Nanoscale self-assembly of thermoelectric materials: a review of chemistry-based approaches

Abstract

This review is concerned with the leading methods of bottom-up material preparation for thermal-to-electrical energy interconversion. The advantages, capabilities, and challenges from a material synthesis perspective are surveyed and the methods are discussed with respect to their potential for improvement (or possibly deterioration) of application-relevant transport properties. Solution chemistry-based synthesis approaches are re-assessed from the perspective of thermoelectric applications based on reported procedures for nanowire, quantum dot, mesoporous, hydro/solvothermal, and microwave-assisted syntheses as these techniques can effectively be exploited for industrial mass production. In terms of energy conversion efficiency, the benefit of self-assembly can occur from three paths: suppressing thermal conductivity, increasing thermopower, and boosting electrical conductivity. An ideal thermoelectric material gains from all three improvements simultaneously. Most bottom-up materials have been shown to exhibit very low values of thermal conductivity compared to their top-down (solid-state) counterparts, although the main challenge lies in improving their poor electrical properties. Recent developments in the field discussed in this review reveal that the traditional view of bottom-up thermoelectrics as inferior materials suffering from poor performance is not appropriate. Thermopower enhancement due to size and energy filtering effects, electrical conductivity enhancement, and thermal conductivity reduction mechanisms inherent in bottom-up nanoscale self-assembly syntheses are indicative of the impact that these techniques will play in future thermoelectric applications.

Optical and Thermoelectric Properties of Surface-Oxidation Sensitive Layered Zirconium Dichalcogenides ZrS2−xSex (x = 0, 1, 2) Crystals Grown by Chemical Vapor Transport

“…In earlier research, the first principle thermoelectric properties of zirconium dichalcogenides was reported by a number of authors [20,21]; nevertheless, experimental works on thermoelectric properties of ZrX 2 (X = S, Se) have rarely been reported. Some of the 1D nanowire and nanoscale thermoelectric materials have been claimed to have improved thermo-electronic transport property [22,23]; however, to date, experimental thermoelectric measurements on the Zr-based ZrS 2 , ZrSSe, and ZrSe 2 layered TMDCs are seldom found in the literature, in spite of some thermoelectric materials [24][25][26][27] having been reported for power-generation applications. In this paper, the optical and thermoelectric properties of ZrS 2−x Se x (x = 0, 1, and 2) were characterized using temperature-dependent transmittance, Raman, and thermoelectric measurements from low to room temperature.…”

High efficiency Mg2(Si,Sn)-based thermoelectric materials: scale-up synthesis, functional homogeneity, and thermal stability

“…To enhance this scattering effect, alloying with both heavier and larger isoelectronic atoms, such as germanium (Ge) [26][27][28] and tin (Sn) 29-32 on the Si position, have demonstrated to efficaciously reduce the thermal conductivity by 70% as compared to its non-alloyed value (from $10 W m À1 K À1 to $2.5 W m À1 K À1 ). 10,17 In order to reach lattice thermal conductivity values close to the alloy limit, phonons with a wide range of wavelengths need to be scattered via integrating other strategies, such as nanostructuring, [33][34][35][36] nano-inclusion, 10,37-39 and modulation doping, 40 with alloying. The best performing materials in the Mg 2 (Si,Sn) system usually contain $23 AE 3 at% Sn, which is where the conduction band convergence is taking place, 41,42 and all exhibit a maximum gure of merit, zT max , of 1.4 AE 0.2, satisfactory for the device applications.…”

Growth of quantum dot coated core-shell anisotropic nanowires for improved thermal and electronic transport

“…1,2 For instance, thermal transport can create an uneven distribution of charge carriers in semiconductors (e.g., thermoelectric effect), which could provide a global sustainable energy solution by generating electricity from waste heat. 1,3,4 The fundamental principle underlying the thermal transport is the flow of electrons and phonons that carry heat and charge under a thermal gradient. 3 In semiconductors, this dynamic process has been theoretically rationalized as ZT ¼ rS 2 T/(j el þ j lat ) (i.e., Peltier-Seebeck Effect), where ZT is the dimensionless figure of merit, r is the electrical conductivity, T is the temperature, S is the Seebeck coefficient, and j lat and j el are the lattice and electronic thermal conductivities (j ¼ j el þ j lat ).…”