The Role of Connectivity on Electronic Properties of Lead Iodide Perovskite-Derived Compounds

Abstract

We use a layered solution crystal growth method to synthesize high-quality single crystals of two different benzylammonium lead iodide perovskite-like organic/inorganic hybrids. The well-known (C6H5CH2NH3)2PbI4 phase is obtained in the form of bright orange platelets, with a structure comprised of single ⟨100⟩-terminated sheets of corner-sharing PbI6 octahedra separated by bilayers of the organic cations. The presence of water during synthesis leads to formation of a novel minority phase that crystallizes in the form of nearly transparent, light yellow bar-shaped crystals. This phase adopts the monoclinic space group P21/n and incorporates water molecules, with structural formula (C6H5CH2NH3)4Pb5I14·2H2O. The crystal structure consists of ribbons of edge-sharing PbI6 octahedra separated by the organic cations. Density functional theory calculations including spin–orbit coupling show that these edge-sharing PbI6 octahedra cause the band gap to increase with respect to corner-sharing PbI6 octahedra in (C6H5CH2NH3)2PbI4. To gain systematic insight, we model the effect of the connectivity of PbI6 octahedra on the band gap in idealized lead iodide perovskite-derived compounds. We find that increasing the connectivity from corner-, via edge-, to face-sharing causes a significant increase in the band gap. This provides a new mechanism to tailor the optical properties in organic/inorganic hybrid compounds.

White light emission in low-dimensional perovskites

“…The band structure, emissive properties and defect formation energy of perovskites are significantly affected by the connectivity of the inorganic motif. 25 The perovskite structural properties can be evaluated using some relevant parameters:…”

“…The connectivity gradually increases from corner to edge and face-sharing octahedra, which results in band-gap widening and can modulate the confinement effects in the low dimensional structures. 19,25,38…”

Excitons in 2D Organic–Inorganic Halide Perovskites

“…Although the inorganic lattice is most commonly formed as a (100)-oriented flat sheet of corner-sharing [PbX 6 ] 2-octahedra, 13 their connectivity can vary, leading to more exotic structures such as the (110) zig-zag 25 or corrugated structures 26 (Figure 2c) and edgeand face-sharing octahedra networks (Figure 3a). 27 The organic layer determines other properties of the hybrid 2DLP as well, such as its hydrophobicity and stability; 21,[28][29] structural rigidity; 20,30 sheetto-sheet distance; [31][32][33] and the dielectric screening experienced by charge carriers confined within the inorganic layer. [34][35][36] Early work focused primarily on n = 1 layered perovskites, in which the alternating stacks of organic cations surround atomically-thin inorganic sheets.…”

Thermal stability of mobility in methylammonium lead iodide

“…Because the technique does not require electrical contacts or transport layers, it can be carried out on isolated thin films, discontinuous films or even powders. The absence of physical contacts removes contributions from external interfaces [29,33,34], and enables us to make unambiguous statements on the thermal stability of the compound itself. For MHPs such as MAPbI 3 the exciton binding energy is known to be very small [35], and we can approximate f » 1.…”