Mechanistic Insight into the Effect of Cu Doping on Thermoelectric Properties of Sintered Wet-Chemically Synthesized SnSe₂ Nanosheets

SnSe2─an uncommon, sustainable n-type thermoelectric material─has previously been doped with elements including Cu to improve its thermoelectric figure of merit, ZT value. However, the effects and mechanisms behind Cu doping remain unclear. To provide important mechanistic insight, SnSe2:Cu nanosheets were synthesized, sintered, and subjected to multifaceted analysis using a variety of analytical techniques. The results suggested that intercalated Cu+ ions contribute to the density of states of the valence band, shifting the Fermi energy toward the conduction band. The carrier concentration was raised, causing a shift to conduction across two conduction band minima. Additionally, a change to ionized impurity scattering dominated carrier mobility meant a high mobility at high temperatures, since electron–phonon interactions were insignificant. The result was a significantly increased electrical conductivity, while the thermal conductivity decreased due to scattering at nanosheet grain boundaries and Cu+ ions. High ZT values of 0.2 in the in-plane, and 0.6 in the out-of-plane directions were achieved at 667 K.