An investigation on physical properties of Ag₂BiI₅ absorber layers synthesized by microwave assisted spin coating technique

Silver bismuth iodide perovskites are good substitutes instead of lead-based perovskites because they are nontoxic and stable in air. In this study, Ag–Bi–I thin films with various ratios of Ag/Bi = 3, 2, 1, 0.5 were prepared by spin coating of AgI and BiI₃ dissolved in dimethylsulfoxide. In this research, Microwave was used for heat treatment of perovskite films in the air. The morphology, structure, stability and composition of the studied layers have been studied by X-ray diffraction (XRD), energy-dispersive X-ray analysis, and field emission scanning electron microscope (FESEM). Also, the correlation between the optical data, and the silver concentration of thin films was established. Structural characterizations showed the hexagonal phase of Ag₂BiI₅ for all samples. The magnified FESEM images show that after heat treatment by microwave, all films had a dense surface with the spherical structures and the average diameter smaller than 50 nm. Also these samples had various band gap energies between 1.38 and 1.6 eV After heat treatment in air and after 30 days in ambient condition under relative humidity of 50%, XRD patterns and band gap energies was not changed so these samples showed excellent long-time stability. These two characteristics make these materials especially suited for solar cells.