Chemical Welding on Semimetallic TiS₂ Nanosheets for High-Performance Flexible n-Type Thermoelectric Films

Solution-based processing of two-dimensional (2D) materials provides the possibility of allowing these materials to be incorporated into large-area thin films, which can translate the interesting fundamental properties of 2D materials into available devices. Here, we report for the first time a novel chemical-welding method to achieve high-performance flexible n-type thermoelectric films using 2D semimetallic TiS₂ nanosheets. We employ chemically exfoliated TiS₂ nanosheets bridged with multivalent cationic metal Al³⁺ to cross-link the nearby sheets during the film deposition process. We find that such a treatment can greatly enhance the stability of the film and can improve the power factor by simultaneously increasing the Seebeck coefficient and electrical conductivity. The resulting TiS₂ nanosheet-based flexible film shows a room temperature power factor of ∼216.7 μW m^-1 K^-2, which is among the highest chemically exfoliated 2D transition-metal dichalcogenide nanosheet-based films and comparable to the best flexible n-type thermoelectric films, to our knowledge, indicating its potential applications in wearable electronics.