The effect of cations in electronic, and optical properties of lead-free halide perovskites based on Sn–Ge

In this work, the electronic and optical properties of three-dimensional (3D) lead-free hybrid perovskites [Formula: see text][Formula: see text] with organic and inorganic cations [Formula: see text], Cs ([Formula: see text]) have been investigated using density functional theory (DFT). The nature of the cations in the 3D perovskite structure has a significant impact on the electronic and optical properties of the 3D structures because octahedral [Formula: see text] is so sensitive to them. The results revealed that by replacing the organic cation with the inorganic cation, the band gap has increased, and also in the optical properties, an increase in the absorption coefficient and a decrease in reflection have been observed. According to the obtained results, the [Formula: see text] compound is a better candidate for optoelectronic devices and solar cells applications than [Formula: see text], due to its higher band gap, higher absorption coefficient, lower reflection, and cheaper price. These findings are crucial for comprehending how cations affect lead-free perovskite halides, and we hope it will be a useful guide for improving the photovoltaic efficiency of lead-free perovskite solar cells. In addition to the absorber layer of solar cells, 3D perovskites are used in laser and thermoelectric applications, topological insulation, and radiation detection.