Effect of transport in a semiconductor thermoelectric generator on its efficiency

The effects of electrical transport and thermal diffusion in the working medium of a thermoelectric generator (TEG) on its efficiency and maximum useful power are examined. Equations are derived to describe these effects, and dimensionless parameters are found whose values are governed by the thermodynamic and kinetic characteristics of the material. Numerical estimates carried out show that it is possible to increase the efficiency and power of a TEG by selecting materials having suitable transport characteristics. The semiconductor alloys of the T1-S system are interesting in this regard.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 8, pp. 63–69, August, 1969.     

Study of the performance of a thermoelectric generator transformation of the thermal energy conveyed by a heat transfer fluid into electrical energy

A mathematical model to predict the maximum energy conversion efficiency of the thermoelectric generator is developed to improve the performance and maximize the energy conversion efficiency of the thermoelectric power generator. The studied device corresponds to an original configuration of thermoelectric modules mounted on the peripheral surfaces of two channels, one of the channels is crossed by hot fluid and the other by a cold fluid. First, the effect of the flow rate was studied to choose the flow rate adapted to our study for three different configurations of the thermopile, the co-current configuration, the counter-current configuration, and the sandwich configuration. Then a comparison was made to choose the best configuration between these three studied configurations by addressing their thermoelectric performances. The results revealed that the sandwich configuration is much better than the co-current and counter-current configurations and reduces the surface area occupied by the TEG by half while generating more power than a solar panel.     

Generating power of a thermoelectric generator under periodically alternating temperature gradients

The thermo-emf ΔV and thermoelectric current ΔI generated by imposing a temperature gradient alternating at a period of T on a thermoelectric (TE) generator were measured as a function of t, where t is the lapsed time and 1/T was varied from 0 to 1/30 s^-1. A TE generator was sandwiched between two Peltier modules connected in series. The alternating temperature gradients were produced by imposing an alternating voltage V on two Peltier modules, where V was varied from 1.0 to 3.7 V. Both ΔV and ΔI generated by the TE generator oscillate at a period of T but their amplitudes tend to increase monotonically with an increase of V. The effective thermo-emf ΔV_eff and current ΔI_eff calculated from ΔV and ΔI increase abruptly with an increase of 1/T and have a local maximum at 1/T=1/120 or 1/240 s^-1. The generating power ΔW_eff(=ΔV_effΔI_eff) tends to increase proportionally with an increase of input power W_input, owing to the increase in the temperature difference. The rate of ΔW_eff to W_input at 1/T=1/240 s^-1 reached approximately 3.2 times as large as that obtained for the steady temperature gradient corresponding to 1/T=0 s^-1. It was thus found that the generating power of the TE generator operating under the temperature gradient alternating at an optimum period is remarkably increased compared to that of a TE generator working under a conventional steady temperature gradient. PACS 72.15.Jf; 84.60.Rb; 85.30De     

Flexible thermoelectric module based on zinc oxide thin film grown via SILAR

In this work, we used the low temperature solution growth Successive Ionic Layer Adsorption and Reaction (SILAR) for a deposition of the nanostructured undoped and indium doped (ZnO and ZnO:In) thin films on flexible polyimide (PI) substrates for their use as cheap non-toxic thermoelectric materials in the flexible thermoelectric modules of planar type to power up portable and wearable electronics and miniature devices. The use of a zincate solution in the SILAR method allows to obtain ZnO:In film, which after post-growth annealing at 300 °C has low resistivity ρ ≈ 0.02 Ω m, and high Seebeck coefficient −147 μV/K and thermoelectric power factor ~1 μW K⁻² m⁻¹ at near-room temperatures. As evidence of the operability of the manufactured films as the basis of the TE device, we have designed and tested experimental lightweight thin-film thermoelectric module. This TE module is able to produce specific output power 0.8 μW/m² at ΔT = 50 K.     

N-type core-shell heterostructured Bi2S3@Bi nanorods/polyaniline hybrids for stretchable thermoelectric generator

With the growing need on distributed power supply for portable electronics,energy harvesting from environment becomes a promising solution.Organic thermoelectric(TE)materials have advantages in intrinsic flexibility and low thermal conductivity,thus hold great prospect in applications as a flexible power generator from dissipated heat.Nevertheless,the weak electrical transport behaviors of organic TE materials have severely impeded their development.Moreover,compared with p-type organic TE materials,stable and high-performance n-type counterparts are more difficult to obtain.Here,we developed a n-type polyaniline-based hybrid with core-shell heterostructured Bi;S;@Bi nanorods as fillers,showing a Seebeck coefficient-159.4μV/K at room temperature.Further,a couple of n/p legs from the PANI-based hybrids were integrated into an elastomer substrate forming a stretchable thermoelectric generator(TEG),whose function to output stable voltages responding to temperature differences has been demonstrated.The in situ output performance of the TEG under stretching could withstand up to 75%elongation,and stability test showed little degradation over a one-month period in the air.This study provides a promising strategy to develop stable and high thermopower organic TEGs harvesting heat from environment as long-term power supply.     

Performance of thermoelectric generator with graphene nanofluid cooling

Improvement of the heat transfer of the cold side is one of the approaches to enhance the performance of TEG systems.As a new type of heat transfer media, nanofluids can enhance the heat transfer performance of working liquid significantly.Based on a three-dimensional and steady-state numerical model,the heat transfer and thermoelectric conversion properties of TEG systems were studied. Graphene anoplatelet aqueous nanofluids were used as the coolants for the cold side of the TEG system to improve the heat transfer capacity of the cold side. The results showed that the heat absorbed by the hot side, voltage, output power, and conversion efficiency of the TEG system were increased greatly by the nanofluid coolants.The output power and the conversion efficiency using 0.1-wt% graphene nanoplatelet aqueous nanofluid as the coolant are enhanced by 26.39% and 14.74%, respectively.     

平板集热太阳热电器件建模及结构优化

太阳能热电转换是光伏效应外另一种直接将太阳辐射转变为电能的途径, 近年来已经成为太阳能利用的热点之一. 本文以Bi₂Te₃材料为基础构建平板集热太阳热电器件模型, 采用有限元法分析AM1.5辐射条件下器件温度分布情况, 并结合基于温度的物性参数计算集热比、热臂截面积与长度变化等因素对器件的开路电压、 最大输出功率及转化效率的影响. 研究发现: 集热比与热臂长度的变化对器件性能有显著影响, 热臂截面积的变化对器件转化效率影响相对较弱; 在这一模型中, 平板集热太阳热电器件的转化效率达到1.56%.     

高光谱吸收微纳结构表面提高太阳能温差发电性能的研究

采用飞秒激光等离子体丝（飞秒光丝）在金属铝箔表面以不同飞秒光丝扫描速度（5,15,25,35和45 mm·s-1）制备了微纳结构表面,并在太阳光能量主要覆盖的光谱范围（330～890 nm）内对其进行了反射率测量,发现飞秒光丝制备的微纳结构表面具有显著的高光谱吸收特性,并且飞秒光丝扫描速度越慢,光谱吸收率越强,5 mm·s-1条件下微纳结构表面光谱吸收率达97%以上。将制备的高光谱吸收微纳结构表面作为温差发电片（TEG）光吸收体,以此为基础构建了考虑太阳光辐照及温差发电模块（即TEG模块：结合微纳结构表面的TEG）散热情况的仿真实验环境并进行发电功率测量。研究结果表明,具有微纳结构的铝表面（5 mm·s-1制备条件下）与抛光铝箔或裸发电片相比,光电转化效率（发电效率）可分别提高43.3和10.7倍。进一步研究了TEG模块的温差发电的过程与机理,将TEG模块的温差发电过程分为光热（光能转化为热能）与热电（热能转化为电能）两个转化过程分析：首先在光热转化过程中,微纳结构表面增强了太阳光吸收效率,为光热转化提供更多的光子能量,实现了其在表面更多的热量沉积,进而在之后的热电转化过程中,更多的热能沉积使得TEG模块的载流子迁移率得到了很大提升,这样在同样的温差（发电片冷热端的温度差值）条件下,微纳结构表面与普通表面相比可以获得更高的热电转化效率。因此,微纳结构表面的高光谱吸收性能使得TEG模块经光热转化后得到的高热能沉积使载流子迁移率得到了提高,进而显著提升了TEG模块发电性能,这是微纳结构表面增强TEG温差发电效率的主要原因。这一机理的揭示,为TEG模块发电性能的进一步优化和提升提供了理论依据,对TEG模块的实际应用具有重要的意义。     

Study on the thermoelectric properties of porous Bi-Te films deposited using thermal evaporation on AAO template

The application of thermoelectric films is limited to retain the temperature gradient. In this study, the Bi-Te films are deposited on the AAO template with a pore size of 100 nm using thermal evaporation. The results show that the conductive types of the Bi-Te film are tuned by source temperature. The power factor of the p-type porous film decreases 36% by comparing to that of the p-type nonporous film (1020 μW/mK² at 250 °C). Meanwhile, the temperature difference in the porous device is maintained and is approximately 5.0 °C. Thus, the maximum output power is achieved in the porous device (about 25 pW), which is 5 times higher than that of the nonporous device. This provides a method to improve the conversion efficiency of thermoelectric film device by maintaining the temperature difference by using porous structure.     

Impurities-contributed abnormal thermoelectric effect in a parallel double quantum dot structure

We discuss the influence of local impurities on the thermoelectric effect in a parallel double quantum dot (QD) structure. It is first found that in this structure, the Fano effect contributes significantly to the enhancement of thermoelectric efficiency, especially in the case of ϕ = π. Next, impurities are introduced to couple to the QDs, respectively. We readily find that regardless of which QD is coupled to a local impurity, the thermoelectric efficiency can be enhanced by the strengthening of impurity–QD coupling. This means that the destruction of the Fano interference is not the necessary condition to suppress the thermoelectric effect. Accordingly, we hope that the numerical results can help to understand the role of impurities in adjusting the thermoelectric properties of the QD structure.     

Structural,morphological and thermoelectric properties of self-decorated copper selenide nanosheets synthesized at room temperature

In this work, an economical, surfactant-free and scalable solution synthesis method at room temperature for self-decorated copper selenide (Cu_2-xSe) nanosheets is reported. Structural and morphological characterizations clearly revealed the formation of single cubic phase Cu_2-xSe nanosheets in nearly stoichiometric ratio. The tentative mechanism for fabrication of self-decorated Cu_2-xSe nanosheets was proposed. Furthermore, nanostructured bulk Cu_2-xSe by hot pressing was explored for thermoelectric performance. High electrical conductivity (1.1 × 10⁵ S/m), moderate Seebeck coefficient (87 μV/K) and low thermal conductivity (1.11 W/mK) at 753 K were obtained. The figure of merit (ZT) ~ 0.56 and power factor (PF) ~ 860 μW/mK² at 753 K showed better performance than some reported Cu_2-xSe nanostructured or bulk counterparts under same temperature. Also, theoretically device ZT ~0.16 and efficiency up to 3% could be achieved. The results indicate that this green and novel synthesis process is an alternative to other reported time or energy consuming processes.     

Selecting the optimum method of heat transfer intensification to improve efficiency of thermoelectric generator

The relevance of applying the methods of energy recovery from exhaust gases is substantiated. The principle of operation of a thermoelectric generator is described, the variant of its design is proposed, and the efficiency of various design methods of heat exchange intensification is compared. Designs are compared with a baseline configuration without heat transfer intensifiers in terms of coefficients of gas dynamic resistance ξ/ξ₀ and the ratio of dimensionless criteria Nu/Nu₀. The results of comparative analysis have proved the applicability of the methods of heat exchange intensification in the design of thermoelectric generators of various vehicles.     

Module-level design and characterization of thermoelectric power generator

Thermoelectric power generation provides us the unique capability to explore the deep space and holds promise for harvesting the waste heat and providing a battery-free power supply for IoTs. The past years have witnessed massive progress in thermoelectric materials, while the module-level development is still lagged behind. We would like to shine some light on the module-level design and characterization of thermoelectric power generators (TEGs). In the module-level design, we review material selection, thermal management, and the determination of structural parameters. We also look into the module-level characterization, with particular attention on the heat flux measurement. Finally, the challenge in the optimal design and reliable characterization of thermoelectric power generators is discussed, together with a calling to establish a standard test procedure.     

Thermoelectric generator based on a bismuth-telluride alloy fabricated by addition of ethylene glycol

This paper introduces a new method to selectively fabricate n-type and p-type bismuth (Bi)-telluride (Te) thermoelectric materials by the rate of addition of ethylene glycol (EG) in the Bi–Te co-electrodeposition solution. As the amount of added EG is increased, the atomic ratio of Bi in the deposited Bi–Te alloy reached a slope of 0.463 (at.% of Bi/vol.% of EG), and increased in a linear manner. When the EG content reached approximately 20%v/v, the n-type material changed into a p-type. This change implies that adjusting the EG content in the electrodeposition solution affords simple control of the Bi–Te composition. To demonstrate the applicability of the developed thermoelectric materials, thermoelectric generators (TEGs) were fabricated using electrodeposited n-type (using solution without EG) and p-type (using solution with 30%v/v EG) Bi–Te alloys. The Seebeck voltage of the pair of n-type and p-type thermoelectric materials was 140 mV and the power generated from the pair was 24.36 nW at a 10 °C temperature difference.     

Enhanced thermoelectric power in dual-gated bilayer graphene

The thermoelectric power of a material, typically governed by its band structure and carrier density, can be varied by chemical doping that is often restricted by solubility of the dopant. Materials showing large thermoelectric power are useful for many industrial applications, such as the heat-to-electricity conversion and the thermoelectric cooling device. Here we show a full electric-field tuning of thermoelectric power in a dual-gated bilayer graphene device resulting from the opening of a band gap by applying a perpendicular electric field on bilayer graphene. We uncover a large enhancement in thermoelectric power at a low temperature, which may open up a new possibility in low temperature thermoelectric application using graphene-based device.     

Measuring thermoelectric property of nano-heterostructure

A method of measuring the thermoelectric power of nano-heterostructures based on four-probe scanning tunneling microscopy is presented. The process is composed of the it in-situ fabrication of a tungsten-indium tip, the precise control of the tip-sample contact and the identification of thermoelectric potential. When the temperature of the substrate is elevated, while that of the tip is kept at room temperature, a thermoelectric potential occurs and can be detected by a current-voltage measurement. As an example of its application, the method is demonstrated to be effective to measure the thermoelectric power in several systems. A Seebeck coefficient of tens of μV/K is obtained in graphene epitaxially grown on Ru (0001) substrate and the thermoelectric potential polarity of this system is found to be the reverse of that of bare Ru (0001) substrate.     

太阳能光伏-温差发电驱动的新型冰箱模型设计与热力学分析

结合太阳能电池温度特性和温差发电特点,设计了一套新的太阳能光伏发电-温差发电驱动的冰箱模型,该模型包括太阳能光伏电池、半导体温差发电模块、电源控制系统等.根据负载用电需求,做出了光伏发电系统的设计方案.采用热力学基本理论,对该模型进行了工作效率及 火 用 效率的分析.结果发现:能效比COP达到了2.73(一般 冰箱COP为2左右), 火 用 效率也达到42.5%.同时,该系统模型环境效益明显,可以减排CO₂ 1394.2 kg,SO₂     

Thermoelectric efficiency and compatibility

The intensive reduced efficiency eta(r) is derived for thermoelectric power generation (in one dimension) from intensive fields and currents, giving eta(r)=(E x J) divided by (- inverted Delta)T x J(S). The overall efficiency is derivable from a thermodynamic state function, Phi=1 divided by u + alphaT, where we introduce u=J divided by kappa (inverted Delta)T as the relative current density. The method simplifies the computation and clarifies the physics behind thermoelectric devices by revealing a new materials property s=(sqrt[1+zT]-1) divided by (alphaT), which we call the compatibility factor. Materials with dissimilar compatibility factors cannot be combined by segmentation into an efficient thermoelectric generator because of constraints imposed on u. Thus, control of the compatibility factor s is, in addition to z, essential for efficient operation of a thermoelectric device, and thus will facilitate rational materials selection, device design, and the engineering of functionally graded materials.     

Improving the thermoelectric properties of carbon nanotubes through introducing graphene nanosprings

Carbon nanotube (CNT) is a typical one-dimensional nanomaterial containing sp² hybridization states. In this paper, we investigate the ballistic thermoelectric performance of CNTs incorporating graphene nanosprings by using non-equilibrium Green's function. The calculations reveal that the thermoelectric figure of merit could be obviously improved by introducing graphene nanosprings, which is about ten times of that of pristine CNTs at 700 K. Such enhancement is mainly attributed to the remarkable suppression of phononic and electronic thermal conductance and improvement of Seebeck coefficient. In addition, compared to the zigzag graphene nanospring, introducing of the armchair case possesses better thermoelectric performance. The results presented in this paper indicate that embedding graphene nanospring is a viable method to optimize the thermoelectric performance of CNTs and could provide useful theoretical guidance for design and fabrication of CNTs-based thermoelectric devices.