Energy-harvesting from low-temperature environmental heat via thermoelectric generators (TEG) is a versatile and maintenance-free solution for large-scale waste heat recovery and supplying renewable energy to a growing number of devices in the Internet of Things (IoT) that require an independent wireless power supply. A prerequisite for market competitiveness, however, is the cost-effective and scalable manufacturing of these TEGs. Our approach is to print the devices using printable thermoelectric polymers and composite materials. We present a mass-producible potentially low-cost fully screen printed flexible origami TEG. Through a unique two-step folding technique, we produce a mechanically stable 3D cuboidal device from a 2D layout printed on a thin flexible substrate using thermoelectric inks based on PEDOT nanowires and a TiS2:Hexylamine-complex material. We realize a device architecture with a high thermocouple density of 190 per cm² by using the thin substrate as electrical insulation between the thermoelectric elements resulting in a high-power output of 47.8 µWcm−² from a 30 K temperature difference. The device properties are adjustable via the print layout, specifically, the thermal impedance of the TEGs can be tuned over several orders of magnitudes allowing thermal impedance matching to any given heat source. We demonstrate a wireless energy-harvesting application by powering an autonomous weather sensor comprising a Bluetooth module and a power management system.

Printed thermoelectrics (TE) could significantly reduce the production cost of energy harvesting devices by large-scale manufacturing. However, developing a high-performance printable TE material is a substantial challenge. In this work,...

High-performance Ag−Se-based n-type printed thermoelectric (TE) materials suitable for room-temperature applications have been developed through a new and facile synthesis approach. A high magnitude of the Seebeck coefficient up to 220 μV K −1 and a TE power factor larger than 500 μW m −1 K −2 for an n-type printed film are achieved. A high figure-of-merit ZT ∼0.6 for a printed material has been found in the film with a low in-plane thermal conductivity κ F of ∼0.30 W m −1 K −1 . Using this material for n-type legs, a flexible folded TE generator (flexTEG) of 13 thermocouples has been fabricated. The open-circuit voltage of the flexTEG for temperature differences of ΔT = 30 and 110 K is found to be 71.1 and 181.4 mV, respectively. Consequently, very high maximum output power densities p max of 6.6 and 321 μW cm −2 are estimated for the temperature difference of ΔT = 30 K and ΔT = 110 K, respectively. The flexTEG has been demonstrated by wearing it on the lower wrist, which resulted in an output voltage of ∼72.2 mV for ΔT ≈ 30 K. Our results pave the way for widespread use in wearable devices.

Additive manufacturing (AM) is a recent growing technology, which is currently implemented for different application fields, from rapid prototyping to cost-effective manufacturing of industrial components with complex shapes. Printable thermoelectric materials offer synergies with AM and can be integrated into 3D printed thermoelectric generators (TEGs). In this work, we have formulated an Ag 2 Se-based n-type printable thermoelectric (TE) ink with a high figure-of-merit of ∼1 at room temperature. Three scaffolds with different shapes have been printed using 3D printing. The developed ink as ntype legs and commercially available PEDOT as p-type legs were then painted on the 3D printed scaffolds to fabricate three TEGs with a different number of legs and shapes. The performance of the TEGs was studied for different temperature differences between ΔT = 10 and 70 K. Power output (P max ) levels of several microwatts and output voltages of several millivolts can be easily achieved.

The Cu2Te chalcogenide alloy is doped with 2 at. % Ni to increase the charge carrier concentration and then is further doped with 3 at. % Se to reduce the thermal conductivity. The alloys processing is kept simple–vacuum arc melting only to make a dense alloy for characterization. This also results in retaining the as-solidified highly layered structure. The alloys are found to have two polymorphic forms: hexagonal and orthorhombic at room temperature with a superstructure. The fractured surface shows clearly the layered structure with ∼300 nm thick platelet like features stacked together to form large defect free grains. The electrical conductivity increases to ∼7 × 103 S cm−1 due to Ni-doping compared to ∼5 × 103 S cm−1 for the undoped alloy at room temperature. This however decreases to ∼2.5 × 103 S cm−1 due to double doping, i.e., Ni and Se. In both cases, the alloys exhibit a weak metallic behavior with the conductivity decreasing with increasing temperature. The Seebeck coefficient however increases with temperature and with double doping resulting in the highest Seebeck coefficient, which increases from 40 μVK−1 to 110 μVK−1 when the temperature varies from 300 K to 1000 K. The hole carrier concentration in the two alloys, Ni-doped and double doped, is found to be nearly identical, 7 × 1020 cm−3 and 8.52 × 1020 cm−3, respectively, while the mobility of carriers decreased by 5 times from 283 cm2 V−1 s−1 to 52 cm2 V−1 s−1 due to double doping. These factors together with multiple scale phonon scattering resulted in the double doped alloy having the lowest thermal conductivity in the range of 1–2 Wm−1 K−1 in the complete temperature range. The thermal conductivity reduction due to the layered structure and alloy scattering results in increasing the figure of merit zT steeply to 0.65 at 950 K which at 1100 K can reach 1.0.

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The chemical composition of LiCoO, a layered oxide commonly used as electrode in batteries, was changed to LiCoNiO by a combination of substitution and lithiation to enhance the thermoelectric figure-of-merit at high temperatures. Substitution of Ni as well as lithiation does not change the crystal structure, R3̅m. The lattice parameters c and a are found to increase slightly but maintain a nearly constant ratio, 4.99, indicating no lattice distortion. The trivalent Co was substituted with divalent Ni to synthesize LiCoNiO series of p-type compounds with x varying up to 0.15. The high-temperature thermopower decreases drastically from ∼600 to 300 μV K, while the electrical resistivity drops by an order of magnitude from 1 × 10 to 1 × 10 Ω m due to substitution of 15 atom % Ni. The total thermal conductivity also decreases from ∼3 to 1.5 W m K. Increasing the amount of Li in LiCoNiO changes the thermophysical properties further and leads to enhancement of figure-of-merit. The power factor is found to change from 37.6 μW m K for the base compound to 120 μWm K, a significant improvement for a p-type compound. The overall figure-of-merit as a result increases to 0.12 at ∼1100 K due to substitution and lithiation, a giant increase of ∼760% compared to 1 × 10 for the pure compound LiCoO. These substituted and lithiated compounds are found to be extremely stable even after six months and exhibit totally reproducible thermophysical properties.

Enhancement of figure-of-merit due to band matching and bending at the half-Heusler/chalcogendie interfaces facilitating charge transport while blocking the phonons.