Grape juice: an effective liquid additive for significant enhancement of thermoelectric performance of Cu2Se

Abstract

The reduction of thermal conductivity and enhancement of electrical properties is the ultimate goal for achieving high-performance thermoelectric materials. In this paper, a high thermoelectric performance is demonstrated when grape juice is used as an additive to Cu₂Se. High temperature processing of the mixture pyrolyzes the sugars in the grape juice and provides a fine-scale and well-mixed dispersion of elemental carbon in the Cu₂Se matrix. These materials show a significant enhancement of electrical conductivity due to a high hole concentration with little change of the Seebeck coefficient, leading to an ultra-high power factor of 1.3 mW m⁻¹ K⁻² at 984 K. Microstructural studies reveal that the carbon phase is embedded on the Cu₂Se grain boundaries and that Cu₂O nanoparticles are located at the interface between carbon and Cu₂Se. This results in phonon scattering at the interface which leads to a reduction of thermal conductivity of up to ∼38%. It is proposed that the formation of Cu₂O also induces Cu deficiencies in Cu₂Se resulting in greater enhancement of electrical conductivity. As a result, the zT is significantly enhanced up to ∼2.5 at 984 K. This study opens up a new avenue for enhancing the properties of thermoelectric materials.