Thermally evaporated Cu _{2− <i>x</i>} Se thin films embedded with PbSe nanoinclusions: a multiphase system for thermoelectric applications

Thermoelectric (TE) devices pave a promising pathway for clean and efficient energy conversion between heat and electricity. Among various TE materials, copper selenide (Cu₂Se) has attracted significant interest due to its high electrical conductivity and low thermal conductivity offered by its superionic behavior, making it a candidate for high-performance thermoelectric applications. The present study systematically investigates the TE properties of thin film-based nanocomposites comprised of lead (Pb)-doped Cu_(2-<i>x</i>)Se integrated with lead selenide (PbSe) samples. XPS analysis infers the incorporation of Pb and reveals changes in the oxidation states and bonding environments of Cu and Se. Thermoelectric measurements in the temperature range of 300 K to 400 K demonstrate that Pb incorporation influences charge carrier transportation, as inferred alteration in the Seebeck coefficient and electrical conductivity. A slightly overestimated value of the figure-of-merit (<i>ZT</i>) has been evaluated by merely relying on the electronic thermal conductivity (<i>k</i> _e) and ignoring the lattice thermal conductivity (<i>κ</i> _l). This work reveals the importance of multiphase compositions in tuning of TE properties and suggests a route for deeper understanding of transport mechanisms in thin film samples.