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.