Abstract
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 ± 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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Acknowledgements
The authors thank R. Sasai for polarized FTIR measurements. C.W. acknowledges financial support from a Murata Science Foundation Research Grant, a Thermal and Electrical Energy Technology Foundation Research Grant, Takahashi Industrial and Economic Research Foundation and JSPS KAKENHI Grant Number 26820295. K.Koumoto acknowledges financial support from JSPS KAKENHI Grant Number 25289226 and TherMAT. G.J.S. acknowledges support from AFOSR-MURI and DOE-EFRC (S3TEC) award number DE-SC0001299. X.G. and R.Y. acknowledge the partial support for this work from the NSF CAREER award (0846561) and AFOSR (FA9550-11-1-0109). The simulation work used the Janus supercomputer, supported by NSF (0821794).
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C.W. and K.Koumoto initiated the concepts. C.W. designed the experiments. C.W., F.D., T.I., Y.W., H.S., M.K., K.Koga and K.Y. conducted the experiments. X.G. and R.Y. performed the molecular dynamics simulations. C.W., X.G., G.J.S., R.Y. and K.Koumoto analysed the data and wrote the manuscript. All of the authors contributed to manuscript preparation.
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Wan, C., Gu, X., Dang, F. et al. Flexible n-type thermoelectric materials by organic intercalation of layered transition metal dichalcogenide TiS2. Nature Mater 14, 622–627 (2015). https://doi.org/10.1038/nmat4251
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DOI: https://doi.org/10.1038/nmat4251
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