Enhanced Solubility of Ga and Deep Defect Level Lead to High Thermoelectric Performance of n-Type Pb1–xGaxTe0.995I0.005 Alloys

By virtue of temperature differences, which are in hundreds of kelvin, the optimized carrier concentration may vary within an order of magnitude. Ga has shown potential in providing temperature-dependent carrier concentration due to its deep level of impurity states, which can ionize and release electrons at higher temperature. However, because of the low solubility, the decreasing of lattice thermal conductivity in the Ga-doped PbTe system is constrained. In this study, monovalent I is introduced, which leads to the solubility of Ga in PbTe reaching 5% and tunes the carrier concentration in PbTe simultaneously. An enhanced maximum PF of 21 μW K–2 cm–1 and ultralow lattice thermal conductivity of 0.61 W m–1 K–1 are attained because of the incorporation of Ga, which together enable an enhanced peak zT of 1.2, an average value of zT to 0.61, and a thermoelectric conversion efficiency η of 9.3% for the Pb0.95Ga0.05Te0.995I0.005 sample.