Flexible Thermoelectric Materials and Generators: Challenges and Innovations

Abstract

The urgent need for ecofriendly, stable, long‐lifetime power sources is driving the booming market for miniaturized and integrated electronics, including wearable and medical implantable devices. Flexible thermoelectric materials and devices are receiving increasing attention, due to their capability to convert heat into electricity directly by conformably attaching them onto heat sources. Polymer‐based flexible thermoelectric materials are particularly fascinating because of their intrinsic flexibility, affordability, and low toxicity. There are other promising alternatives including inorganic‐based flexible thermoelectrics that have high energy‐conversion efficiency, large power output, and stability at relatively high temperature. Herein, the state‐of‐the‐art in the development of flexible thermoelectric materials and devices is summarized, including exploring the fundamentals behind the performance of flexible thermoelectric materials and devices by relating materials chemistry and physics to properties. By taking insights from carrier and phonon transport, the limitations of high‐performance flexible thermoelectric materials and the underlying mechanisms associated with each optimization strategy are highlighted. Finally, the remaining challenges in flexible thermoelectric materials are discussed in conclusion, and suggestions and a framework to guide future development are provided, which may pave the way for a bright future for flexible thermoelectric devices in the energy market.

High‐Performance Thermoelectric SnSe: Aqueous Synthesis, Innovations, and Challenges

“…Flexible thermoelectric generators are receiving increasing attention due to their capability of directly converting heat into electricity through conformably attaching onto heat sources 336,337. Different from solid thermoelectric modules from which the main components are bulk materials, flexible thermoelectric generator with a high flexibility is made of thermoelectric materials with a much smaller average size to ensure the flexibility, and hydrothermal/solvothermal‐based solution routes are key answers to solve this issues through convenient morphology control by adjusting appropriate kinetic conditions during synthesis.…”

“…To achieve a potentially high performance in SnSe‐based flexible thermoelectric generators, the materials should have much low dimensions to ensure the quantum confinement effect 336. The quantum confinement refers to when the dimensions of nanocrystals reduce to a certain degree, the nanosized crystals with different sizes can exhibit different bandgap values (normally higher than the larger‐sized crystals) between the conduction band and the valence band, thus have unique electronic properties that differ from larger crystals.…”

Emerging Materials and Strategies for Personal Thermal Management

“…Flexible TEDs have been integrated into textile for power generations, like knitted TED, woven glass fabric, 1D and 2D TEDs. [ 29 ] A worthy‐mentioned particular example is shown in Figure 9 A, in which Lee et al fabricated a flexible TE textile based on electrospun polymer nanofiber cores coated with n‐ and p‐type semiconductor sheaths (Bi 2 Te 3 and Sb 2 Te 3 ) and twisted into flexible yarns. [ 135 ] Then they wove the yarns into garter‐stitch, zigzag‐stitch, and plain‐weave TE textiles for power generation.…”

Anisotropy Control–Induced Unique Anisotropic Thermoelectric Performance in the n‐Type Bi2Te2.7Se0.3 Thin Films

“…κ can be treated as the accumulation of lattice vibration (lattice thermal conductivity, κ l ) and electrical thermal conductivity (κ e ) . In recent decades, flexible thermoelectrics show extensive potential for application in wearable electronics due to high flexibility comparing with their bulk counterparts . For example, with high flexibility, thin thermoelectric films can conveniently attach on human skin, which shows great potentials to utilize the temperature gradient between human body and surrounding environment to generate electricity to charge cell phones .…”