Flexible n-type thermoelectric materials by organic intercalation of layered transition metal dichalcogenide TiS 2

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 dificulties 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 0.45mWm^-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±0.03Wm^-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.