Structural, electronic, optical, and photovoltaic properties of 4-atom Au-Ag-Cu clusters: a first-principles study

The structural, electronic, optical, and photovoltaic properties of 4-atom Au-Ag-Cu clusters were systematically investigated using GGA/PBE. The Au₃Ag₁, Au₃Cu₁, Ag₃Cu₁, Cu₃Au₁, Ag₁Cu₃, and Ag₂Cu₁Au₁ clusters are found to adopt three-dimensional trigonal pyramidal configurations. The structures of pure clusters and Au₁Ag₃, Au₂Ag₂, Au₂Cu₂, Ag₂Cu₂, Ag₁Cu₂Au₁, and Ag₁Cu₁Au₂ clusters are found to exhibit two-dimensional planar structures. Among these clusters, Au₂Cu₂ and Ag₁Cu₁Au₂ are identified as more stable than their neighboring clusters, and high alloying degrees are observed in Ag₂Cu₂, Au₃Cu₁, Au₂Cu₂, Au₂Ag₂, and the ternary clusters. Ag₂Au₂ and Au₂Cu₂ clusters possess the largest energy gaps. The energy gaps of Ag₁Cu₁Au₂, Ag₁Cu₂Au₁, and Ag₂Cu₁Au₁ clusters are larger than those of pure clusters, indicating their superior electronic stability. Doping Cu and Au clusters with Ag atoms is favorable for enhancing the absorption intensity in the visible and near-ultraviolet regions. Compared with binary clusters containing the same number of Ag atoms, ternary clusters display stronger absorption peak intensities in the visible and near-ultraviolet regions. Furthermore, clusters with higher Ag content exhibit better light absorption ability, lower recombination energy, and shorter excited-state lifetimes. The light-harvesting capability and optoelectronic properties of 4-atom Au-Ag-Cu clusters are studied. Strong absorption in the near-ultraviolet and visible regions is observed. These results confirm the promising potential of these clusters as optoelectronic materials and provide a feasible strategy for designing novel photosensitizers for dye-sensitized solar cells.