Screen printing allows for direct conversion of thermoelectric nanocrystals into flexible energy harvesters and coolers. However, obtaining flexible thermoelectric materials with high figure of merit ZT through printing is an exacting challenge due to the difficulties to synthesize high-performance thermoelectric inks and the poor density and electrical conductivity of the printed films. Here, we demonstrate high-performance flexible films and devices by screen printing bismuth telluride based nanocrystal inks synthesized using a microwave-stimulated wet-chemical method. Thermoelectric films of several tens of microns thickness were screen printed onto a flexible polyimide substrate followed by cold compaction and sintering. The n-type films demonstrate a peak ZT of 0.43 along with superior flexibility, which is among the highest reported ZT values in flexible thermoelectric materials. A flexible thermoelectric device fabricated using the printed films produces a high power density of 4.1 mW/cm2 with 60 °C temperature difference between the hot side and cold side. The highly scalable and low cost process to fabricate flexible thermoelectric materials and devices demonstrated here opens up many opportunities to transform thermoelectric energy harvesting and cooling applications.

10Given increasing energy use as well as decreasing fossil fuel sources worldwide, it is no 11 surprise that interest in promoting energy efficiency through waste heat recovery is also 12 increasing. Thermoelectric generators (TEGs) are one of the most promising pathways 13 for waste heat recovery. Despite recent thermoelectric efficiency improvement in 14 nanostructured materials, a variety of challenges have nevertheless resulted in few 15 demonstrations of these materials for large-scale waste heat recovery. Here we 16 demonstrate a high-performance TEG by combining high-efficiency nanostructured bulk 17 materials with a novel direct metal brazing process to increase the device operating 18 temperature. A unicouple device generates a high power density of 5.26 W·cm -2 with a 19 500 °C temperature difference between hot and cold sides. A 1 kW TEG system is 20 experimentally demonstrated by recovering the exhaust waste heat from an automotive 21 diesel engine. The TEG system operated with a 2.1% heat-to-electricity efficiency under 22 the average temperature difference of 339 °C between the TEG hot-and cold-side 23 2 surfaces at a 550 °C exhaust temperature. The high-performance TEG reported here open 24 up opportunities to use TEGs for energy harvesting and power generation applications. 25

Printing is a versatile method to transform semiconducting nanoparticle inks into functional and flexible devices. In particular, thermoelectric nanoparticles are attractive building blocks to fabricate flexible devices for energy harvesting and cooling applications. However, the performance of printed devices are plagued by poor interfacial connections between nanoparticles and resulting low carrier mobility. While many rigid bulk materials have shown a thermoelectric figure of merit ZT greater than unity, it is an exacting challenge to develop flexible materials with ZT near unity. Here, a scalable screen-printing method to fabricate high-performance and flexible thermoelectric devices is reported. A tellurium-based nanosolder approach is employed to bridge the interfaces between the BiSbTe particles during the postprinting sintering process. The printed BiSbTe flexible films demonstrate an ultrahigh room-temperature power factor of 3 mW m −1 K −2 and ZT about 1, significantly higher than the best reported values for flexible films. A fully printed thermoelectric generator produces a high power density of 18.8 mW cm −2 achievable with a small temperature gradient of 80 °C. This screen-printing method, which directly transforms thermoelectric nanoparticles into high-performance and flexible devices, presents a significant leap to make thermoelectrics a commercially viable technology for a broad range of energy harvesting and cooling applications.

Lin et al. report 2D layered materials as a soft template for symmetry-mismatched epitaxial growth of PbSe/Bi2Se3 heterostructures.

Multifunctional sensors with integrated multiple sensing capabilities have enormous potential for in situ sensing, structural health monitoring, and wearable applications. However, the fabrication of multimodal sensors typically involves complex processing steps, which limit the choices of materials and device form factors. Here, an aerosol jet printed flexible bimodal sensor is demonstrated by using graphene and Ti 3 C 2 T x MXene nanoinks. The sensor can detect strain by measuring a change in the AC resistive voltage while simultaneously monitoring temperature by detecting the DC Seebeck voltage across the same printed device pattern. The printed bimodal sensor not only expands the sensing capability beyond conventional single-modality sensors but also provides improved spatial resolution utilizing the microscale printed patterns. The printed temperature sensor shows a competitive thermopower output of 53.6 μV/°C with ultrahigh accuracy and stability during both steady-state and transient thermal cycling tests. The printed sensor also demonstrates excellent flexibility with negligible degradations after 1000 bending cycles. The aerosol jet printing and integration of nanomaterials open many opportunities to design and manufacture multifunctional devices for a broad range of applications.