ronment without mechanical parts, longlasting, maintenance-free, portable, etc. Therefore, TEGs are especially suitable for applications in self-powered electronic systems. [4][5][6] Most high-performance TE materials are inorganic semiconductors, which show high figure of merit values [7,8] and have irreplaceable applications as power supply systems in space exploration, such as radioisotope TE generators. [9,10] Nevertheless, traditional inorganic TE materials are mechanically rigid and fragile, thus are not compatible with heat sources with complex surfaces, obstructing their applications in distributed power supply systems, especially wearable electronics.Two main strategies have been developed to address these issues. One strategy used intrinsically flexible TE materials, including conducting polymers, [11][12][13] carbon-based materials, [14,15] and highly plastic semiconductors. [16,17] Despite these attractive developments, the intrinsically flexible TE materials still suffered inferior TE properties, and the TEGs based on these films were usually constructed using in-plane configurations that made them difficult to build matched thermal impedance when harvesting heat from human body. Quite recently, ionic TE materials as another candidate for thermal energy conversion, showed a magnitude larger temperature gradient driven voltage based on Soret effect than typical electronic TE materials based on electrons/holes diffusion. [18,19] However, most of the ionic TEGs only functioned Direct energy conversion based on thermoelectric (TE) materials is a longterm and maintenance-free energy harvesting technique, and therefore is very promising for self-powered wearable electronics. Yet, it is challenging to achieve high-performance stretchable, healable, and even recyclable thermoelectric generators (TEGs) without compromising TE conversion performance due to the intrinsic mechanical rigidity and brittleness of the inorganic TE materials. Herein, recyclable, healable, and stretchable TEGs (RHS-TEGs) are reported that are assembled from commercial Bi 2 Te 3 and Sb 2 Te 3 TE legs generating superior power density via the use of liquid metal as interconnects and dynamic covalent thermoset polyimine as encapsulation. The TEGs fabricated using this strategy are endowed with excellent TE performance, mechanical compliance, and healing and recycling capabilities. The normalized output power density and mechanical stretchability can reach up to 1.08 µW cm −2 •K 2 and 50%, respectively. After healing and recycling, the TEGs show output performance comparable to the original devices. The TEGs also exhibit high reliability and stability under cyclic deformation. This study paves the way for sustainable application of TEGs as energy harvesters to power wearable electronics using body heat.
A flexible active dual-parameter sensor for sensitive temperature and physiological signal monitoring has been developed via integrating thermoelectric and piezoelectric conversion.
suitable for BodyNET applications. Consequently, it is urgent to exploit lightweight TEGs with stretching and/or deformation capability that can be suitably attached to non-planar heat source surfaces without compromising generating performance. To achieve this goal, organic thermoelectric materials [6,7] and novel thermoelectric materials such as carbon nanotubes (CNTs) [8] with high flexibility are of great potential application, while this kind of materials still suffered inferior thermoelectric properties with low figure-of-merit (ZT) value and electrical conductivity. As a result, to attain excellent output performance of flexible TEGs, the use of highperformance inorganic thermoelectric materials is a sensible solution. Nevertheless, the mechanically rigid or fragile features obstruct their applications in wearable electronics.One direct and effective solution is based on the island-bridge type electric connection to realize flexibility for rigid high-performance inorganic materials, where bulk n-type and p-type materials are integrated using wavy serpentine copper wires, [9,10] liquid metal, [11][12][13] and so on. However, the output power of TEGs is still limited by the small temperature difference between body and the ambient, which is generally about 10 °C with only 1-2 °C built on thermoelectric legs. [14] This hinders the development of wearable devices. Besides, further improvement of specific power density is of equal importance for wearable applications. Thin-film TEGs fabricated on flexible substrate with low thickness and weight can easily adhere to soft skin to harvest body heat. [15,16] Nevertheless, the heat transfer along the thermoelectric legs is commonly Thermoelectric generators (TEGs) as potential power supply have great prospects for wearable application. Nevertheless, difficulties in realizing deformability, ultralight weight, and high power density of TEGs at the same time has strongly frustrated their commercial applications to date. Herein, inspired by the art of kirigami, an innovative design to construct stretchable, deformable, ultralight 3D thin-film TEG from a 2D structure by introducing rational kirigami cuts is proposed. Meanwhile, high-performance inorganic thermoelectric films are compatibly introduced to the TEG without property degradation. In addition, the vertical heat flow is easily realized in the planar thin-film TEG, which is beneficial for the establishment of large temperature differences. The fabricated ultralight kirigami-based TEG (only 29 mg in weight), without an additional heat sink demonstrates the highest open voltage density of 6.712 V g −1 with a maximum power density of 255.395 µW g −1 at T hot = 60 °C. Moreover, the TEG exhibits excellent compliance to extreme mechanical deformation and adaptability to variety surfaces. This work provides a new design concept for deformable TEGs with promising application in a broader set of BodyNET technology.
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