Realizing High Thermoelectric Performance of Bi-Sb-Te-Based Printed Films through Grain Interface Modification by an In Situ-Grown β-Cu2-δSe Phase

Ordered Architectonics of Magnetic Units Triggering Excellent Electrothermal Conversion Performance of Thick Films

The low electrical transport performance of flexible thermoelectric (TE) films is the bottleneck that restricts the development of in-plane heat dissipation technology based on the Peltier effect. The architectonics of magnetic units in TE materials have been proven to be an effective method to improve the efficiency of TE conversion. In this study, a series of Bi0.5Sb1.5Te3 (BST)/Fe/BST thermoelectromagnetic (TEM) films were successfully prepared by ordered architectonics of ferromagnetic Fe nanoparticles (Fe-NPs) as magnetic units with different distribution shapes between two layers of BST/epoxy films through screen-printing combined with hot-pressing curing. The study focused on the effects of the architectonic shapes of Fe magnetic units on the microstructure and electrothermal transport properties of TEM films. The ordered architectonics of magnetic units could optimize the carrier transport pathways and reduce carrier scattering due to the altered carrier trajectories induced by the magnetic field generated by the Fe magnetic unit, which has been confirmed by the magnetoresistance test, thus effectively enhancing σ. The introduction of the Fe magnetic unit preserved a large α through magnetic scattering and spin entropy contributions. The TEM film with Fe magnetic units patterned as rhombic shapes (BST-RhoFe-BST film) realized a 36.5% enhancement in the maximum power factor (PF), attributing to the largest negative magnetoresistance. The cooling temperature difference of the single-leg film device fabricated by the BST-RhoFe-BST film reached 1.8 K, 125% higher than that of the device fabricated by the BST-BST film. Furthermore, the cascade device based on the TEM film realized a temperature drop of 2.8 K and exhibited excellent in-plane heat dissipation capability. This work reveals that the ordered architectonic shapes of magnetic units could effectively regulate the electrothermal conversion performance of TE films, and the magnetoresistance theory can reveal the scattering mechanism of charge carriers in TEM films.

Cu- or Ag-containing Bi-Sb-Te for in-line roll-to-roll patterned thin-film thermoelectrics

The Selective Metallization Technique shows promise for roll-to-roll in-line patterning of flexible electronics using evaporated metals, but challenges arise when applied to sputtering functional materials. This study overcomes these challenges with simultaneous sputtering of Bi-Sb-Te and evaporation of metal (Ag or Cu) for thermoelectric layers when using Selective Metallization Technique. Large-scale manufacturing is demonstrated through roll-to-roll processing of a 0.8 m wide polymer web at 25 m/min, achieving high-throughput production of functional thin-film patterns with nanometer thickness. The room-temperature-deposited material system exhibits significantly enhanced thermoelectric performance and facilitates an n-type-to-p-type transition in the Cu- or Ag-containing Bi-Sb-Te-based composite film. Here, we show that while applying Selective Metallization Technique, the evaporation of metal modifies the impact of residual oil on Bi-Sb-Te, which can be effectively removed with a few seconds of plasma exposure, and the fabricated thermoelectric devices are validated in wearable applications utilizing a coiled-up wristband design.

Facile Fabrication of Flexible and High-Performing Thermoelectrics by Direct Laser Printing on Plastic Foil

The emerging fields of wearables and the Internet of Things introduce the need for electronics and power sources with unconventional form factors: large area, customizable shape, and flexibility. Thermoelectric (TE) generators can power those systems by converting abundant waste heat into electricity, whereas the versatility of additive manufacturing suits heterogeneous form factors. Here, additive manufacturing of high-performing flexible TEs is proposed. Maskless and large-area patterning of Bi2Te3-based films is performed by laser powder bed fusion directly on plastic foil. Mechanical interlocking allows simultaneous patterning, sintering, and attachment of the films to the substrate without using organic binders that jeopardize the final performance. Material waste could be minimized by recycling the unexposed powder. The particular microstructure of the laser-printed material renders the-otherwise brittle-Bi2Te3 films highly flexible despite their high thickness. The films survive 500 extreme-bending cycles to a 0.76 mm radius. Power factors above 1500 µW m-1K-2 and a record-low sheet resistance for flexible TEs of 0.4 Ω sq-1 are achieved, leading to unprecedented potential for power generation. This versatile fabrication route enables innovative implementations, such as cuttable arrays adapting to specific applications in self-powered sensing, and energy harvesting from unusual scenarios like human skin and curved hot surfaces.

Stamp-Like Energy Harvester and Programmable Information Encrypted Display Based on Fully Printable Thermoelectric Devices

Thermoelectric (TE) devices exhibit considerable application potential in Internet of Things and personal health monitoring systems. However, TE self-powered devices are expensive and their fabrication process is complex. Therefore, large-scale preparation of the TE devices remains challenging. In this work, simple screen-printing technology is used to fabricate a user-friendly and high-performance paper-based TE device, which can be used in both stamp-like paper-based TE generators and infrared displays. When used as a paper-based TE generator, an output power of 940.8 µW is achieved with a temperature difference of 40 K. The programmable infrared pattern based on the TE array display could be used to realize encryption and anti-counterfeiting properties. Moreover, a visual extraction algorithm is used to develop a mobile application for processing and decoding the infrared quick response code information. These findings offer an exciting approach to using paper-based TEGs in applications such as energy harvesting devices, optical encryption, anti-counterfeiting, and dynamic infrared display.

High Figure-of-Merit Telluride-Based Flexible Thermoelectric Films through Interfacial Modification via Millisecond Photonic-Curing for Fully Printed Thermoelectric Generators

The thermoelectric generator (TEG) shows great promise for energy harvesting and waste heat recovery applications. Cost barriers for this technology could be overcome by using printing technologies. However, the development of thermoelectric (TE) materials that combine printability, high-efficiency, and mechanical flexibility is a serious challenge. Here, flexible (SbBi)2 (TeSe)3 -based screen-printed TE films exhibiting record-high figure of merits (ZT) and power factors are reported. A high power factor of 24 µW cm-1  K-2 (ZTmax  ≈ 1.45) for a p-type film and a power factor of 10.5 µW cm-1  K-2 (ZTmax  ≈ 0.75) for an n-type film are achieved. The TE inks, comprised of p-Bi0.5 Sb1.5 Te3 (BST)/n-Bi2 Te2.7 Se0.3 (BT) and a Cu-Se-based inorganic binder (IB), are prepared by a one-pot synthesis process. The TE inks are printed on different substrates and sintered using photonic-curing leading to the formation of a highly conducting β-Cu2- δ Se phase that connects "microsolders," the grains resulting in high-performance. Folded TEGs (f-TEGs) are fabricated using the materials. A half-millimeter thick f-TEG exhibits an open-circuit voltage (VOC ) of 203 mV with a maximum power density (pmax ) of 5.1 W m-2 at ∆T = 68 K. This result signifies that a few millimeters thick f-TEG could power Internet-of-Things (IoTs) devices converting low-grade heat to electricity.

Photonic Curing Enables Ultrarapid Processing of Highly Conducting β-Cu2-δSe Printed Thermoelectric Films in Less Than 10 ms

It has been a challenge to obtain high electrical conductivity in inorganic printed thermoelectric (TE) films due to their high interfacial resistance. In this work, we report a facile synthesis process of Cu-Se-based printable ink for screen printing. A highly conducting TE β-Cu_2-δSe phase forms in the screen-printed Cu-Se-based film through ≤10 ms sintering using photonic-curing technology, minimizing the interfacial resistance. This enables overcoming the major challenges associated with printed thermoelectrics: (a) to obtain the desired phase, (b) to attain high electrical conductivity, and (c) to obtain flexibility. Furthermore, the photonic-curing process reduces the synthesis time of the TE β-Cu_2-δSe film from several days to a few milliseconds. The sintered film exhibits a remarkably high electrical conductivity of ∼3710 S cm^-1 with a TE power factor of ∼100 μW m^-1 K^-2. The fast processing and high conductivity of the film could also be potentially useful for different printed electronics applications.