Wearable and flexible thermoelectrics for energy harvesting
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Introduction Conjugated polymers hold great promise for harvesting thermal energy at temperatures below 200°C. Their light and flexible nature and possibility of scalable processing such as roll-toroll or inkjet printing make them ideally suited for powering wearable electronics that are impractical with rigid inorganic materials. However, the electrical conductivity and Seebeck coefficient of conjugated polymers need to be significantly enhanced to meet the requirements of such applications. Tremendous effort has been made to enhance their power factor (PF = S2 σ, where S is the Seebeck coefficient and σ is the electrical conductivity) over the past two decades. Aside from adjusting the oxidation level and molecular arrangement, hybridization offers a facile approach to developing both p- and n-type flexible thermoelectric materials with enhanced performance. In this article, we focus on recent progress in hybrid thermoelectric composites. We discuss synthesis techniques and key parameters that influence thermoelectric properties. A flexible organic-based thermoelectric module from Fujifilm is discussed along with the fabrication of high-quality carbon nanotubes (CNTs) paste. In addition, we highlight a recent breakthrough in the fabrication of inorganic–organic hybrid
superlattices for the application of wearable/flexible thermoelectric devices at temperatures below 100°C.
Organic thermoelectric materials and their hybrid composites Conjugated polymers Typical conjugated polymers used as thermoelectric materials include poly(3,4-ethylenedioxythiophene) (PEDOT), polyanilines (PANIs), polythiophenes, polyacetylenes, polypyrrole, and polycarbazole, which have been intensively studied and reviewed.1–5 Among these, p-type PEDOT:PSS (polystyrene sulfonate) and PEDOT-Tos (Tosylate) exhibit encouraging thermoelectric performance through careful chemical control of the oxidation level where the optimal power factor (PF) can reach 460 and 450 μW/mK2,6,7 and the values are among the highest PF values that the organic-based thermoelectric materials can achieve. However, air-stable n-type organic conductors are rare as most of them have relatively small electron affinity and are likely to react with water and oxygen.8–10 Recently, it was found that electrochemical polymerization can be used to synthesize high-performance n-type conjugated polymers by controlling the oxidation (and thus the carrier concentration) at the anode. For instance, Sun et al. fabricated
Ruoming Tian, Toyota Physical and Chemical Research Institute, Japan; [email protected] Chunlei Wan, School of Materials Science and Engineering, Tsinghua University, China; [email protected] Naoyuki Hayashi, Fujifilm Corporation, Japan; [email protected] Toshiaki Aoai, Chiba University, Japan; [email protected] Kunihito Koumoto, Toyota Physical and Chemical Research Institute, Japan; [email protected] doi:10.1557/mrs.2018.8
• VOLUME • MARCH © 2018 Materials Research Society BULLETIN 43use, 2018at• Downloaded from https://www.cambr
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