Chemical and Structural Diversity of Hybrid Layered Double Perovskite Halides

Hybrid halide double perovskites are a class of compounds attracting growing interest because of their richness of structure and property. Two-dimensional (2D) derivatives of hybrid double perovskites are formed by the incorporation of organic spacer cations into three-dimensional (3D) double perovskites. Here, we report a series of seven new layered double perovskite halides with propylammonium (PA), octylammonium (OCA), and 1,4-butyldiammonium (BDA) cations. The general formulas of the compounds are AM^IM^IIIX₈ (single-layered Ruddlesden-Popper type with m = 4 and A = PA or OCA, and single-layered Dion-Jacobson type with m = 2 and A = BDA, M^I = Ag, M^III= In or Bi, X = Cl or Br) and PA₂CsM^IM^IIIBr₇ (bilayered, with M^I = Ag, M^III = In or Bi). These families of compounds demonstrate great versatility, with tunable layer thickness, the ability to vary the interlayer spacing, and the ability to selectively tune the band gap by varying the M^I and M^III cations along with the halide anions. The band gap of the single-layered materials varies from 2.41 eV for PA₄AgBiBr₈ to 3.96 eV for PA₄AgInCl₈. Photoluminescent emission spectra of the layered double perovskites at low-temperature (100 K) are reported, and density functional theory electronic structure calculations are presented to understand the nature of the band gap evolution. The development of new structural and compositions in layered double perovskite halides enhances the understanding of structure-property relations in this important family.