aqueous solutions. Unlike other studies, in this study, the effects of adding graphene, multi-walled carbon nanotube (MWCNT) and silver selenide into PEDOT:PSS at different concentrations in the production of semiconductor polymer inks on the thermoelectric properties were examined using Taguchi analysis. In the examination without adding additives, as the ratio of PEDOT:PSS increased from 1 % to 3 % and 5 %, 2.50 and 4.92 times increase in electrical conductivity and 1.19 and 1.49 times increase in the Seebeck coefficient were observed, respectively. P- and n-type inks were produced in three different concentrations using four different materials. According to the results of the study, to obtain p-type material with good performance, the concentration of PEDOT:PSS in the mixture must be high and the Ag2Se concentration must be low, and also to get a high-performance n-type material, the concentration of Ag2Se must be as high as the homogeneous mixture allows, and PEDOT:PSS concentration must be low. When the highest Power Factor and Figure of Merit results were evaluated, PPp9 was found for p-type material and PPn2 was found for n-type material, and it is considered that these inks are suitable for printing with 3D printing technology.

In-silico realization of YX (X = N, P, As) pnictide monolayers as highly efficient thermoelectric materials

Exploiting the changes in the electronic and vibrational properties accompanying the reduction of dimensionality from 3D to 2D has now become a widely established strategy for developing materials breaking the figure of merit (ZT) ∼ 1 barrier that was experienced in much of the last century. Several studies have suggested the possibility of developing rare earth pnictides into a new family of prospective thermoelectric (TE) materials owing to the strong p-d hybridization in these materials, leading to dispersive band edges and, consequently, high carrier mobilities in these semiconductors. Motivated by the above developments, we explored the electronic and transport properties of three yttrium pnictide monolayers. We present a detailed investigation highlighting the merit of YX (X = N, P, As) monolayer-based materials for TE applications. We found a high power factor for p-type (n-type) YX monolayers in the y-direction (x-direction). This, in conjunction with low to moderate lattice thermal conductivities 3.335, 1.779, and 1.648 Wm-1K-1 of the YN, YP, and YAs monolayers, respectively, at 500 K, leads to high ZTs in optimally doped YN, YAs and YP of 2.02, 1.39, and 1.18. The finding of high TE performance adds further evidence in support of the conjecture that dimensionality reduction in semiconducting materials with strong p-d hybridization can lead to particularly high electrical conductivities (reaches up to 217.84 × 106 Ω-1m-1 for YN), thereby resulting in excellent ZT. The high TE performance of these materials at 500 K suggests the prospect of developing rare-earth-based materials for energy applications.

Grain recovery facilitated low-angle grain boundaries and texture for high-performance BiSbTe alloys

Low-angle grain boundaries (LAGBs) bring an effective scattering of phonons while maintaining a weak effect on charge carrier transport, which could be utilized for enhancing the thermoelectric performance of solid materials. In the Bi2Te3-based materials fabricated by hot extrusion (HE) technique, however, the formation of the LAGBs is evitably accompanied by severe recrystallization, resulting in texture loss and hindering further zT improvement. Here, we demonstrate a feasible strategy utilizing the grain recovery to maintain dense LAGBs with high grain orientation by the optimized HE technique. As a result, a low thermal conductivity of about 1 W m−1 K−1 and a high power factor of 4.2 mW m−1 K−2 are achieved at 300 K for p-type Bi0.5Sb1.5Te3 alloys, leading to a high room-temperature zT of 1.3. Further, with a decent flexural strength of 25.3 MPa, a 23-pair TE cooling module with the dice dimensions of 0.63 × 0.63 × 1.00 mm3 is assembled, which exhibits a maximum temperature difference of 87.8 K at a hot-side temperature Th of 350 K. These results highlight the important role of grain-recovery manipulation in simultaneously optimizing the thermal and electrical properties toward high-performance Bi2Te3-based TE materials.

Enhancing the Thermoelectric Performance of n-Type Mg3Sb2-Based Materials via Ag Doping.

The n-type Mg3(Sb, Bi)2 compounds show great potential for wasted heat energy harvesting due to their promising thermoelectric properties. This work discovers that doping transition element Ag into the n-type Mg3(Sb, Bi)2 can effectively optimize the power factor and suppress the lattice thermal conductivity simultaneously. Interestingly, the Ag doping has different effects compared to the isoelectronic and same group element Cu addition studied previously. A high power factor of 19.6µW cm-1 K-2 is obtained at 673K owing to the increased electrical conductivity. At the same time, the lattice thermal conductivity is reduced to ≈0.5W m-1 K-1 because of enhanced phonon scattering induced by Ag atoms. These improvements lead to a peak figure of merit (ZT) of 1.64 at 673K as well as a high average ZT of 1.27 is obtained from 323 K to 673K. Furthermore, a thermoelectric single leg with a competitive conversion efficiency of ≈11% under a hot-side temperature of 673K is fabricated successfully. In addition, a 2-pair module composed of n-type Mg3(Sb, Bi)2 alloy and p-type MgAgSb-based compound demonstrates the high conversion efficiency of ≈7.9% at a temperature difference of 277K, which will significantly upgrade the sustainable energy recycling technology.

Improving DC power supply performance: insights into Cuk and modified Cuk converters' stability and power factor

Abstract The conversion of alternating current (AC) to direct current (DC) is pivotal for modern electrical systems, significantly influencing power delivery efficiency and stability. As the reliance on DC-powered electronic devices grows, optimizing AC-DC converters becomes increasingly important. Various converter topologies, including buck, boost, buck-boost, Cuk, and SEPIC configurations, exhibit unique characteristics that affect their efficiency and impact on the power grid. This study examines the performance of Cuk and modified Cuk converters, utilizing PSIM software to simulate these converters for a 1.4 kW power supply. The simulations reveal that both the Cuk and modified Cuk converters achieve reduced ripple in voltage and current outputs, addressing a significant concern for DC power supplies. Additionally, the modified Cuk converter demonstrates a marked reduction in the total harmonic distortion (THD) of the source current. This study explored the interaction between converter topologies and varying load conditions, emphasizing their impact on power factor—a measure of electrical power consumption. A higher power factor indicates improved efficiency and reduced reactive power, benefiting both the electrical system and the grid. The research further investigates how load variations affect power factor and converter performance, providing insights into designing converters that enhance system reliability and efficiency. By validating the simulation results with experimental data, it has been established that the modified Cuk converter topology offers superior performance and stability. This advancement supports the development of converters that optimize power factor and energy consumption, which are crucial for advancing electrical infrastructure. By bridging the gap between simulation and real-world performance, this work aims to provide valuable insights that can inform future enhancements in domestic EV charging infrastructure, ultimately contributing to the broader adoption of electric vehicles.

Research on characteristic and DC voltage balancing control of a novel three‐phase line‐voltage cascaded unity power factor rectifier under unbalanced grid

AbstractAccording to the operating modes of three‐phase line‐voltage cascaded boost high power factor rectifier topology, the operating characteristics of the rectified output voltage of each module and the characteristics of the topology for automatically balancing the input current under the unbalanced grid are analyzed in this article. Based on the analysis to the unique feature, a simple dual‐loop PI control strategy in the rotating coordinate system is designed with no need to deal with the negative sequence component of grid voltage. In response to the issue of unbalanced DC‐link capacitor voltage of each module caused by unbalanced grid, injection of the zero‐sequence voltage component is adopted in the designed control system, which make the output power of each module be able to be independently regulated, so that the balancing control to the DC‐link capacitor voltage of each module is realized. At the same time, the three‐phase input currents always remain in balance automatically operating under unity power factor. Simulations and experiments have verified the superiority of the topology structure and the feasibility of the control strategy.

Valence Band Modification and Enhanced Phonon‐Phonon Interactions for High Thermoelectric Performance in GeTe

AbstractThe strong coupling between carrier and phonon transport in thermoelectric (TE) materials severely limits improvements to the figure of merit (ZT). In this work, an approach is proposed to weaken electron‐phonon coupling, effectively enhancing the TE performance of GeTe. Alloying with Zn4Sb3 reduces excessive carrier concentration (nH), widens the bandgap, and promotes band convergence, synergistically improving charge carrier transport and ensuring a high power factor. Additional Pb doping further optimizes nH, boosting the power factor even more. Moreover, phonon transport is suppressed through Pb doping, as reflected in enhanced acoustic‐optical interactions due to the crossing of optical and acoustic modes, and a reduction in sound group velocity. This reinforced strong phonon scattering, combined with multi‐scale hierarchical nano/microstructures in the matrix, significantly reduces lattice thermal conductivity. As a result, a high ZT of 2.1 is achieved at 753 K in Ge0.9Pb0.1Te+0.9%Zn4Sb3. Alongside optimized mechanical performance, a high power density of 1.46 W cm−2 is realized at a temperature difference of 350 K in the fabricated 7‐pair TE module. The findings demonstrate the effectiveness of a stepwise optimization strategy for developing high‐performance TE materials.

Realizing synergistic optimization of electrical and thermal transport properties in BiCuSeO ceramics via multi-element doping

In this study, the design of high-entropy alloys (multi-element substitution, Al3+/La3+/Sb3+/Y3+) was used to increase material entropy and improve heat scattering to further reduce thermal conductivity. Concurrently, Ca2+ ion hole doping was used to improve its electrical conductivity. Therefore, a series of Bi0.92−xAl0.02La0.02Sb0.02Y0.02CaxCuSeO (x = 0, 0.02, 0.06, 0.10, and 0.14) ceramics was prepared using a combination of high-energy ball milling and cold isostatic pressing. The multi-element substitution of Al0.02La0.02Sb0.02Y0.02Ca0.02 in the Bi site resulted in a minimum thermal conductivity of 0.35 Wm−1K−1, which is one-third of that of intrinsic BiCuSeO. Simultaneously, the conductivity increased up to 10–20 times that of intrinsic BiCuSeO, proportional to the amount of Ca2+ doping. Furthermore, the optimum component Bi0.82Al0.02La0.02Sb0.02Y0.02Ca0.10CuSeO exhibited an extremely high power factor of 568.55 μWm−1K−2 at 773 K, significantly higher than that of pure BiCuSeO (148.7 μWm−1K−2). Consequently, a peak ZT value of approximately 1.12 was achieved at 773 K, which was 4.48 times higher than that of the pristine BiCuSeO specimen (approximately 0.25). Our findings provide a novel strategy to optimize the thermoelectric properties of BiCuSeO and other materials.

Chemical Pressure-Induced Unconventional Band Convergence Leads to High Thermoelectric Performance in SnTe.

Band convergence is considered a net benefit to thermoelectric performance as it decouples the density of states effective mass ( ) and carrier mobility (µ) by increasing valley degeneracy. Unlike conventional methods that typically prioritize at the expense of µ, this study theoretically demonstrates an unconventional band convergence strategy to enhance both and µ in SnTe under pressure. Density functional theory calculations reveal that increasing pressure from 0 to 5 GPa moves the Σ-band of SnTe upward, reducing the energy offset between L- and Σ-band from 0.35 to 0.2 eV while preserving the light band feature of the L-band. Consequently, a high power factor (PF) of 119.2 µW cm-1 K-2 at 300 K is achieved for p-type SnTe under 5 GPa. Chemical pressure also induces conduction band convergence, significantly enhancing the PF of n-type SnTe. Additionally, the interplay between pressure-induced phonon modes leads to a moderate increase in lattice thermal conductivity of SnTe below 3 GPa, which combined with the significantly enhanced PF, contributes to a large enhancement in ZT. Consequently, predicted ZT values of 2.12 at 650 K and 2.55 at 850 K are obtained for p- and n-type SnTe, respectively, showcasing substantial performance enhancements.

Investigation of the physical properties and pressure-induced band gap tuning of Sr3ZBr3 (Z=As, Sb) for optoelectronic and thermoelectric applications: A DFT - GGA and mBJ studies

This study discusses the feasibility of diversifying the scope of application of lead-free Sr3ZBr3 (Z = As, Sb) as promising materials for their enhanced electronic, mechanical, optical, thermodynamic, and thermoelectric properties using first-principles calculation based on Density Functional Theory (DFT). Both compounds have cubic crystal structures, and both materials' dynamic stability is validated by the lack of negative frequencies in their phonon dispersion spectra. Besides ground state physical characteristics, we also examined the impact of hydrostatic pressure (0–21 GPa) on electronic, mechanical, and optical properties. The lattice parameters exhibit a linear decrease from 6.27 to 5.61 Å for Sr3AsBr3 and 6.45 to 5.71 Å for Sr3SbBr3 under increasing pressure, attributed to bond length reduction, which alters their physical properties. Initially observed direct band gap (Γ-Γ) of Sr3AsBr3 and Sr3SbBr3 were 2.35 and 2.30 eV using modified Becke-Johnson (mBJ) functional which reduces to 1.15 and 0.82 eV as the compounds go from 0 to 21 GPa pressure. This study reveals enhanced optical properties under pressure, with broader spectral response, increased sensitivity, and improved dielectric constant. Optical absorption and conductivity also shift toward lower-energy photons. The investigation further shows that the compounds show brittle to ductile transition under high pressure. Their ductility and anisotropy nature are further enhanced with pressure along with other mechanical features. The thermodynamic properties indicate their ability to withstand and perform well at high temperatures and pressures. Lastly, the thermoelectric properties of Sr3ZBr3 (Z = As, Sb) were assessed through electrical and thermal conductivity, Seebeck coefficient, power factor (PF), and figure of merit (ZT) as a function of temperature. Both compounds exhibit high PF and near-unity ZT. These findings underscore their potential as strong candidates for optoelectronic and thermoelectric devices, owing to their direct bandgap and exceptional properties.

First principle study of electronic, optoelectronic, and thermoelectric properties of zintl phase alloys BaAg2X2 (X = S, Se, Te) for renewable energy

Novel Zintl phases exhibiting promising thermoelectric properties have garnered considerable traction, largely attributed to the accuracy of computational estimates. In the present investigation, the density functional theory-based WIEN2k code is employed to analyze the structural, optoelectronic, and transport behavior of the BaAg2X2 (X = S, Se, Te) Zintl phase. All these compositions belong to the stable trigonal phase with nominal expansion in the unit cell with the replacement of S with Se and Te. A negative value of enthalpy of formation of −2.30, −2.0, and −1.80 for BaAg2S2, BaAg2Se2, and BaAg2Te2, respectively, assures their thermodynamic stability. These compositions demonstrate dynamic stability, as evidenced by the nonexistence of negative (-ve) frequency values in their phonon spectra. Increasing the size of chalcogens enhances the spin-orbit coupling and reduces the bandgap value from 2.10 to 1.55 eV. The examination of optical response suggests that studied compositions display high absorption and low energy loss in the visible range, rendering them suitable for optoelectronic devices. The temperature-dependent transport behavior is computed using BoltzTrap code, and the RT value of power factor is recorded as 0.89 × 1011, 0.65 × 1011, and 0.54 × 1011 Wm− 1K− 2 for BaAg2X2 (X = S, Se, Te). A high power factor value at elevated temperatures indicates the promising efficacy of studied compositions in thermoelectric device applications.

Optimization of Thermoelectric Performance of Ag2Te Films via a Co-Sputtering Method.

Providing self-powered energy for wearable electronic devices is currently an important research direction in the field of thermoelectric (TE) thin films. In this study, a simple dual-source magnetron sputtering method was used to prepare Ag2Te thin films, which exhibit good TE properties at room temperature, and the growth temperature and subsequent annealing process were optimized to obtain high-quality films. The experimental results show that films grown at a substrate temperature of 280 °C exhibit a high power factor (PF) of ~3.95 μW/cm·K2 at room temperature, which is further improved to 4.79 μW/cm·K2 after optimal annealing treatment, and a highest PF of ~7.85 μW/cm·K2 was observed at 200 °C. Appropriate annealing temperature effectively increases the carrier mobility of the Ag2Te films and adjusts the Ag/Te ratio to make the composition closer to the stoichiometric ratio, thus promoting the enhancement of electrical transport properties. A TE device with five legs was assembled using as-fabricated Ag2Te thin films. With a temperature difference of 40 K, the device was able to generate an output voltage of approximately 14.43 mV and a corresponding power of about 50.52 nW. This work not only prepared a high-performance Ag2Te film but also demonstrated its application prospects in the field of self-powered electronic devices.

Research on the new control strategy of the three-phase VIENNA rectifier

Abstract The VIENNA rectifier has long been used in applications such as charging piles, and the theoretical research on its control strategy is enumerated. Compared with other circuit components, the VIENNA rectifier has fewer power components and a higher power factor, so it is applied to more application scenarios. The traditional PI control has a long start-up response time and a high overshoot, while the sliding mode control (SMC) has excellent control performance for nonlinear systems. In my article, the control mode of the VIENNA rectifier is analyzed mathematically, SMC takes controls of the current inner loop, and a new exponential reaching rate is put forward the at first improve the control process. Finally, a complete system simulation model is built to prove the superiority of the VIENNA rectifier based on an optimized SMC control strategy for each control target and the corresponding control strategy. The results show that the control effect is obviously optimized by using this method.

Data-driven prediction of higher-order structure in carbon nanotube films for high thermoelectric power factor

We optimized the higher-order structures and semiconducting purity of single-walled carbon nanotubes (SWCNTs) to enhance the thermoelectric power factor PF by combining the thermoelectric random stick network (TE-RSN) method and a genetic algorithm. The PF of the optimized films was increased approximately fivefold for initial random structures. In addition, while the random structures showed the maximum PF when the ratio of semiconducting to metallic SWCNTs R s exceeded 0.98, the optimized structures converged to an R s of approximately 0.9. The optimized structures exhibited an increased local density and the peak of alignment angle distribution, leading to an increase in both the electrical conductivity and the Seebeck coefficient. We interpreted the increase in the Seebeck coefficient using a serial model. The results indicated that the reduction in the number of contacts within the paths and the subsequent increase in temperature difference on semiconducting SWCNTs led to the increase in the Seebeck coefficient.

High-performance thermoelectric PEDOT:PSS fiber bundles via rational ionic liquid treatment

Rapid growth of wearable technology generates increasing demand for lightweight and elastic energy harvesting systems. Among them, conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) shows great potential for lightweight and flexible thermoelectric generators. However, the practical applications of PEDOT:PSS have been restricted by the low Seebeck coefficient and power factor. Here, PEDOT:PSS/1,3-dimethylimidazolium dicyanamide (MMIM:DCA) fiber bundles with enhanced thermoelectric performance have been fabricated by optimizing the content of ionic liquids (ILs), and the duration of dual post-treatment with H2SO4 and NaBH4. The as-prepared fiber bundles exhibit a high power factor of 91.8 μW/m K−2 at 298 K. Detailed characterizations confirm that the phase separation and structural rearrangement of the polymer chains triggered by ILs ensure high charge carrier mobility, resulting in increased electrical conductivity. Meanwhile, the strong binding of DCA− to the PEDOT structure, combined with the hydrophilicity and potent reducing effect of MMIM+, synergistically alters the oxidation state of PEDOT, leading to an enhanced Seebeck coefficient. Moreover, the assembled flexible fiber bundle thermoelectric devices exhibit superior performance and usability, which show an output power density of 36.76 μW cm−2 with a temperature gradient of 25 K. This work offers valuable insights into the development of high-performance organic thermoelectric materials via the modulation of polymer chains.