Ultrahigh power factor in thermally evaporated Bi/Ag2Se bi-layer obtained using thermal inter-diffusion

Abstract

Bi/Ag2Se bi-layer (ASB) has been deposited using simple thermal evaporation. Both the layers are interdiffused thermally at transition temperatures of 130 (ASB-130) and at 210 °C (ASB-210) for a soaking time of 1 h each. ASB-210 shows a promising in-plane thermoelectric power factor of 1.4 mW/m K2 at 30 °C and 1.5 mW/m K2 at 90 °C. This ultrahigh value in ASB-210 is due to simultaneous improvement in carrier concentration and mobility values (enhances σ). Moreover, (013) grain orientation and uniform distribution of Ag and Bi in Ag2Se matrix are inferred to be other reasons for power factor improvement. The power factor of ASB-210 is found to be nearly stable in the temperature range of 30–90 °C. This constant value is accredited to suppression of bipolar effect in Ag2Se by Ag and Bi nano-inclusions. Ag, Bi impurities are held responsible for carrier scattering. Moreover, formation of Ag/Ag2Se and Bi/Ag2Se heterostructures promotes hot carrier filtering, which enhances the Seebeck coefficient. Thus, decoupling of electrical conductivity and Seebeck coefficient is achieved. This technique of enhancing thermoelectric performance has not been reported for Ag2Se films.