Strengthened interlayer interaction and improved room-temperature thermoelectric performance of Ag-doped n-type Bi2Te2.7Se0.3

Doping n-type Bi2Te3-based alloys with Cu or Ag has been proven an effective way to improve their thermoelectric performance. However, the doping behavior is still not clear and the underneath mechanism needs more evidence to clarify. Herein, a study on the structure and transport properties of polycrystalline Ag-doped n-type Bi2Te2.7Se0.3 is performed. Raman and X-ray photoelectron spectroscopy analysis suggests that Ag ions are situated at the interstitial sites and transfer electrons to the neighbouring Te(Se). The newly established Ag-Te(Se) bonds lead to strengthened interlayer interaction and improved carrier mobility. Te(Se) vacancy, as an intrinsic feature in the polycrystalline Bi2Te2.7Se0.3 alloy, is alleviated due to the formation of Ag-Te(Se) bonds. The carrier concentration can be gradually adjusted to a lower level, at which largely improved room-temperature thermoelectric performance is yielded. As a result, the room-temperature dimensionless figure of merit ZT value and cooling performance of the optimal Ag-doped Bi2Te2.7Se0.3 are enhanced by nearly 60% and 75% as compared with those of the pristine Bi2Te2.7Se0.3.