Room temperature aqueous-based synthesis of copper-doped lead sulfide nanoparticles for thermoelectric application

• A surfactant-free approach to produce Cu-doped PbS nanoparticles is presented. • Oxide removal via a reduction annealing process allows enhancing electrical conductivity. • Incorporation of Cu improvement of thermoelectric figure of merit is demonstrated. • A maximum ZT of 1.22 at 773 K with a record average ZT ave = 0.76 for Pb 0.955 Cu 0.045 S is achieved. A versatile, scalable, room temperature and surfactant-free route for the synthesis of metal chalcogenide nanoparticles in aqueous solution is detailed here for the production of PbS and Cu-doped PbS nanoparticles. Subsequently, nanoparticles are annealed in a reducing atmosphere to remove surface oxide, and consolidated into dense polycrystalline materials by means of spark plasma sintering. By characterizing the transport properties of the sintered material, we observe the annealing step and the incorporation of Cu to play a key role in promoting the thermoelectric performance of PbS. The presence of Cu allows improving the electrical conductivity by increasing the charge carrier concentration and simultaneously maintaining a large charge carrier mobility, which overall translates into record power factors at ambient temperature, 2.3 mWm -1 K −2 . Simultaneously, the lattice thermal conductivity decreases with the introduction of Cu, leading to a record high ZT = 0.37 at room temperature and ZT = 1.22 at 773 K. Besides, a record average ZT ave = 0.76 is demonstrated in the temperature range 320–773 K for n-type Pb 0.955 Cu 0.045 S.