Interfacial engineering effect and bipolar conduction of Ni- doped MoS2 nanostructures for thermoelectric application

Transition Metal Chalcogenides play an important role in the thermoelectric (TE) application due to their unique properties such as stability, easily tunable carrier transport and charge carrier mobility which enhance the power factor. Molybdenum disulphide (MoS2) is a hopeful TE material with a layered structure, but it possesses low electrical conductivity. Herein, our present work focuses to improve the electrical conductivity of MoS2 by Ni-doping and the effect of Ni-concentration was studied extensively. Undoped and Ni-doped MoS2 samples were successfully prepared by hydrothermal route. The hexagonal structured 2HMoS2 and the formation of nickel sulphide (NiS) secondary phase at 10 at% of Ni-concentration was confirmed by XRD analysis. HRTEM confirmed the influence of Ni content in MoS2 layers which create the bonding between the layers and reduces the interlayer distance of MoS2. The reduced thermal conductivity was observed around 0.48 Wm-1K-1 for 7.5 at% of Ni-doped MoS2 which is two times lower than that of undoped MoS2. Meanwhile, the enhancement of electrical conductivity of Ni-doped samples from 0.012 S/ cm to 0.049 S/cm observed for 7.5 at% of Ni-doped MoS2 sample. Because of NiS, the conduction behavior was changed from p-type to n-type Seebeck coefficient. The maximum zT was obtained as 0.28 x 10-3 for undoped sample. However, Ni-doping was experimentally proved to the simultaneous optimization of enhanced electrical conductivity and the suppressed thermal conductivity, the change in carrier type due to nickel sulphide (NiS) phase reduced the figure of merit.