![]() Unfortunately, barrier layer design remains a challenge since the interface between the barrier layer and the TE material should exhibit both high strength and low resistivity while ensuring long-term device stability at the service temperature, and the current lack of adequate barrier layers is a bottleneck limiting the application of TE devices in waste heat recovery 13, 14, 15. ![]() In the last two decades, significant breakthroughs have been made in improving the performance of TE materials 10, 11, 12. To prevent performance degradation or device failure caused by mutual diffusion between the TE materials and the electrodes during connection and service, it is essential to introduce a diffusion barrier layer on the surface of the TE materials 9. The conversion efficiency ( η) of TE devices is related to the dimensionless figure of merit ( ZT) of the constituent TE materials and the connection quality 6, 7, 8. The most common configuration of these TE devices is to connect p- and n-type TE legs with electrodes electrically in series and thermally in parallel 5. Additionally, there is great promise for the use of TE devices in low-grade waste heat recovery since more than 60% of the energy generated through burning fossil fuels is discharged into the environment as waste heat, about half of which is low-grade 4, for which there remains a lack of effective recycling methods. Thermoelectric (TE) devices that can convert thermal energy into electrical energy have been widely used in maintenance-free power supply systems for deep space exploration and other extreme environments 1, 2, 3. Highly competitive conversion efficiency of 6.2% and power density of 0.51 W cm −2 are achieved for a module with leg length of 2 mm at the hot-side temperature of 523 K, and no degradation is observed following operation for 360 h, a record for stable service at this temperature, paving the way for its application in low-grade waste heat recovery. A titanium barrier layer with loose structure is optimized, in which the low Young’s modulus and particle sliding synergistically alleviates interfacial stress, while the TiTe 2 reactant enables metallurgical bonding and ohmic contact between the barrier layer and the thermoelectric material, leading to a desirable interface characterized by high-thermostability, high-strength, and low-resistivity. ![]() Here we propose a new design principle of barrier layers beyond the thermal expansion matching criterion. The lack of desirable diffusion barrier layers currently prohibits the long-term stable service of bismuth telluride thermoelectric devices in low-grade waste heat recovery.
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