Researchers from the Technical University of Darmstadt and the Karlsruhe Institute of Technology (KIT) have achieved a significant breakthrough in flexible energy harvesting by developing fully screen-printed 3D thermoelectric generators (TEGs) with a 3D multi-layer architecture, capable of milliwatt-scale power output. Their work, published in Energy & Environmental Science, demonstrates a scalable additive manufacturing process that overcomes key limitations of traditional TEGs, paving the way for their use as sustainable battery replacements in wearables and IoT devices.
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Powering IoT sustainably
The growing ecosystem of low-power electronics, from wearable health monitors to industrial IoT sensors, relies heavily on lithium-ion batteries. Their production depends on finite resources, and their disposal creates significant electronic waste. TEGs, which convert waste heat directly into electricity, offer a promising alternative. However, conventional TEGs made from brittle bulk materials are expensive, rigid, and difficult to customize, limiting their widespread adoption.
Printed inks for flexible devices
The research team turned to additive screen printing, a mature and scalable manufacturing technique, to address these challenges. Their innovative process involves the layer-by-layer printing of electrodes, carbon interlayers, and thermoelectric legs to build a complete 3D device.
The team formulated specialized inks using n-type silver selenide (Ag₂Se) and p-type bismuth antimony telluride (Bi₀.₅Sb₁.₅Te₃). A critical innovation was the use of a carbon-based interface layer, which drastically reduced the electrical contact resistance between the TE materials and the electrodes, a major hurdle in printed electronics. Furthermore, they employed an additive printing strategy, depositing multiple layers of the TE inks to achieve a thickness of over 600 micrometers, which is essential for maintaining a significant temperature gradient across the device.
“By combining interface engineering with multi-layer additive printing, we have successfully overcome the two main obstacles for high-performance printed TEGs: high contact resistance and limited leg thickness,” said Professor Uli Lemmer, a corresponding author of the study.
The team fabricated two devices with different numbers of thermocouples. The flagship device, print-TEG II, incorporating 50 thermocouples, delivered groundbreaking performance; a maximum power output (P_max) of 1.22 milliwatts (mW), an open-circuit voltage (V_OC) of 268 mV, and a power density of 67 µW cm⁻² (or >400 µW g⁻¹).
This was achieved at a relatively low temperature difference (ΔT) of just 43 K, equivalent to the heat from a warm surface to ambient air. This is the highest power output ever reported for a fully printed planar TEG, moving the technology from the microwatt into the practical milliwatt range needed for many real-world applications.
Prospects for scalable and cost-effective manufacturing
Beyond performance, the study highlighted the method’s scalability and cost-effectiveness. A detailed cost analysis estimated the material cost of one print-TEG II device at approximately €1.45, with potential for further reduction through geometric optimization. The screen-printing process is inherently compatible with high-throughput roll-to-roll manufacturing, essential for mass production. The cost could be further reduced by optimizing the device geometry; the researchers found that making the p-type legs narrower than the n-type legs could boost power density by 39% while using less material.
The devices also showed excellent operational stability over 30 continuous cycles and were demonstrated in a wearable scenario, generating 36 mV from a mere 5 K temperature difference between the human arm and a heat sink.
A step toward sustainable electronics
This research marks a pivotal step forward. By proving that screen-printed TEGs can generate sufficient power for low-energy devices, the team has positioned them as a serious, sustainable alternative to batteries. This technology promises to reduce e-waste and harness the vast amounts of unused low-grade waste heat, ultimately enabling a new generation of self-powered, maintenance-free electronic systems.
3D printing’s role in next-generation energy devices
This breakthrough builds on a wider body of research exploring how additive manufacturing is reshaping the way energy devices are produced. Earlier this year, researchers highlighted how 3D printing transforms energy technologies across generation, conversion, and storage, from solar panels to solid-state batteries. More recently, a review of 3D printed lattice structures for thermoelectric devices emphasized how design freedom can boost efficiency by decoupling thermal and electrical properties. Together, these developments point to a growing convergence between functional materials and advanced manufacturing in the energy sector.
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Featured image shows a schematic representation of print-TEG fabrication steps using screen printing. Image via Energy & Environmental Science / TU Darmstadt, KIT.
