Center for Informatics researchers show how the stability of 2D perovskites is enhanced compared to bulk | Shiv Nadar University
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Center for Informatics researchers show how the stability of 2D perovskites is enhanced compared to bulk

Research
23 Sep 2019
  • Representation of hybrid halide perovskites in bulk (MASnBr3) and in layerered structures (R2SnBr4)

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

Dr. Anu Bala and Prof. Vijay Kumar, in a paper just published in the Journal of Physical Chemistry C (2019) have shown how the stability of 2D structures of perovskites is enhanced compared to bulk. The inorganic part of these Organic-inorganic metal halide perovskites is the main contributor to the electronic and optical properties of the layers, while the van der Walls interactions between the ligands play a central role in enhancing the stability of the layers. These 2D systems constitute currently an important direction of research for solar energy materials.

Authors: Anu Bala and Vijay Kumar

Journal of Physical Chemistry C (2019) https://doi.org/10.1021/acs.jpcc.9b06395

Organic-inorganic metal halide perovskites have attracted a great deal of interest because of their promising applications in solar cells and high-performance optoelectronic devices. Recently, two-dimensional (2D) layered perovskites have become the focus of much attention due to their better stability. Although much experimental work has been done on metal halide perovskite layers, there is a need to understand the phenomenon responsible for their improved stability. This is more so because our earlier theoretical studies [J. Phys. Chem. C 122, 7464 (2018)] showed lower stability of layers without ligands compared with bulk. In the present paper, we report results of the state-of-the-art ab initio calculations on two-dimensional (2D) hybrid halide perovskites: R2SnBr4, capped with surface ligands ((R=methyl ammonium: MA, ethyl ammonium: EA, butyl ammonium: BA, and phenylethyl ammonium: PEA) to understand their effects on the stability with respect to bulk MASnBr3 (MA = CH3NH3). Our calculations show 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.
  • 2D-3D BA2SnBr4 system in which the surface ligands connect the neighboring perovskite layers (as shown in figure), suggest further enhancement in the stability of the layers.
  • The interactions between the head of the organic ligand and bromine atoms of the octahedra affects the structure of the inorganic layers.
  • All the studied perovskite layers are direct band gap semiconductors and the environment friendly BA2SnBr4 (PEA2SnBr4) layers are good candidates for green LEDs with a band gap of ~2.28 (2.36) eV.
  • The band gap of layers increases slightly on increasing the length of the ligands and there is a slight blue shift of the absorption spectrum.

In a nutshell, the inorganic part of these Organic-inorganic metal halide perovskites is the main contributor to the electronic and optical properties of the layers, while the van der Walls interactions between the ligands play a central role in enhancing the stability of the layers.

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