Thermoelectric Seebeck Effect Research Articles

Progress of microscopic thermoelectric effects studied by micro- and nano-thermometric techniques

Heat dissipation is one of the most serious problems in modern integrated electronics with the continuously decreasing devices size. Large portion of the consumed power is inevitably dissipated in the form of waste heat which not only restricts the device energy-efficiency performance itself, but also leads to severe environment problems and energy crisis. Thermoelectric Seebeck effect is a green energy-recycling method, while thermoelectric Peltier effect can be employed for heat management by actively cooling overheated devices, where passive cooling by heat conduction is not sufficiently enough. However, the technological applications of thermoelectricity are limited so far by their very low conversion efficiencies and lack of deep understanding of thermoelectricity in microscopic levels. Probing and managing the thermoelectricity is therefore fundamentally important particularly in nanoscale. In this short review, we will first briefly introduce the microscopic techniques for studying nanoscale thermoelectricity, focusing mainly on scanning thermal microscopy (SThM). SThM is a powerful tool for mapping the lattice heat with nanometer spatial resolution and hence detecting the nanoscale thermal transport and dissipation processes. Then we will review recent experiments utilizing these techniques to investigate thermoelectricity in various nanomaterial systems including both (two-material) heterojunctions and (single-material) homojunctions with tailored Seebeck coefficients, and also spin Seebeck and Peltier effects in magnetic materials. Next, we will provide a perspective on the promising applications of our recently developed Scanning Noise Microscope (SNoiM) for directly probing the non-equilibrium transporting hot charges (instead of lattice heat) in thermoelectric devices. SNoiM together with SThM are expected to be able to provide more complete and comprehensive understanding to the microscopic mechanisms in thermoelectrics. Finally, we make a conclusion and outlook on the future development of microscopic studies in thermoelectrics.

Tight-binding description for the electronic band structure of penta-graphene

We present an efficient parameterized tight-binding (TB) model which can induce the energy bands that are consistent with results from ab-initio calculations. Besides the comparison of our simple TB model to the previous ones, we also supplement further neighbor interactions into the TB Hamiltonian to analyze the band structure and consider the impact of each type of TB parameters such as onsite and hopping energies, overlap terms of wave functions on the shape and the position of the energy bands. Then a set of appropriate parameters is selected to reproduce reasonably important characteristics of the band structure captured by ab-initio calculations, particularly at the low energy region near the Fermi level, which is relevant for many applications. Moreover, the TB model is applied to predict the impact of a vertical electric field on the electronic properties and the thermoelectric Seebeck effect of penta-graphene. It unveils that the bandgap is strongly modulated under the external field and the intrinsic Seebeck coefficient of penta-graphene is found to be 67 times as high as that of graphene.

Operating temperature and temperature gradient effects on the photovoltaic properties of dye sensitized solar cells assembled with thermoelectric–photoelectric coaxial nanofibers

In this work, the coaxial electrospinning technique was used to prepare coaxial nanofibers (CNFs) consisting of N-type thermoelectric Nb doped SrTiO3 (Nb/STO) coated with a thin layer of TiO2, which was referred to simply as TiO2–Nb/STO. Then a certain amount of TiO2–Nb/STO CNFs was added into the TiO2 nanocrystalline layer to obtain the composite photoanode of dye-sensitized solar cells (DSSCs). Owing to the high electrical conductivity and straightforward electron transport channels for TiO2-Nb/STO CNFs, the device assembled with 10 wt% TiO2-Nb/STO CNFs demonstrated the highest power conversion efficiency (PCE) of 7.25%, which was significantly higher than the reference one (6.45%). In order to investigate the temperature gradient (ΔT) on the photovoltaic performances of DSSCs assembled with TiO2-Nb/STO CNFs, a cold source (0 °C) and a heat source (75 °C) was placed on the Pt counter electrode to create a negative ΔT (−7 K) and a positive ΔT (+7 K), respectively. The mechanism model of thermoelectric effect on the charge transfer dynamic process of DSSCs under different ΔT is established and explained. Data showed that in response to temperature fluctuations, the performance of both reference device and 10% device could be affected. The cold source enable the reference device to obtain the highest PCE of 6.75% due to an increase in open-circuit voltage (Voc). This behavior is mainly ascribed to the reduced internal carrier recombination rates, caused by decreased carrier concentrations at low operating temperature. Herein, the operating temperature refers to an average value between the temperatures on both sides of each device. On the contrary, 10% device applying hot source results in an increase of short-circuit current density (Jsc) and fill factor (FF), yielding the highest PCE of 7.61% despite the negative effects of high operating temperature on Voc. It is found that the hot source benefits the fast electron transfer for 10% device under the synergistic effect of thermoelectromotive force and fast charge carrier diffusion. These results further confirm that the improved photovoltaic performance of 10% device under the condition of hot source was primarily attributed to the thermoelectric Seebeck effect of TiO2-Nb/STO CNFs.

Carbonized Waste Cotton/Stearic Acid Composites for Photo-Thermal Conversion and Heat Storage

Photo-thermal conversion is an effective method to utilise solar energy. The generated heat can be converted into electrical energy through the thermoelectric Seebeck effect. However, the key challenge in enhancing solar-thermal-electric conversion is to achieve efficient photo-thermal conversion and temperature difference control. Herein, new composite materials are prepared using abundant and cheap raw materials to simultaneously realise photo-thermal conversion, heat storage, and heat supply for a thermoelectric device. The composites consist of carbonised waste cotton and stearic acid (SA), where carbonised waste cotton can achieve efficient full spectrum photo-thermal conversion and SA can store the generated heat to maintain a stable temperature for a thermoelectric device. The best content of SA is found to be 85 wt-% in the composites due to uniform dispersion and ideal combination. The 3D netlike structure of carbonised waste cotton provides increased heat transfer paths and also prevents leakage of SA during phase change. The maximum phase change enthalpy is 203.6 J g−1 for the composite with 85 wt-% SA, which is almost the same as pure SA, assuring high density heat storage. A light-thermal-electric conversion device is further constructed based on as-prepared composites and a thermoelectric system. The generated electricity can light up a light-emitting diode with strong intensity.

(Invited) Impact of Spark Plasma Sintering on the Thermoelectric Properties of Advanced Nanostructured Materials for Waste Heat Recovery

The rapid development of nanomaterials in the past decade has provided a possibility of directly converting waste heat back to electricity based on the thermoelectric Seebeck effect. In the past four years, we have developed a transformative approach to pioneered low cost and scalable solution-phase growth methods to mass produce thermoelectric nanowires and nanowire heterostructures to match the physical and economic magnitudes of energy use and economical entertainment in the manufacture/recycling. We have studied how spark plasma sintering can help to improve the density, mechanical strength, and electrical conductivity of these nanowires and nanowire heterostructures while minimizing the phase impurity and grain growth. These nanostructured thermoelectric materials show a significantly enhanced performance compared to the bulk crystals based on the quantum confinement and energy filtering.

A review of carrier thermoelectric-transport theory in organic semiconductors.

Carrier thermoelectric-transport theory has recently become of growing interest and numerous thermoelectric-transport models have been proposed for organic semiconductors, due to pressing current issues involving energy production and the environment. The purpose of this review is to provide a theoretical description of the thermoelectric Seebeck effect in organic semiconductors. Special attention is devoted to the carrier concentration, temperature, polaron effect and dipole effect dependence of the Seebeck effect and its relationship to hopping transport theory. Furthermore, various theoretical methods are used to discuss carrier thermoelectric transport. Finally, an outlook of the remaining challenges ahead for future theoretical research is provided.

Magnetization currents of fluctuating Cooper pairs

Recent experiments show that the Nernst-Ettingshausen effect is orders of magnitude stronger than the thermoelectric Seebeck effect in superconductors above the critical temperature. We explain different magnitudes of the two effects accounting for the magnetization current of virtual Cooper pairs. The method allows for detailed understanding of the surprising non-monotonic dependence of the Nernst-Ettingshausen coefficient on the magnetic field.

(Invited) Advanced Nanostructured Thermoelectric Materials for Energy Conversion

The rapid development of nanomaterials in the past decade has provided a possibility of directly converting waste heat back to electricity based on the thermoelectric Seebeck effect. In the past four years, we have developed a transformative approach to pioneered low cost and scalable solution-phase growth methods to mass produce thermoelectric nanowires and nanowire heterostructures to match the physical and economic magnitudes of energy use and economical entertainment in the manufacture/recycling. These nanostructured thermoelectric materials show a significantly enhanced performance compared to the bulk crystals based on the quantum confinement and minority carrier blocking.

Thermoelectric Seebeck effect in oxide-based resistive switching memory.

Reversible resistive switching induced by an electric field in oxide-based resistive switching memory shows a promising application in future information storage and processing. It is believed that there are some local conductive filaments formed and ruptured in the resistive switching process. However, as a fundamental question, how electron transports in the formed conductive filament is still under debate due to the difficulty to directly characterize its physical and electrical properties. Here we investigate the intrinsic electronic transport mechanism in such conductive filament by measuring thermoelectric Seebeck effects. We show that the small-polaron hopping model can well describe the electronic transport process for all resistance states, although the corresponding temperature-dependent resistance behaviours are contrary. Moreover, at low resistance states, we observe a clear semiconductor–metal transition around 150 K. These results provide insight in understanding resistive switching process and establish a basic framework for modelling resistive switching behaviour.

Advanced Nanostructured Thermoelectric Materials for Energy Conversion

The rapid development of nanomaterials in the past decade has provided a possibility of directly converting waste heat back to electricity based on the thermoelectric Seebeck effect. In the past four years, we have developed a transformative approach to pioneered low cost and scalable solution-phase growth methods to mass produce thermoelectric nanowires and nanowire heterostructures to match the physical and economic magnitudes of energy use and economical entertainment in the manufacture/recycling. These nanostructured thermoelectric materials show a significantly enhanced performance compared to the bulk crystals based on the quantum confinement and energy filtering.

Electron effective mass in n-type electron-induced ferromagnetic semiconductor (In,Fe)As: Evidence of conduction band transport

The electron effective mass (m*) in n-type carrier-induced ferromagnetic semiconductor (In,Fe)As was estimated by using the thermoelectric Seebeck effect. It was found that m* is 0.03 ∼ 0.17m0 depending on the electron concentration, where m0 is the free electron mass. These values are similar to those of electrons in the conduction band of n+ InAs. The Fermi level EF in (In,Fe)As is located at least 0.15 eV above the conduction band bottom. Our results indicate that electron carriers in (In,Fe)As reside in the conduction band, rather than in a hypothetical Fe-related itinerant impurity band.

3D interface elements for modelling complex potential drops. Comparison with a boundary elements method

Voltage drops due to complex surface impedance and/or surface current sources are modelled by a 3D finite elements method. Two specific formulations are given with these special 3D curvilinear second order elements: conduction in a low frequency marine electrometer and thermoelectric Seebeck effect on a solidification front. Simultaneous normal and tangential interfacial discontinuities can be computed. The method is validated by comparison with a boundary elements method and experimental values. >