Fabrication of PEDOT:PSS/Ag2Se Nanowires for Polymer-Based Thermoelectric Applications

Recent trends and future perspectives of thermoelectric materials and their applications

This review explores the ever-evolving landscape of thermoelectric materials, focusing on the latest trends and innovations in ceramics, thermally conductive gel-like materials, metals, nanoparticles, polymers, and silicon. Thermoelectric materials have garnered significant attention for their capability to convert waste heat into electrical power, positioning them as promising candidates for energy harvesting and cooling applications. This review distinguishes itself by highlighting recent advancements in synthesis methods, advanced doping strategies, and nanostructuring techniques that have markedly enhanced material performance. It provides a comprehensive analysis of the controlled properties concerning their synthesis parameters, such as electrical conductivity, Seebeck coefficient, and thermal conductivity. Furthermore, this work delves into the emerging applications of thermoelectric devices across diverse fields, including automotive, aerospace, wearable electronics, and industrial waste heat recovery. By offering forward-looking insights, this review outlines thermoelectric devices' challenges and future prospects, underscoring their potential to contribute to sustainable energy solutions and efficient thermal management systems. By integrating current trends with future projections, this review offers a timely and comprehensive roadmap for researchers and engineers dedicated to advancing next-generation thermoelectric technologies.

Thermoelectric Silver-Based Chalcogenides

Heat is abundantly available from various sources including solar irradiation, geothermal energy, industrial processes, automobile exhausts, and from the human body and other living beings. However, these heat sources are often overlooked despite their abundance, and their potential applications remain underdeveloped. In recent years, important progress has been made in the development of high-performance thermoelectric materials, which have been extensively studied at medium and high temperatures, but less so at near room temperature. Silver-based chalcogenides have gained much attention as near room temperature thermoelectric materials, and they are anticipated to catalyze tremendous growth in energy harvesting for advancing internet of things appliances, self-powered wearable medical systems, and self-powered wearable intelligent devices. This review encompasses the recent advancements of thermoelectric silver-based chalcogenides including binary and multinary compounds, as well as their hybrids and composites. Emphasis is placed on strategic approaches which improve the value of the figure of merit for better thermoelectric performance at near room temperature via engineering material size, shape, composition, bandgap, etc. This review also describes the potential of thermoelectric materials for applications including self-powering wearable devices created by different approaches. Lastly, the underlying challenges and perspectives on the future development of thermoelectric materials are discussed.

From Brittle to Ductile: A Scalable and Tailorable All-Inorganic Semiconductor Foil through a Rolling Process toward Flexible Thermoelectric Modules

Inorganic thermoelectric (TE) materials with outstanding capacity for energy conversion are expected to be promising eco-friendly and renewable power sources, but they are always intrinsically brittle, restricting their development in flexible TE electronics. Therefore, we have developed a facile manufacturing method of large-scale all-inorganic silver chalcogenide foils and flexible TE generators in this work. A rolling process, as an effective and facile molding technique, is applied in ductile TE materials. The figure-of-merit for flexibility of this free-standing foil is in the range of 0.02-0.13, suggesting the superior flexibility of the all-inorganic TE foils. A high TE figure-of-merit ZT of 0.47 at room temperature is reached for Ag₂S_0.45Se_0.45Te_0.1, which is one of the most promising room-temperature ZTs among flexible TE materials. A proof-of-concept flexible TE generator based on silver chalcogenide foils achieves an open-circuit voltage of 1.19 mV and an output power density of 1.8 mW/m² with a temperature difference of 2.7 °C across the TE leg, showing great potential in heat-to-electricity conversion.

Facile Fabrication of N-Type Flexible CoSb3-xTex Skutterudite/PEDOT:PSS Hybrid Thermoelectric Films

Alongiside the growing demand for wearable and implantable electronics, the development of flexible thermoelectric (FTE) materials holds great promise and has recently become a highly necessitated and efficient method for converting heat to electricity. Conductive polymers were widely used in previous research; however, n-type polymers suffer from instability compared to the p-type polymers, which results in a deficiency in the n-type TE leg for FTE devices. The development of the n-type FTE is still at a relatively early stage with limited applicable materials, insufficient conversion efficiency, and issues such as an undesirably high cost or toxic element consumption. In this work, as a prototype, a flexible n-type rare-earth free skutterudite (CoSb₃)/poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS) binary thermoelectric film was fabricated based on ball-milled skutterudite via a facile top-down method, which is promising to be widely applicable to the hybridization of conventional bulk TE materials. The polymers bridge the separated thermoelectric particles and provide a conducting pathway for carriers, leading to an enhancement in electrical conductivity and a competitive Seebeck coefficient. The current work proposes a rational design towards FTE devices and provides a perspective for the exploration of conventional thermoelectric materials for wearable electronics.

Improved thermoelectric properties of multi-walled carbon nanotubes/Ag2Se via controlling the composite ratio

MWCNTs/Ag2Se composites were synthesized via a facile hydrothermal method; higher electrical conductivity and lower thermal conductivity were simultaneously achieved compared with Ag2Se, resulting in enhanced thermoelectric performance.

Conductive PEDOT: PSS-Based Organic/Inorganic Flexible Thermoelectric Films and Power Generators

We present a simple thermoelectric device that consists of a conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-based inorganic/organic thermoelectric film with high thermoelectric performance. The PEDOT:PSS-coated Se NWs were first chemically synthesized in situ, and then mixed with an Ag precursor solution to produce the PEDOT:PSS-coated Ag₂Se NWs. The PEDOT:PSS matrix was then treated with dimethyl sulfoxide (DMSO) prior to the production of flexible PEDOT:PSS-coated Ag₂Se NW/PEDOT:PSS composite films with various weight fractions of Ag₂Se via a simple drop-casting method. The thermoelectric properties (Seebeck coefficient, electrical conductivity, and power factor) of the composite films were then analyzed. The composite film with 50 wt.% NWs exhibited the highest power factor of 327.15 μW/m·K² at room temperature. The excellent flexibility of this composite film was verified by bending tests, in which the thermoelectric properties were reduced by only ~5.9% after 1000 bending cycles. Finally, a simple thermoelectric device consisting of five strips of the proposed composite film was constructed and was shown to generate a voltage of 7.6 mV when the temperature difference was 20 K. Thus, the present study demonstrates that that the combination of a chalcogenide and a conductive composite film can produce a high-performance flexible thermoelectric composite film.