Synergistic optimization of electronic structure and defects via light Zn-doping for high performance n-type Bi₂(Te, Se)₃ thermoelectrics in cooling and power generation

The interdependence of electrical parameters has long inhibited the progress of bismuth telluride (Bi₂Te₃), limiting its widespread application in thermoelectric cooling and power generation. This work investigates the n-type Bi₂Te_2.79Se_0.21I_0.004 (BTS) system with light Zn doping, revealing that Zn addition simultaneously enhances the Seebeck coefficient (S) and electrical conductivity (σ) through the modulation of defect composition and multi-level band regulation. The substitution of Zn atoms at Bi sites enhances S via bandgap (E_g) widening, band flattening and splitting effects, contributing to a competitive power factor (PF) to ~60 μW cm^-1 K^-2. Additionally, thermal conductivity is maintained at a low level, leading to an extraordinary figure-of-merit ZT value of ~1.3 at room temperature. Furthermore, the Bi₂Zn_0.01Te_2.79Se_0.21I_0.004 system demonstrates impressive thermoelectric device performance, with a maximum room-temperature cooling difference (ΔT_max) of ~70.0 K and rising to ~78.0 K at 323 K and ~85.7 K at 343 K, as well as a maximum conversion efficiency (η_max) of ~6.2% under a ΔT of 200 K. This study clarifies the mechanism of Zn doping and presents a cost-effective strategy for enhancing the performance of n-type BTS thermoelectrics and devices.