Stability and fundamental properties of CuxO1−x as optoelectronic functional materials

Abstract

Binary Cu_xO_1−x compounds have some advantages as optoelectronic functional materials, but their further development has encountered some bottlenecks, such as inaccurate bandgap values and slow improvement of photoelectric conversion efficiency. In this work, all possible stoichiometric ratios and crystal structures of binary Cu_xO_1−x compounds were comprehensively analyzed based on a high-throughput computing database. Stable and metastable phases with different stoichiometric ratios were obtained. Their stability in different chemical environments was further analyzed according to the component phase diagram and chemical potential phase diagram. The calculation results show that Cu, Cu₂O and CuO have obvious advantages in thermodynamics. The comparison and analysis of crystal microstructure show that the stable phase of Cu_xO_1−x compounds contains the following two motifs: planar square with Cu atoms as the center and four O atoms as the vertices; regular tetrahedron with O atoms as the center and four Cu atoms as the vertices. In different stoichiometric ratio regions, the electron transfer and interaction modes between Cu and O atoms are different. This effect causes energy differences between bonding and antibonding states, resulting in the different conductivity of binary Cu_xO_1−x compounds: semi-metallic ferromagnetic, semiconducting, and metallicity. This is the root of the inconsistent and inaccurate bandgap values of Cu_xO_1−x compounds. These compositional, structural, and property variations provide greater freedom and scope for the development of binary Cu_xO_1−x compounds as optoelectronic functional materials.