Exploring the optical characteristics influenced by size and surface defects in AgInS2 quantum dots: A theoretical study with a simple ligand model

Despite the recent great interest in ternary AgInS₂ quantum dots (QDs), theoretical studies on fundamental features such as size-dependent optical properties and surface defect characteristics have been relatively scarce. This is due to the practical difficulty of performing electronic structure calculations that take into account not only the structural complexity of ternary AgInS₂ QDs compared to conventional binary QDs, but also the complex organic ligands that cover the inorganic crystalline surface. In this study, we theoretically explored the optical properties of AgInS₂ QDs from the cluster structures by introducing a simple ligand model that mimics the role of real ligands for surface passivation. First, an analytical equation is presented that relates size and bandgap, which indicates that the quantum confinement effect of AgInS₂ QDs is smaller than that of binary InP QDs. Through electronic structure calculations of surface defects, it was found that surface In defects alone or in combination with surface S defects significantly inhibit radiative transition properties, whereas surface Ag defects do not adversely affect its optical properties. Furthermore, synthesis and measurement of AgInS₂ QDs validate the bandgap equation and surface defect characteristics.