Screen-Printed Flexible Thermoelectric Device Based on Hybrid Silver Selenide/PVP Composite Films

The Latest Advances in Ink-Based Nanogenerators: From Materials to Applications

Nanogenerators possess the capability to harvest faint energy from the environment. Among them, thermoelectric (TE), triboelectric, piezoelectric (PE), and moisture-enabled nanogenerators represent promising approaches to micro-nano energy collection. These nanogenerators have seen considerable progress in material optimization and structural design. Printing technology has facilitated the large-scale manufacturing of nanogenerators. Although inks can be compatible with most traditional functional materials, this inevitably leads to a decrease in the electrical performance of the materials, necessitating control over the rheological properties of the inks. Furthermore, printing technology offers increased structural design flexibility. This review provides a comprehensive framework for ink-based nanogenerators, encompassing ink material optimization and device structural design, including improvements in ink performance, control of rheological properties, and efficient energy harvesting structures. Additionally, it highlights ink-based nanogenerators that incorporate textile technology and hybrid energy technologies, reviewing their latest advancements in energy collection and self-powered sensing. The discussion also addresses the main challenges faced and future directions for development.

Largely Enhanced Thermoelectric Performance of Flexible Ag2Se Film by Cationic Doping and Dual-Phase Engineering

Recent studies have shown that silver selenide is a promising thermoelectric material at room temperature. Herein, flexible films with a nominal composition of (Ag1-xCux)2Se are prepared by a simple and efficient one-pot method combined with vacuum-assisted filtration and hot pressing. The thermoelectric properties of the films are regulated by both cationic doping and a dual-phase strategy via a wet chemical method. As the x increases, not only Cu is doped into the Ag2Se, but different new phases (CuAgSe and/or CuSe2) also appear. The (Ag1-xCux)2Se film with x = 0.02 composed of Cu-doped Ag2Se and CuAgSe shows a high PF of ∼2540 μW m-1 K-2 (ZT ∼ 0.90) and outstanding flexibility at room temperature. The high thermoelectric properties of the film are due to the effect of Cu doping and the CuAgSe phase, including the increase in electrical conductivity caused by doping, the enhanced phonon scattering at the Ag2Se/CuAgSe interface, and the interaction between the energy filtering effect and the doping effect. In addition to the high output performance (PDmax = 28.08 W m-2, ΔT = 32.2 K), the flexible device assembled with the (Ag0.98Cu0.02)2Se film also has potential applications as a temperature sensor.

Evolution of Thermoelectric Generators: From Application to Hybridization

Considerable thermal energy is emitted into the environment from human activities and equipment operation in the course of daily production. Accordingly, the use of thermoelectric generators (TEGs) can attract wide interest, and it shows high potential in reducing energy waste and increasing energy recovery rates. Notably, TEGs have aroused rising attention and been significantly boosted over the past few years, as the energy crisis has worsened. The reason for their progress is that thermoelectric generators can be easily attached to the surface of a heat source, converting heat energy directly into electricity in a stable and continuous manner. In this review, applications in wearable devices, and everyday life are reviewed according to the type of structure of TEGs. Meanwhile, the latest progress of TEGs' hybridization with triboelectric nanogenerator (TENG), piezoelectric nanogenerator (PENG), and photovoltaic effect is introduced. Moreover, prospects and suggestions for subsequent research work are proposed. This review suggests that hybridization of energy harvesting, and flexible high-temperature thermoelectric generators are the future trends.

Recent research trends in textile-based temperature sensors: a mini review

In this review, the current state of research on textile-based temperature sensors is explored by focusing on their potential use in various applications. The textile-based sensors show various advantages including flexibility, conformability and seamlessness for the wearer. Integration of the textile-based sensors into clothes or fabric-based products enables continuous and sensitive monitoring of change in temperature, which can be used for various medical and fitness applications. However, there are lacks of comprehensive review on the textile-based temperature sensors. This review introduces various types of textile-based temperature sensors, including resistive, thermoelectric and fibre-optical sensors. In addition, the challenges that need to be addressed to fully realise their potential, which include improving sensitivity and accuracy, integrating wireless communication capabilities, and developing low-cost fabrication techniques. The technological advances in textile-based temperature sensors to overcome the limitations will revolutionize wearable devices requiring function of temperature monitoring.

Ag2 Q-Based (Q = S, Se, Te) Silver Chalcogenide Thermoelectric Materials

Thermoelectric technology provides a promising solution to sustainable energy utilization and scalable power supply. Recently, Ag₂ Q-based (Q = S, Se, Te) silver chalcogenides have come forth as potential thermoelectric materials that are endowed with complex crystal structures, high carrier mobility coupled with low lattice thermal conductivity, and even exceptional plasticity. This review presents the latest advances in this material family, from binary compounds to ternary and quaternary alloys, covering the understanding of multi-scale structures and peculiar properties, the optimization of thermoelectric performance, and the rational design of new materials. The "composition-phase structure-thermoelectric/mechanical properties" correlation is emphasized. Flexible and hetero-shaped thermoelectric prototypes based on Ag₂ Q materials are also demonstrated. Several key problems and challenges are put forward concerning further understanding and optimization of Ag₂ Q-based thermoelectric chalcogenides.

Flexible Thermoelectric Reduced Graphene Oxide/Ag2S/Methyl Cellulose Composite Film Prepared by Screen Printing Process

As an organic-inorganic thermoelectric composite material, a flexible, reduced graphene oxide (rGO)/silver sulfide (Ag₂S)/methyl cellulose (MC) film was fabricated by a two-step method. Firstly, a rGO/Ag₂S composite powder was prepared by a chemical synthesis method, and then, the rGO/Ag₂S/MC composite film was prepared by a combined screen printing and annealing treatment process. The rGO and rGO/Ag₂S composite powders were evenly dispersed in the rGO/Ag₂S/MC composite films. A power factor of 115 μW m^-1 K^-2 at 520 K was acquired for the rGO/Ag₂S/MC composite film, which is ~958 times higher than the power factor at 360 K (0.12 μW m^-1 K^-2), mainly due to the significant increase in the electrical conductivity of the composite film from 0.006 S/cm to 210.18 S/cm as the test temperature raised from 360 K to 520 K. The as-prepared rGO/Ag₂S/MC composite film has a good flexibility, which shows a huge potential for the application of flexible, wearable electronics.

High Seebeck Coefficient from Screen-Printed Colloidal PbSe Nanocrystals Thin Film

Thin-film thermoelectrics (TEs) with a thickness of a few microns present an attractive opportunity to power the internet of things (IoT). Here, we propose screen printing as an industry-relevant technology to fabricate TE thin films from colloidal PbSe quantum dots (QDs). Monodisperse 13 nm-sized PbSe QDs with spherical morphology were synthesized through a straightforward heating-up method. The cubic-phase PbSe QDs with homogeneous chemical composition allowed the formulation of a novel ink to fabricate 2 μm-thick thin films through robust screen printing followed by rapid annealing. A maximum Seebeck coefficient of 561 μV K^-1 was obtained at 143 °C and the highest electrical conductivity of 123 S m^-1 was reached at 197 °C. Power factor calculations resulted in a maximum value of 2.47 × 10^-5 W m^-1 K^-2 at 143 °C. To the best of our knowledge, the observed Seebeck coefficient value is the highest reported for TE thin films fabricated by screen printing. Thus, this study highlights that increased Seebeck coefficients can be obtained by using QD building blocks owing to quantum confinement.

Preparation and Characterization of Screen-Printed Cu2S/PEDOT:PSS Hybrid Films for Flexible Thermoelectric Power Generator

In recent years, flexible thermoelectric generators(f-TEG), which can generate electricity by environmental temperature difference and have low cost, have been widely concerned in self-powered energy devices for underground pipe network monitoring. This paper studied the Cu₂S films by screen-printing. The effects of different proportions of p-type Cu₂S/poly 3,4-ethylene dioxythiophene-polystyrene sulfonate (PEDOT:PSS) mixture on the thermoelectric properties of films were studied. The interfacial effect of the two materials, forming a superconducting layer on the surface of Cu₂S, leads to the enhancement of film conductivity with the increase of PEDOT:PSS. In addition, the Seebeck coefficient decreases with the increase of PEDOT:PSS due to the excessive bandgap difference between the two materials. When the content ratio of Cu₂S and PEDOT:PSS was 1:1.2, the prepared film had the optimal thermoelectric performance, with a maximum power factor (PF) of 20.60 μW·m^-1·K^-1. The conductivity reached 75% of the initial value after 1500 bending tests. In addition, a fully printed Te-free f-TEG with a fan-shaped structure by Cu₂S and Ag₂Se was constructed. When the temperature difference (ΔT) was 35 K, the output voltage of the f-TEG was 33.50 mV, and the maximum power was 163.20 nW. Thus, it is envisaged that large thermoelectric output can be obtained by building a multi-layer stacking f-TEG for continuous self-powered monitoring.