MXene as charge reservoir promotes the thermoelectric performance of layered metal selenide SnSe2

Abstract

Layered metal selenides have attracted widespread attention in thermoelectrics. However, the thermoelectric performance of these compounds holding n-type conduction suffers from low electrical conductivity especially along out-of-plane direction mainly due to the carrier deficiency. Herein, two-dimensional MXene with metallic conductivity is introduced into SnSe2 matrix as a carrier reservoir to alleviate the electron shortage. Br-doped SnSe2/Ti3C2Tx composites are successfully fabricated by a hydrothermal method combined with solid-state synthesis. Compared with that of pristine SnSe2, the carrier concentration of SnSe1.97Br0.03/0.4 wt% Ti3C2Tx is enlarged by three orders of magnitude from 1017 cm–3 to 1020 cm–3. Meanwhile, it is revealed that the electrons transfer from the MXene layers into the SnSe2 matrix facilitated by elevated temperature based on the first-principles calculations. Combining with the intrinsically low lattice thermal conductivity, a peak zT close to unity is achieved along out-of-plane direction at 818 K in SnSe1.97Br0.03/0.4 wt% Ti3C2Tx sample. These findings offer an available strategy to efficiently increase the carrier concentration of wide-gap layered compounds.