Hybridization of n-type Bi₂Te₃ crystals with liquid-like copper chalcogenide elicits record-high thermoelectric performance

The modern era of thermoelectricity (TE) is born alongside the explosion of nanotechnology. Although high-dose doping rejuvenates TE research, expectations for low thermal conductivity κ and high electrical transport property remain conflicting. The n-type Bi₂Te₃ with dilute liquid-like copper chalcogenide realizes the hybridization of electronic and ionic conduction and fulfills the concept of phonon-liquid electron-crystal. The presence of Cu₂S nano-clusters modulates the concentration of Cu and Cu ion dynamically. Under such circumstances, the solubility of Cu in n-type Bi₂Te₃ retains at a maximal level without forming undesired impurity phases. Moreover, the Cu ions play a double role as phonon scatters and high-mobility carriers, yielding the reduced κ_L with enhanced carrier mobility μ_H. Meanwhile, a high electrical conductivity σ is retained by pinning the carrier concentration n_H in the optimal level of 10¹⁹ cm⁻³ with the incorporation of electron donors. Consequently, our nearly single-phase n-type Bi₂Se_0.02Te₃Cu_0.03(Cu₂S)_0.0125 crystal achieves a large S²σ, a record-breaking zT = 1.6 at 363 K, and an ultrahigh average zT = 1.38 in the temperature range of 300 K–500 K.