The effects of Ag⁺ and Al³⁺ substitution in (Cu_1-xAg_x)(In_1-x Al_x)S₂ chalcopyrite nanoparticles synthesized by hydrothermal method: Study of microstructures and optical properties

In this research, Ag⁺ and Al³⁺ doped CuInS₂ (CIS) nanoparticles were synthesized by a low-cost and non-vacuum hydrothermal method. The CuInS₂ nanoparticles were synthesized by the stoichiometric ratio of (1Cu: 1In: 2S) using the hydrothermal method at 180℃ and for 16, 18 and 20 h. Afterward, Ag⁺ and Al³⁺ ions were doped with non-stoichiometric composition of (Cu_1-xAg_x)InS₂, Cu(In_1-xAl_x)S₂ (x = 0.1, 0.2, and 0.3), and (Cu_1-xAg_x)(In_1-xAl_x)S₂ (x = 0.1). The phase evolution, microstructural, and optical properties have also been studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), UV–Vis spectroscopy techniques. The XRD results showed that the sample was prepared by the hydrothermal route at 180° C for 20 h was single-phase and no impurity phase was detected. However, some minor impurity phases (CuS and Cu₉S₅) were detected in the samples were synthesized at 180° C in 16 h and 18 h. The results show that the crystallite size of the synthesized nanoparticles of CIS at 16, 18, and 20 h are 26, 29, and 32 nm, respectively. The lattice parameters for the sample synthesized in 20 h were calculated to be 5.52 Å (a) and 11.11 Å (c). The FE-SEM micrographs showed that the pure CIS nanoparticles have flower-shaped morphology and the type and concentration of used dopants affect the morphology of the nanoparticles. The bandgap of single-phase CIS synthesized nanoparticles was 1.5 eV. However, the bandgap of (Cu_0.9Ag_0.1)InS₂ and Cu(In_0.9Al_0.1)S₂ was 1.4 eV and 1.70, respectively. The bandgap of (Cu_0.9Ag_0.1) (In_0.9Al_0.1)S₂ was 2 eV.