Tailoring the thermoelectric performance of 3D-printed n-type Bi2Te2.7Se0.3 through Ag doping in vdW-gaps

Thermal-driven Ag intercalation enables vdW-gaps doping in 3D-printed n-type Bi 2 Te 2.7 Se 0.3 . • vdW-gaps Ag enhances electrical transport and lowers lattice thermal conductivity. • Peak ZT of 1.26 and module efficiency of 6.0% are achieved. Bi 2 Te 3 -based materials are recognized as the benchmark thermoelectrics for near-room-temperature applications. However, substantially inferior thermoelectric performance in n-type Bi 2 Te 3 compared to highly performance p-type variants creates a critical performance asymmetry, restricting energy conversion efficiency. Herein, we develop thermal-driven Ag intercalation into van der Waals (vdW) gaps of 3D-printed n-type Bi 2 Te 2.7 Se 0.3 (BTS), achieving vdW-gaps doping. The first-principles calculations demonstrate that interstitial Ag atoms are mainly located at the vdW gaps, which reduces their direct perturbation to the conductive layers. As a result, they provide spatially separated conduction electrons, increasing carrier concentration while sustaining high carrier mobility. Furthermore, the Ag-intercalation-induced superlattice structures efficiently scatter mid-to-long wavelength phonons, thereby effectively suppressing lattice thermal conductivity. Ultimately, the BTS + 0.2% Ag intercalated sample achieves a peak ZT of 1.26 at 375 K, with an average ZT ∼1.12 maintained across the operational temperature range of 300-500 K. Leveraging such exceptional thermoelectric performance, a thermoelectric module assembled with 127 pairs legs delivers a conversion efficiency of 6.0% under ΔT = 180 K. This work provides a facile thermal-driven Ag intercalation strategy for vdW-gaps doping of n-type Bi 2 Te 3 -based thermoelectrics, breaking the performance asymmetry bottleneck and enabling high-efficiency near-room-temperature thermoelectric modules.