Achieving ultrahigh power factor in n-type Ag2Se thin films by carrier engineering

Abstract

Ag2Se-based thermoelectric materials are attracting great attention because of their potential in fabricating high-performance miniature and wearable electronics. Here, an advanced thermal co-evaporation method is employed to fabricate high-performance Ag2Se thin films with controllable compositions. The atomic ratio Ag/Se of 2.06 can tune the carrier concentration to 1.4 × 1019 cm−3, leading to a power factor of 6.27 μW cm−1K2 at room temperature. As well, an annealing process further improves the electrical transport properties by increasing the carrier mobility while maintaining the carrier concentration. Microstructure analysis indicates that annealing can reduce dislocation defect density and Ag vacancy concentration, contributing to a high Seebeck coefficient, finally resulting in a high power factor of 20.51 μWcm−1K−2 at 393 K. Moreover, a thermoelectric device composed of 18 legs is fabricated by using the optimized Ag2Se thin film, which presents a maximum output voltage and power of ∼1.7 mV and ∼22 nW at the temperature difference of 50 K. These results demonstrate that a combination of compositional optimization and annealing condition manipulation is effective to boost the thermoelectric performance of Ag2Se thin films, showing great potentials in applying for wearable electronics.