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

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 SnSe ₂ matrix as a carrier reservoir to alleviate the electron shortage. Br-doped SnSe ₂/Ti ₃C ₂T _x composites are successfully fabricated by a hydrothermal method combined with solid-state synthesis. Compared with that of pristine SnSe ₂, the carrier concentration of SnSe _1.97Br _0.03/0.4 wt% Ti ₃C ₂T _x is enlarged by three orders of magnitude from 10 ¹⁷ cm ^–3 to 10 ²⁰ cm ^–3 . Meanwhile, it is revealed that the electrons transfer from the MXene layers into the SnSe ₂ 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 SnSe _1.97Br _0.03/0.4 wt% Ti ₃C ₂T _x sample. These findings offer an available strategy to efficiently increase the carrier concentration of wide-gap layered compounds.