Lead-free 2D MASnBr₃ and Ruddlesden-Popper BA₂MASn₂Br₇ as light harvesting materials

We have explored the structural, electronic, charge transport, and optical properties of lead-free 2D hybrid halide perovskites, MASnBr₃ and Ruddlesden-Popper perovskites, BAMASn₂Br₇ monolayers. Under density functional theory (DFT) calculation, we applied mechanical strain, i.e., tensile and compressive strain up to 10% in both cases. The mechanical strain engineering technique is useful for a tuned bandgap of 2D MASnBr₃ and 2D BAMASn₂Br₇. The calculated carrier mobility for the electron is 404 cm² V^-1 s^-1 and for the hole is up to 800 cm² V^-1 s^-1 for MASnBr₃. For BAMASn₂Br₇ the highest carrier mobility is up to 557 cm² V^-1 s^-1 for electrons and up to 779 cm² V^-1 s^-1 for the hole, which is 14% and 24% higher than the reported lead-iodide based perovskites, respectively. The calculated solar cell efficiency of 2D MASnBr₃ is 23.46%, which is 18% higher than the reported lead-based perovskites. Furthermore, the optical activity of the 2D MASnBr₃ and 2D BAMASn₂Br₇ shows a high static dielectric constant of 2.48 and 2.14, respectively. This is useful to show nanodevice performance. Also, 2D MASNBr₃ shows a high absorption coefficient of 15.25 × 10⁵ cm^-1 and 2D BAMASn₂Br₇ shows an absorption coefficient of up to 13.38 × 10⁵ cm^-1. Therefore our theoretical results suggest that the systems are under mechanical strain engineering. This is convenient for experimentalists to improve the performance of the 2D perovskites. The study supports these materials as good candidates for photovoltaic and optoelectronic device applications.