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.
