Prefer-Oriented Ag₂Se Crystal for High-Performance Thermoelectric Cooling

Ag₂Se-based materials with promising room-temperature thermoelectric performance have been known for decades. However, thermoelectric cooling devices based on bulk Ag₂Se have seldom been reported, mainly due to the phase transition ≈400 K poses a grand challenge for leg design and module integration. Herein, Ag₂Se crystals with the preferred orientation have been prepared. A high carrier mobility of ≈1846 cm² V⁻¹ s⁻¹ and a power factor of ≈31.2 µW cm⁻¹ K⁻² at room temperature has been realized, and results in a zT of ≈0.95 at 300 K. Importantly, by applying Ag as the contact layer, the Ag/Ag₂Se/Ag joint has been prepared by one-step sintering. By maintaining the pressure of ≈10 MPa after sintering and during the reflow soldering, the deleterious effect of the large thermal expansion can be alleviated. The contact resistance of the Ag/Ag₂Se interface is as low as ≈2.9 µΩ cm², indicating negligible electrical parasitic loss. The thermoelectric device with 7 pairs of Ag₂Se and (Bi, Sb)₂Te₃ has been fabricated and it can achieve a maximum cooling power of ≈2.90 W and a cooling temperature difference of ≈70.4 K at the hot-side temperature of 350 K, demonstrating the great potential of Ag₂Se for cooling applications.