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

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 (C 6 H 5 CH 2 NH 3 ) 2 PbI 4 phase is obtained in the form of bright orange platelets, with a structure comprised of single ⟨100⟩-terminated sheets of corner-sharing PbI 6 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 P2 1 /n and incorporates water molecules, with structural formula (C 6 H 5 CH 2 NH 3 ) 4 Pb 5 I 14 ·2H 2 O. The crystal structure consists of ribbons of edge-sharing PbI 6 octahedra separated by the organic cations. Density functional theory calculations including spin-orbit coupling show that these edge-sharing PbI 6 octahedra cause the band gap to increase with respect to corner-sharing PbI 6 octahedra in (C 6 H 5 CH 2 NH 3 ) 2 PbI 4 . To gain systematic insight, we model the effect of the connectivity of PbI 6 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.