CsCu5Se3: A Copper-Rich Ternary Chalcogenide Semiconductor with Nearly Direct Band Gap for Photovoltaic Application

Discovery of new semiconductor candidates with suitable band gaps is a challenge for optoelectronic application. A facile solvothermal synthesis of a new ternary chalcogenide semiconductor CsCu₅Se₃ is reported. The telluride CsCu₅Te₃ is also predicted to be stable. CsCu₅Se₃ is isostructural with CsCu₅S₃ (space group Pmma). The band gap calculations of these chalcogenide semiconductors using hybrid density functional theory indicate nearly direct band gaps, and their values (about 1.4 eV) were confirmed by the optical absorption spectroscopy. These alkali metal copper chalcogenides are interesting examples of copper-rich structures which are commonly associated with favorable photovoltaic application.