MXene Nanosheet/Organics Superlattice for Flexible Thermoelectrics

Two-dimensional (2D) materials with outstanding electronic transport properties are rigid against bending because of strong in-plane covalent bonding and intrinsically flexible because of the lack of out-of-plane constraint and thus are considered to be promising for flexible thermoelectrics (TEs). As a typical 2D material, MXene, however, exhibited a restricted TE performance because the termination groups and guest molecules in MXene nanosheets introduced by acid etching and reassembly deteriorate intra/interflake conduction. This work realized increases in both the carrier concentration and intra/interflake mobility by the construction of a MXene nanosheet/organic superlattice (SL) and composition engineering, attributed to electron injection, intercoupling strengthening, and defect reduction at the nanosheet edges. An electrical conductivity increased by 5 times, to 2.7 × 105 S m-1, led to power factors of up to ∼33 μW m-1 K-2, which is above the state-of-the-art for similar materials, almost by a factor of 10. A TE module comprising four SL film legs could yield 58.6 nW power at a temperature gradient of 50 K. Additionally, both the annealed film and the corresponding module exhibited excellent reproducibility and stability. Our results provide a strategy to tailor the TE performance of 2D-material films through SL construction and composition engineering.