Thermoelectric performance of Cu₂Se doped with rapidly synthesized gel-like carbon dots

As an earth-abundant, inexpensive and non-toxic compound, Copper Selenide (Cu₂Se) is a frequently investigated material for thermoelectric (TE) conversion applications. In this research, stoichiometric Cu₂Se compounds were systematically doped with gel-like Carbon Dots (CDs), that were fabricated using a rapid and straightforward solvothermal method, at weight ratios of 2, 5 and 10%. The resultant ingots were spark plasma sintered and their TE performance was characterized. Scanning electron microscopy (SEM), energy dispersive X-Ray spectroscopy (EDX) and powder X-ray diffraction (PXRD) were used to correlate the microstructure to the TE properties. Based on these measurements, CD doping strategy on Cu₂Se yielded highly compacted, single phase grains with minimal oxidation. Characterization demonstrated a continuous enhancement of TE figure of merit (ZT) to a maximum of 2.1 at the optimum dopant ratio of 2 wt %. This enhancement was mainly due to the energy filtering effect of CD interfaces along the grain boundaries, and phonon scattering which increased the Seebeck coefficient and reduce the thermal conductivity. Doping beyond 2 wt% was recorded to inhibit this improvement. This research paved the path towards broader utilization of rapidly fabricated CDs to enhance TE conversion performance.