Role of Ligand–Ligand Interactions in the Stabilization of Thin Layers of Tin Bromide Perovskite: An Ab Initio Study of the Atomic and Electronic Structure, and Optical Properties

Abstract

We report results of the state-of-the-art ab initio calculations on two-dimensional (2D) hybrid halide perovskites capped with surface ligands to understand their effects on the stability with respect to bulk MASnBr3 (MA = CH3NH3). Considering the thinnest (one-unit-cell thick) layers R2SnBr4 with surface ligands of different lengths (R = MA, ethyl ammonium (EA), butyl ammonium (BA), and phenylethyl ammonium (PEA)), it is found that van der Waals (vdW) interactions between the long chain molecules play a crucial role in enhancing the stability of the layers. The vdW contribution in ligand–ligand interactions increases with increasing length of the ligands, and interestingly, the stability of BA2SnBr4 and PEA2SnBr4 layers becomes better than bulk MASnBr3 and comparable to that of inorganic bulk CsSnBr3. Furthermore, our calculations on the 2D-3D BA2SnBr4 system in which the surface ligands connect the neighboring perovskite layers suggest further enhancement in the stability of the layers. The present study shines light on the role of H···Br bonding in deciding the structure of the inorganic part of these thinnest layers and the effect of inclusion of vdW interactions on these H···Br bond lengths. The band gap of the layers increases slightly on increasing the length of the ligands, and there is a slight blue shift of the absorption spectrum. All the studied perovskite layers are direct band gap semiconductors, and our results show that the environmentally friendly BA2SnBr4 (PEA2SnBr4) layers are good candidates for green LEDs with a band gap of ∼2.28 (2.36) eV as obtained by using the HSE06 hybrid exchange-correlation functional with dispersion correction.

Effects of Cl and F Substitution in Phenylethylammonium Spacer Cations on Stability, Structure, and Optical Properties of 2D–3D Ruddlesden–Popper Perovskite Layers

“…Recently, we have shown that the optical properties of organic−inorganic hybrid halide perovskites primarily depend on the inorganic framework 43 and any change in the optical behavior can be attributed to an increase in the in-plane octahedral distortions. 30,44 Therefore, in order to explore the effect of chemical tuning of spacer cations on the inorganic framework, we have shown the principal interactions between the organic cations and the inorganic framework through H1••• I5, H1•••I6, H3•••I7, and H2•••I8 bonds, as marked in Figure 6, and the values have been tabulated in Table 2.…”

“…Recently, we have shown that the optical properties of organic–inorganic hybrid halide perovskites primarily depend on the inorganic framework and any change in the optical behavior can be attributed to an increase in the in-plane octahedral distortions. , Therefore, in order to explore the effect of chemical tuning of spacer cations on the inorganic framework, we have shown the principal interactions between the organic cations and the inorganic framework through H1···I5, H1···I6, H3···I7, and H2···I8 bonds, as marked in Figure , and the values have been tabulated in Table . These interactions may distort the PbI 6 octahedra in layers, and this distortion can be measured in terms of various octahedra angles (∠ Pb 1 I 2 Pb 2, ∠ Pb 1 I 3 Pb 3, ∠ Pb 1 I 4 Pb 4, and ∠ Pb 1 I 5 Pb 5) and Pb–I bond lengths (Figure and Table ).…”

Water‐Stable DMASnBr3 Lead‐Free Perovskite for Effective Solar‐Driven Photocatalysis

“…Some of us also recently reported an extremely high stability of two‐dimensional (2D) lead‐free perovskites based on phenylethylammonium (PEA), namely PEA 2 SnBr 4 , which, as well, does not dissolve in water (but disperse) and which structural and optical properties remain unchanged after water treatments [14] . For 2D perovskites some computational work is addressing such improved water stability, showing also that the same mechanism is thought to protect tin from +2 to +4 oxidation [15] . Finally, very recently, a novel 1D hybrid tin iodide material, namely (DAO)Sn 2 I 6 (DAO, 1,8‐octyldiammonium), has shown to emit broad light with high quantum efficiency and stability in water for more than 15 hours [16] …”

Interfacial engineering in lead-free tin-based perovskite solar cells

“…The results indicate that FASnI 3 can be transformed into intrinsic semiconductor by regulating its conductivity under precisely controlled growth condition. However, the fact is different for MASnI , on the stability of Sn-based perovskites [77]. The DFT calculations on the 2D-3D system suggest further stability enhancement of the neighboring layers with connection of surface ligands by forming a passivated 3D surface (Fig.…”