Engineering the p-n switch: Mastering intrinsic point defects in Sb2Te3-dominant alloys

Abstract

V2VI3-based alloys have long been established as the sole commercial material system for solid-state cooling. However, the volatility of the Se element in conventional n-type Bi2Te3-xSex leads to inconsistent reproducibility across production batches. Here, we unveil an innovative, highly reproducible n-type Bi0.5Sb1.5Te3 alloy, realized through strategic manipulation of native point defect. The initial Bi0.5Sb1.5Te3 is saturated with antisite defects, imbuing it with pronounced p-type conductivity. Our investigation, underpinned by the electronegativity and atomic size model and validated through density functional theory calculation, reveals that the replacement of Sb by In in the Bi0.5Sb1.5-xInxTe3 system effectively elevates the formation energy of negatively charged antisite defect, while simultaneously diminishing that of positively charged anion vacancy. This alteration in the dominant point defect type catalyzes a p-n type transition, prominently observed at around x = 0.15. We believe this constitutes the inaugural disclosure of a n-type Sb2Te3-rich bulk material. The observed low zT ∼ 0.16 at 360 K in n-type Bi0.5Sb1.05In0.45Te3, attributed to low electron mobility, is a focal point for ongoing performance enhancement efforts. These results not only enrich the comprehension of intrinsic point defect manipulation in the V2VI3 system, but also pave the way for the systematic evolution and realization of innovative, high-efficiency, and consistently reproducible n-type Bi2-xSbxTe3 alloys.