Peak Power Factor Research Articles

Achieving Efficient p-Type Organic Thermoelectrics by Modulation of Acceptor Unit in Photovoltaic π-Conjugated Copolymers.

π‐Conjugated donor (D)−acceptor (A) copolymers have been extensively studied as organic photovoltaic (OPV) donors yet remain largely unexplored in organic thermoelectrics (OTEs) despite their outstanding mechanical bendability, solution processability and flexible molecular design. Importantly, they feature high Seebeck coefficient (S) that are desirable in room‐temperature wearable application scenarios under small temperature gradients. In this work, the authors have systematically investigated a series of D−A semiconducting copolymers possessing various electron‐deficient A‐units (e.g., BDD, TT, DPP) towards efficient OTEs. Upon p‐type ferric chloride (FeCl3) doping, the relationship between the thermoelectric characteristics and the electron‐withdrawing ability of A‐unit is largely elucidated. It is revealed that a strong D−A nature tends to induce an energetic disorder along the π‐backbone, leading to an enlarged separation of the transport and Fermi levels, and consequently an increase of S. Meanwhile, the highly electron‐deficient A‐unit would impair electron transfer from D‐unit to p‐type dopants, thus decreasing the doping efficiency and electrical conductivity (σ). Ultimately, the peak power factor (PF) at room‐temperature is obtained as high as 105.5 µW m−1 K−2 with an outstanding S of 247 µV K−1 in a paradigm OPV donor PBDB‐T, which holds great potential in wearable electronics driven by a small temperature gradient.

First-principle predictions of the electric and thermal transport performance on high-temperature thermoelectric semiconductor MnTe2

Antiferromagnetic pyrite compound MnTe2 is a newly discovered high-performance thermoelectric material. However, its electric and thermal transport performance remained unexplored so far. In this work, the first-principle calculations based on the density functional theory were applied to predict the electric and thermal transport performance of MnTe2. The band structures showed that Te atoms dominate the band energies near the fermi level. The calculated electric transport performance of MnTe2 from BoltzTraP2 package showed that n-type MnTe2 possesses a higher power factor than that of p-type in the carrier concentration range from 1019 to 1021 cm−3. The peak power factor with electronic relaxation time of n-type MnTe2 at 800 K is 3.05 × 1015 μW K−2 cm−1 s−1 at a lower carrier concentration of 0.78 × 1021 cm−3 while p-type is 2.18 × 1015 μW K−2 cm−1 s−1 at a higher carrier concentration of 1.35 × 1021 cm−3. It suggests that high-performance n-type doped MnTe2 is easier to be obtained experimentally. Due to the low average phonon velocity of 2064 m·s−1, MnTe2 has a low lattice thermal conductivity of 0.72 W m−1 K−1 at 800 K. The calculated charged point defect formation energy of several possible n-type doping elements showed that Y or La substituting Mn atom and Cl or Br substituting Te atom are the most possible n-type doping point defects. Combined with the optimal carrier concentration of 0.78 × 1021 cm−3 at 800 K, stoichiometric A0.07Mn0.93Te2 (A = Y, La) and MnTe1.93B0.07 (B = Cl, Br) are expected to possess high thermoelectric properties reaching the theoretical peak power factor with electronic relaxation time of 3.05 × 1015 μW K−2 cm−1 s−1 and the lattice thermal conductivity of 0.72 W m−1 K−1.

Evaluation on the Thermoelectric Cooling Ability of PbTe

High thermoelectric cooling efficiency requires a high average ZT value, especially in a low temperature range. PbTe-based compounds are typical intermediate-temperature thermoelectric materials due to their relatively low ZT values near room temperature. Here, we attempt to enhance the average ZT value of PbTe, especially at 300–600 K, through decreasing its band gap so as to evaluate the thermoelectric cooling performance. The results show that Sn alloying in PbTe can narrow its band gap from ∼0.28 to ∼0.18 eV, which shifts its peak power factor from 673 to 523 K. Combining the enhanced power factor with the reduced lattice thermal conductivity after Sn alloying, a maximum average ZT value of ∼0.74 is obtained in n-type Pb0.785Sn0.2Sb0.015Te at 300–723 K. Finally, the thermoelectric cooling performance of a Pb0.785Sn0.2Sb0.015Te-based single leg is measured, and a cooling ΔTmax of ∼15 K is realized. These results demonstrate that, after tuning the band gap, PbTe can also exhibit promising cooling performance even though it is a typical intermediate-temperature thermoelectric material.

High performance wearable thermoelectric generators using Ag2Se films with large carrier mobility

Flexible thermoelectric generators are suitable for powering wearable electronic devices. In this work, single-phase AgxSe (x = 1.6, 1.8, 2.0, and 2.2) films were successfully deposited on the polyimide substrate by thermal evaporation. An extraordinary high electron mobility was achieved in the ab-plane of Ag1.8Se film because of the highly orientation and crystallization, as well as the lowered effective mass, leading to a high room-temperature power factor of ~17 μW cm−1 K−2 and a peak power factor of ~19 μW cm−1 K−2 at 380 K. A 4-leg flexible thermoelectric generator composed of the Ag1.8Se film demonstrates a maximum power density of 46.8 W m−2 working at the temperature difference of 50 K, and a robust mechanical property with negligible change in the device resistivity upon 1000 times bending. An output voltage of 3.5 mV and an output power of about 2.3 nW were obtained as dressed on the arm.

Very high thermoelectric power factor near magic angle in twisted bilayer graphene

Recent research on twisted bilayer graphene (TBG) uncovered that its twist-angle-dependent electronic structure leads to a host of unique properties, such as superconductivity, correlated insulating states, and magnetism. The flat bands that emerge at low twist angles in TBG result in sharp features in the electronic density of states, affecting transport. Here we show that they lead to superior and tuneable thermoelectric (TE) performance. Combining an iterative Boltzmann transport equation solver and electronic structure from an exact continuum model, we calculate TE transport properties of TBG at different twist angles, carrier densities, and temperatures. Our simulations show the room-temperature TE power factor (PF) in TBG reaches 40 mW m−1 K−2, significantly higher than single-layer graphene and among the highest reported to date. The peak PF is observed near the magic angle, at a twist angle of ≈1.3∘, and near complete band filling. We elucidate that its dependence is driven by two opposing forces: the band gap between the flat and remote bands suppresses bipolar transport and improves the Seebeck coefficient but the gap decreases with twist angle; on the other hand, the Fermi velocity, which impacts conductivity, is smallest at the magic angle and rises with twist angle. We observed a further increase in the PF of TBG with decreasing temperature. The strong TE performance, along with the ability to fine-tune transport using twist angle, makes TBG an interesting candidate for future research and applications in energy conversion and thermal sensing and management.

Controlled Morphology and Its Effects on the Thermoelectric Properties of SnSe2 Thin Films

In the last few years, the thermoelectric properties of tin selenide (SnSe) have been explored in much detail due to its high efficiency and green nature, being free of Te and Pb. In the same chalcogenide family, SnSe2 is also a layered structured material, but its thermoelectric potential has not been widely explored experimentally. Since SnSe2 has the layered structure, its electrical transport properties may strongly be affected by its microstructure and morphology. Here, we report the effect of reaction time on the structure, phase, and morphology of the SnSe2 during solvothermal synthesis process. We have studied four SnSe2 samples with different reaction times. The sample obtained after 16 h of reaction time was named as M1, for 20 h M2, similarly for 24 h was M3 and for 48 hours’ time, the sample was named as M4. We investigated its thermoelectric properties and found that phase purity and morphology can affect the thermoelectric performance of the synthesized samples. The peak power factor (PF) value along the ab plane was (0.69 μWcm−1K−2) for the M4 sample at 575 K, which was the highest among all the measured samples. The comparatively larger PF value of sample M4 can be related to the increase in its electrical conductivity due to increase in phase purity and band gap reduction.

Contrasting Cu Roles Lead to High Ranged Thermoelectric Performance of PbS

AbstractTo obtain high‐performance PbS‐based thermoelectric materials, this study introduces Cu with different contrasting roles in p‐type PbS, which can effectively decrease the lattice thermal conductivity and simultaneously optimize the electrical transport properties. Experimental results illustrate that Cu substitutions and Cu interstitials can improve carrier mobility through lowering effective mass (m*) and carrier concentration (nH) in a low temperature range (300–450 K), and further optimize temperature‐dependent nH in a high temperature range (450–823 K). Both decreased m* and nH shift the peak power factor to low temperature range, leading to an ultrahigh power factor ≈23 µW cm−1 K−2 at 423 K for Pb0.99Cu0.01S‐0.01Cu. Additionally, the special dynamic‐doping behaviors of Cu can continuously promote nH to approach the temperature‐dependent relationship of (nH, opt) ≈ (m*T)1.5, which brings about an eminent average power factor (PFave) ≈ 18 µW cm−1 K−2 among 300–823 K in Pb0.99Cu0.01S‐0.01Cu. Furthermore, the microstructure characterizations unclose that the atomic and nanoscale Cu‐containing defects can effectively intensify the phonon scattering and suppress the lattice thermal conductivity. Consequently, both high ZT (≈0.2 at 300 K) and peak ZT (≈1.2 at 773 K) result in a record‐high average ZT (ZTave) of ≈0.79 at 300–823 K for Pb0.99Cu0.01S‐0.01Cu.

Effects of NbCl5-doping on the thermoelectric properties of polycrystalline Bi2S3

Bi2S3 is considered a potential thermoelectric material owing to its non-toxic and earth-abundant components and intrinsically low thermal conductivity. However, owing to its low electrical conductivity and the coupling relationship between the electric transport properties and thermal transport properties, achieving a high ZT value for polycrystalline Bi2S3 is a major challenge. In this work, a high-valence halogen compound, NbCl5, was employed to enhance the thermoelectric properties of polycrystalline Bi2S3 fabricated by the melting method combined with the spark plasma sintering technique. The enhanced electrical conductivity of polycrystalline Bi2S3 is derived from the increased carrier concentration, which is caused by the substitution of Nb and Cl ions into Bi and S sites, respectively. A peak power factor of 363 μWm−1K‒2 was obtained for Bi2S3 with 1.0 ​wt% NbCl5 doping at 623 ​K. Finally, a maximum ZT of ~0.28, which is approximately four times higher than that of the pristine Bi2S3 sample, was obtained. This work proves that NbCl5 is an effective n-type dopant for the Bi2S3 system, and indicates that high thermoelectric performance can be realized for Bi2S3 with environmentally friendly and low-cost elements.

Low temperature CVD of thermoelectric SnTe thin films from the single source precursor, [nBu3Sn(TenBu)

This work has demonstrated that the single source precursor [nBu3Sn(TenBu)], bearing n-butyl groups and containing the necessary 1 : 1 Sn : Te ratio, facilitates growth of continuous, stoichiometric SnTe thin films. This single source CVD precursor allows film growth at significantly lower temperatures (355-434 °C at 0.01-0.05 Torr) than required for CVD from SnTe powder. This could be advantageous for controlling the surface states in topological insulators. The temperature-dependent thermoelectric performance of these films has been determined, revealing them to be p-type semiconductors with peak Seebeck coefficient and power factor values of 78 μV K-1 and 8.3 μW K-2 cm-1, respectively, at 615 K; comparing favourably with data from bulk SnTe. Further, we have demonstrated that the precursor facilitates area selective growth of SnTe onto the TiN regions of SiO2/TiN patterned substrates, which is expected to be beneficial for the fabrication of micro-thermoelectric generators.

High-Performance Flexible Bismuth Telluride Thin Film from Solution Processed Colloidal Nanoplates.

Thermoelectric generators are an environmentally friendly and reliable solid-state energy conversion technology. Flexible and low-cost thermoelectric generators are especially suited to power flexible electronics and sensors using body heat or other ambient heat sources. Bismuth telluride based thermoelectric materials exhibit their best performance near room temperature making them an ideal candidate to power wearable electronics and sensors using body heat. In this report Bi2Te3 thin films are deposited on a flexible polyimide substrate using low-cost and scalable manufacturing methods. The synthesized Bi2Te3 nanocrystals have a thickness of 35 ± 15 nm and a lateral dimension of 692 ± 186 nm. Thin films fabricated from these nanocrystals exhibit a peak power factor of 0.35 mW/m·K2 at 433 K, which is among the highest reported values for flexible thermoelectric films. In order to evaluate the flexibility of the thin films, static and dynamic bending tests were performed while monitoring the change in electrical resistivity. After 1000 bending cycles over a 50mm ROC, the change in electrical resistance of the film was 23%. Using our Bi2Te3 solutions, we demonstrated the ability to print thermoelectric thin films with an aerosol jet printer, highlighting the potential of additive manufacturing techniques for fabricating flexible thermoelectric generators.

Demand-Side Management of Solar Microgrid Operation: Effect of Time-of-Use Pricing and Incentives

Over 17% of the world’s population lack access to electricity, the majority being in rural areas of sub-Saharan Africa and South Asia. Microgrid technologies are a promising solution towards rural and remote area electrification; however, ever-increasing electricity demand remains a big challenge leading to pronounced power outages. Demand-side management is an indispensable tool towards addressing the challenges. This paper employs a mathematical model based on incentives and time-of-use rates to simulate daily power usage pattern of residential customers using data collected from an isolated village Ngurdoto solar microgrid, Arusha, Tanzania. Customer responsiveness on the increase in price was evaluated based on the concept of price elasticity of demand. Using two demand response strategies, namely, load shifting (LS) and scheduled load reduction (SLR), the results reveal that LS can achieve up to 4.87% energy-saving, 19.23% cost-saving, and about 31% and 19% peak reduction and power factor improvement, respectively. SLR method resulted in about 19% energy-saving, 49% cost-saving, and 24% power factor improvement. Thus, the results presented in this study may lead to a more efficient and stable system than the current state in developing countries’ utility.

Full Thermoelectric Characterization of Stoichiometric Electrodeposited Thin Film Tin Selenide (SnSe).

Tin selenide (SnSe) has attracted much attention in the thermoelectric community since the discovery of the record figure of merit (ZT) of 2.6 in single crystal tin selenide in 2014. There have been many reports since of the thermoelectric characterization of SnSe synthesized or manufactured by several methods, but so far none of these have concerned the electrodeposition of SnSe. In this work, stoichiometric SnSe was successfully electrodeposited at -0.50 V vs SCE as shown by EDX, XPS, UPS, and XRD. The full ZT of the electrodeposits were then measured. This was done by both a delamination technique to measure the Seebeck coefficient and electrical conductivity which showed a peak power factor of 4.2 and 5.8 μW m-1 K-2 for the as deposited and heat-treated films, respectively. A novel modified transient 3ω method was used to measure the thermal conductivity of the deposited films on the deposition substrate. This revealed the thermal conductivity to be similar to the ultralow thermal conductivity of single crystal SnSe, with a value of 0.34 W m-1 K-1 being observed at 313 K.

Band Sharpening and Band Alignment Enable High Quality Factor to Enhance Thermoelectric Performance in n-Type PbS.

Low-cost and earth-abundant PbS-based thermoelectrics are expected to be an alternative for PbTe, and have attracted extensive attentions from thermoelectric community. Herein, a maximum ZT (ZTmax) ≈ 1.3 at 923 K in n-type PbS is obtained through synergistically optimizing quality factor with Sn alloying and PbTe phase incorporation. It is found that Sn alloying in PbS can sharpen the conduction band shape to balance the contradictory interrelationship between carrier mobility and effective mass, accordingly, a peak power factor of ∼19.8 μWcm-1K-2 is achieved. Besides band sharpening, Sn alloying can also narrow the band gap of PbS so as to make the conduction band position between Pb0.94Sn0.06S and PbTe well aligned, which can benefit high carrier mobility. Therefore, incorporating the PbTe phase into the Pb0.94Sn0.06S matrix can not only favorably maintain the carrier mobility at ∼150 cm2V-1s-1 but also suppress the lattice thermal conductivity to ∼0.61 Wm-1K-1 in Pb0.94Sn0.06S-8%PbTe, which contributes to a largely enhanced quality factor. Consequently, an average ZT (ZTave) ≈ 0.72 in 300-923 K is achieved in Pb0.94Sn0.06S-8%PbTe that outperforms other n-type PbS-based thermoelectric materials.

Impact of the scattering physics on the power factor of complex thermoelectric materials

We assess the impact of the scattering physics assumptions on the thermoelectric properties of five Co-based p-type half-Heusler alloys by considering full energy-dependent scattering times vs the commonly employed constant scattering time. For this, we employ density functional theory band structures and a full numerical scheme that uses Fermi's golden rule to extract the momentum relaxation times of each state at every energy, momentum, and band. We consider electron-phonon scattering (acoustic and optical), as well as ionized impurity scattering, and evaluate the qualitative and quantitative differences in the power factors of the materials compared to the case where the constant scattering time is employed. We show that the thermoelectric power factors extracted from the two different methods differ in terms of (i) their ranking between materials, (ii) the carrier density where the peak power factor appears, and (iii) their trends with temperature. We further show that the constant relaxation time approximation smoothens out the richness in the band structure features, thus limiting the possibilities of exploring this richness for material design and optimization. These details are more properly captured under full energy/momentum-dependent scattering time considerations. Finally, by mapping the conductivities extracted within the two schemes, we provide appropriate density-dependent constant relaxation times that could be employed as a fast first-order approximation for extracting charge transport properties in the half-Heuslers we consider.

Enhanced thermoelectric properties in chimney ladder structured Mn(BxSi1-x)1.75 due to the dual lattice occupation of boron

Due to its abundant, inexpensive, and nontoxic features, higher manganese silicide MnSi1.75 has drawn intensive attention as a promising middle temperature thermoelectric material. In this study, we applied aberration-corrected scanning transmission electron microscopy to characterize its chimney ladder crystal structure and found the particular contrast along the [110] direction, contributed from the enhancement of helical Si layers on Mn layers. Moreover, it is demonstrated that the Seebeck coefficient and electrical conductivity of MnSi1.75 could be simultaneously reinforced via boron doping, giving a peak power factor value of 1.72 mW m−1 K−2 at 723 K for Mn(B0.04Si0.96)1.75. Interestingly, it is indicated that boron would occupy both Si lattice and interstitial sites, resulting in an optimized charge carrier concentration and a reduced lattice thermal conductivity at the same time. A maximum zT value of ∼0.55 at 773 K and a high zTave value of 0.4 from 300 to 823 K were eventually realized in the Mn(B0.04Si0.96)1.75 sample.

Self-Nanostructuring in SrTiO3: A Novel Strategy for Enhancement of Thermoelectric Response in Oxides.

Nanostructuring is recognized as an efficient route for enhancing thermoelectric response. Here, we report a new synthesis strategy for nanostructuring oxide ceramics and demonstrate its effectiveness on an important n-type thermoelectric SrTiO3. Ceramics of Sr0.9La0.1TiO3 with additions of B2O3 were synthesized by the mixed oxide route. Samples were sintered in air followed by annealing in a reducing atmosphere. Crystallographic data from X-ray and electron diffraction showed Pm3̅m cubic symmetry for all the samples. High-resolution transmission electron microscopy (HRTEM) showed the formation of a core-shell type structure within the grains for the annealed ceramics. The cores contain nanosize features comprising pairs of nanosize voids and particles; the feature sizes depend on annealing time. Atomic-resolution, high-angle annular-dark-field imaging and electron energy loss spectroscopy in the scanning transmission electron microscopy (STEM-HAADF-EELS) showed the particles to be rich in Ti and the areas around the voids to contain high concentrations of Ti3+. Additionally, dislocations were observed, with significantly higher densities in the shell areas. The observed dislocations are combined (100) and (110) edge dislocations. The major impact of the core-shell type microstructures, with nanosize inclusions, is the reduction of the thermal conductivity. Sr0.9La0.1TiO3 ceramics containing grain boundary shells of size ≈ 1 μm and inclusions in the core of 60-80 nm exhibit a peak power factor of 1600 μW/m·K2 at 540 K; at 1000 K, they exhibit a low thermal conductivity (2.75 W/m·K) and a power factor of 1050 μW/m·K2 leading to a high of ZT of 0.39 ± 0.03. This is the highest ZT reported so far for Sr0.9La0.1TiO3 based-compositions. This nanostructuring strategy should be readily applicable to other functional oxides.

Desain Inti Reaktor SCWR (Supercritical Water Reactor) Model Teras Silinder (r, z) dengan Bahan Bakar Thorium Hasil Daur Ulang

The Research of the supercritical water reactor (SCWR) core design of the cylindrical core model (r, z) using the SRAC program has been done. The SRAC basic code was PIJ and CITATION. PIJ was used to calculate the fuel level and CITATION was used to calculate the reactor core level. The calculation of the reactor core has been done on the 1/4 cylinder core (r, z) and the geometry of the fuel cell was the cylindrical cell. Reactor fuel material was thorium burned 40 GWd/t and 30 GWd/t. The neutron parameters in this research were fuel enrichment, burn up, reactor core size, reactor core configurations, multiplication factor, and power density distribution. Multiplication factor (k-effective) in this research was 1.000004, which is reactor was in a critical condition. The reactor core in critical condition had the size of radius (r) was 130 cm, height (z) was 270 cm and fuel enrichment 2.8262%. The maximum power density was 130.0808 Watts /cm3 which was located at a radius of 25 cm and 135 cm high. The peak power factor in the radial direction was 1.6063 and the peak power factor in the axial direction was 1.3189.

Manipulation of Ni Interstitials for Realizing Large Power Factor in TiNiSn‐Based Materials

AbstractDefect engineering has been identified as an effective strategy for improving thermoelectric performance by tailoring electron and phonon transport. TiNiSn is unique due to its naturally formed Ni interstitials, where the interstitial atoms enable strong phonon scattering that results in reduced lattice thermal conductivity, although an adverse effect on mobility is inevitable. Rather than pursuing the conventional strategy of strengthening the interstitial scattering to improve the performance of TiNiSn‐based materials, an attempt is made to minimize the atomic disorder in order to enhance the mobility, which in turn favors a higher power factor. The altered bandgap, and electrical and thermal properties demonstrate that the interstitials can be effectively controlled by intentionally reducing the amount of Ni. Benefiting from the manipulation of the interstitials, significantly enhanced mobility is achieved in the Ni‐deficient composition, resulting in peak power factor of ≈50 µW cm−1 K−2, which is comparable to the best n‐type half‐Heusler compounds. Additionally, the well‐designed composition employing Ni interstitial manipulation and heavy‐element doping exhibits peak ZT of ≈0.73, higher than that of all other reported TiNiSn‐based materials. The unique role of interstitials in either electron or phonon transport is emphasized, and further encouragement for engineering thermoelectric properties by manipulating intrinsic disorder, especially in materials with complex structures, is provided.

Fuel Burn-up and Radioactivity Inventory Analysis for New In-core Fuel Management of the RSG-GAS Research Reactor

A new fuel management pattern has been applied to the RSG-GAS Research reactor operation. The new fuel management pattern is done so that the replacement of fuel in every operating cycle is more efficient. The new fuel replacement pattern required various safety analyzes, among others related to the fuel fraction and radioactivity inventory of the RSG-GAS. Both of those are the main elements in dose acceptance analysis for workers and communities around the reactor when the reactor operates both in normal or in abnormal conditions. Fuel burn-up and inventory analysis was performed using ORIGEN2 computer program. Inputs for ORIGEN2 are the fuel mass, the time required for one operating cycle as well as the peak power factor in each fuel in the specified fuel management pattern. The result for the 97th Core configuration (T97) is that the average burn-up fraction of each cycle is 6.79%, and the maximus fuel fraction is 52.36% for Fuel Elemet and 56.52% for Contro Elemet. It is also obtained that the largest and dangerous human inventory activity at the end of cycle (EOC) for Iodine radionuclide group is I-131 for 5.18E+04 Ci, and for the alkali metal radionuclide group Cs-137 of 7.65E+03 Ci.

Achieving higher thermoelectric performance for p-type Cr2Ge2Te6 via optimizing doping

Cr2Ge2Te6-based compounds with a layered structure and high symmetry hold a great promise for thermoelectric applications. Our studies have been committed to improve their electrical properties considering the low power factor of only ∼0.23 mW/mK2 in pristine samples. In this work, various doping contents on the site that has less influence on the charge-conducting band have been investigated to enhance the power factor. The results show that Fe-doping is the most favorable among elements we applied. According to the first-principles calculation, the Fe doping on the Cr site leads to the increment of the density of states around the Fermi level. By tuning the carrier concentration via Fe doping, the peak power factor rises from 0.23 mW/mK2 to 0.37 mW/mK2 and zT rises from 0.3 to 0.4 at 830 K for Cr1.9Fe0.1Ge2Te6 along the pressing direction. These results shed lights for designing high performance thermoelectric materials.