Bandgap engineering via tuning of S and Se content in Cu2ZnSn(S, Se)4 for improved thermoelectric properties

Abstract

Thermoelectric materials are in high demand for sustainable energy solutions since they are essential for turning waste heat into usable electrical energy or solid-state refrigeration. Chalcogenides have emerged as promising materials in the field of thermoelectrics, which typically consist of three elements, often including a chalcogen (sulfur, selenium, or tellurium) combined with transition metals or other elements. The unique crystal structure and electronic properties of ternary chalcogenides contribute to their excellent thermoelectric performance. They possess high thermoelectric efficiency due to their ability to simultaneously exhibit low thermal conductivity and high electrical conductivity. In this study quaternary chalcogenides Cu2ZnSn (Sx, Se1-x)4 compounds were synthesized successfully by adopting the mechanochemical alloying (ball milling) method. The synthesis process consists of three main steps: ball milling of elemental precursors, sintering and densification through cold isostatic pressing (CIP). We hereby report the structural characterization and thermoelectric investigations carried out on samples milled at 200 rpm for 3hrs followed by sintering at 500°C. X-ray diffraction (XRD) and EDX were carried out for phase and composition analysis. Thermoelectric properties, such as electrical conductivity ( ), thermal conductivity ( ), and Seebeck coefficient (S), were measured over a temperature range of 300–600 K. The maximum thermoelectric figure of merit (ZT) obtained is for Cu2ZnSnS2.8Se1.2.with a value of 0.12 at 600K. These values closely resemble the reported figure of merit for compounds synthesized using solid-state techniques.