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Nat Mater. 2015 Jun;14(6):622-7. doi: 10.1038/nmat4251. Epub 2015 Apr 6.

Flexible n-type thermoelectric materials by organic intercalation of layered transition metalĀ dichalcogenide TiS2.

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1] Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan [2] State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China.
Department of Mechanical Engineering, University of Colorado, Boulder, Colorado 80309, USA.
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan.
College of Material Science and Engineering, Nanjing University of Technology, Nanjing 210009, China.
KOBELCO Research Institute, Kobe, Hyogo 651-2271, Japan.
Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA.


Organic semiconductors are attracting increasing interest as flexible thermoelectric materials owing to material abundance, easy processing and low thermal conductivity. Although progress in p-type polymers and composites has been reported, their n-type counterpart has fallen behind owing to difficulties in n-type doping of organic semiconductors. Here, we present an approach to synthesize n-type flexible thermoelectric materials through a facile electrochemical intercalation method, fabricating a hybrid superlattice of alternating inorganic TiS2 monolayers and organic cations. Electrons were externally injected into the inorganic layers and then stabilized by organic cations, providing n-type carriers for current and energy transport. An electrical conductivity of 790 S cm(-1) and a power factor of 0.45 mW m(-1) K(-2) were obtained for a hybrid superlattice of TiS2/[(hexylammonium)x(H2O)y(DMSO)z], with an in-plane lattice thermal conductivity of 0.12 Ā± 0.03 W m(-1) K(-1), which is two orders of magnitude smaller than the thermal conductivities of the single-layer and bulk TiS2. High power factor and low thermal conductivity contributed to a thermoelectric figure of merit, ZT, of 0.28 at 373 K, which might find application in wearable electronics.


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