High Power Factor and Thermoelectric Figure of Merit in Sb₂Si₂Te₆ through Synergetic Effect of Ca Doping

We report here a high thermoelectric performance in cadmium doped Sb2Si2Te6. The substitution of Ca2+ for Sb3+ provides a synergetic effect on the electrical transport properties, including hole concentration enhancement, valence band maximum flatting, band gap increase, and density of states effective mass enhancement in Sb2Si2Te6. Such effect leads to the highest power factor of 13.5 μW m–1 K–2 at 573 K and average power factor of 12.6 μW m–1 K–2 for Sb1.97Ca0.03Si2Te6. Such enhanced power factor and average power factor are ∼30% and ∼26% higher than that of pristine Sb2Si2Te6 respectively, which is very necessary for the output power optimization of Sb2Si2Te6. In addition, Ca doping also induces extra point defects phonon scattering, leading to a lowest lattice thermal conductivity of ∼0.41 W m–1 K–1 at 823 K for Sb1.99Ca0.01Si2Te6, ∼15% lower than that of pristine Sb2Si2Te6. The simultaneous optimization in power factor and lattice thermal conductivity enables us to achieve a high peak thermoelectric figure of merit ZT of ∼1.3 at 823 K and a high average ZT of ∼0.8 for Sb1.99Ca0.01Si2Te6, showing its potential for power generator at medium temperature.