Stretchable Thermoelectric Generators Metallized with Liquid Alloy

Abstract

Conventional thermoelectric generators (TEGs) are normally hard, rigid, and flat. However, most objects have curvy surfaces, which require soft and even stretchable TEGs for maximizing efficiency of thermal energy harvesting. Here, soft and stretchable TEGs using conventional rigid BiTe pellets metallized with a liquid alloy is reported. The fabrication is implemented by means of a tailored layer-by-layer fabrication process. The STEGs exhibit an output power density of 40.6 μW/cm at room temperature. The STEGs are operational after being mechanically stretched-and-released more than 1000 times, thanks to the compliant contact between the liquid alloy interconnects and the rigid pellets. The demonstrated interconnect scheme will provide a new route to the development of soft and stretchable energy-harvesting avenues for a variety of emerging electronic applications.

Numerical modeling of the performance of thermoelectric module with polydimethylsiloxane encapsulation

“…In FVM, the physical domains of the TEM, including the regions of thermoelectric legs, PDMS encapsulation, solder layer, and copper strips, are divided by non-overlapping control volumes (CVs), as shown in Figure 4A. So, the CVs of these domains (1, 3, 12 and 4, 6, 8, 10) can have larger Δy than that of thermoelectric legs (5,9) and PDMS encapsulation (2,7,11). 24 The CVs have the same length in the x direction and different lengths in the y direction, which are marked as Δx and Δy, respectively.…”

“…For example, because the copper strips and solder layers have much greater k and γ, the temperature and voltage differences in these domains should be small. So, the CVs of these domains (1, 3, 12 and 4, 6, 8, 10) can have larger Δy than that of thermoelectric legs (5,9) and PDMS encapsulation (2,7,11).…”

“…4,5 Further, due to low thermal conductivity (0.23 Wm −1 K −1 ) of PDMS, 4 the thermal resistance introduced by PDMS encapsulation will block the heat transfer through the encapsulation components. 4,5 Further, due to low thermal conductivity (0.23 Wm −1 K −1 ) of PDMS, 4 the thermal resistance introduced by PDMS encapsulation will block the heat transfer through the encapsulation components.…”

“…Greek: α, Seebeck coefficient (V K −1 ); γ, electrical conductivity (S m −1 ); τ, Thomson coefficient (V K −1 ); θ, relaxation coefficient; λ, thermal diffusivity (m 2 s −1 ); ρ, density (kg m −3 ); η, efficiency (%) Subscripts: e, w, n, s, control interfaces; P, E, W, N, S, control volumes; cold, cold side of the TEM; hot, hot side of the TEM; OC, open circuit used as the encapsulation material to provide a flexible support for the thermoelectric legs when TEG was subjected to external stress and/or vibration. 4,5 Further, due to low thermal conductivity (0.23 Wm −1 K −1 ) of PDMS, 4 the thermal resistance introduced by PDMS encapsulation will block the heat transfer through the encapsulation components. Then, the heat harvesting could be concentrated in the region of thermoelectric legs, which is beneficial for the voltage generation.…”

Design of Substrate Stretchability Using Origami-Like Folding Deformation for Flexible Thermoelectric Generator

“…However, a flexible TE generator is required as there is frequently a need to attach generators to a heat source with a non-flat surface, such as piping or the human body. Recently, TE generators with bendability [3,4,5,6,7,8,9,10,11,12] and/or stretchability [13] were developed by using a deformable TE element (e.g., a carbon nanotube (CNT)-polystyrene (PS) composite) or a rubber-based stretchable substrate (e.g., polydimethylsiloxane (PDMS)). However, deformable TE conversion materials based on polymer composites unfortunately have inferior TE conversion efficiency compared to the rigid BiTe-based TE conversion materials, while the stretchable substrates using rubber have a narrow usable temperature range of 213–423 K [14].…”