Silver‐Bismuth Based 2D Double Perovskites (4FPEA)₄AgBiX₈ (X = Cl, Br, I): Highly Oriented Thin Films with Large Domain Sizes and Ultrafast Charge‐Carrier Localization

Abstract

Two‐dimensional (2D) hybrid double perovskites are a promising emerging class of materials featuring superior intrinsic and extrinsic stability over their 3D parent structures, while enabling additional structural diversity and tunability. Here, we expand the Ag–Bi‐based double perovskite system, comparing structures obtained with the halides chloride, bromide, and iodide and the organic spacer cation 4‐fluorophenethylammonium (4FPEA) to form the n = 1 Ruddlesden–Popper (RP) phases (4FPEA)4AgBiX8 (X = Cl, Br, I). We demonstrate access to the iodide RP‐phase through a simple organic spacer, analyze the different properties as a result of halide substitution and incorporate the materials into photodetectors. Highly oriented thin films with very large domain sizes are fabricated and investigated with grazing incidence wide angle X‐ray scattering, revealing a strong dependence of morphology on substrate choice and synthesis parameters. First‐principles calculations confirm a direct band gap and show type Ib and IIb band alignment between organic and inorganic quantum wells. Optical characterization, temperature‐dependent photoluminescence, and optical‐pump terahertz‐probe spectroscopy give insights into the absorption and emissive behavior of the materials as well as their charge‐carrier dynamics. Overall, we further elucidate the possible reasons for the electronic and emissive properties of these intriguing materials, dominated by phonon‐coupled and defect‐mediated polaronic states.

[SMe3]2[Bi2Ag2I10], a silver iodido bismuthate with an unusually small band gap

“…1 on the other hand has an optical band gap of 1.82 eV, which is similar to those found in 2D elpasolites, such as [(3AMPY) 2 AgBiI 8 ·H 2 O] (3AMPY = 3-(aminomethyl) pyridinium) 21 and (4FPEA) 4 AgBiI 8 (4FPEA = 4-fluorophenethylammonium) 44 with optical band gaps of 1.86 eV and 1.84 eV, respectively. Importantly, the band gap is significantly smaller than the 2.05 eV and 1.92 eV reported for the aforementioned and structurally very similar [NEt 4 ] 2 [Bi 2 Ag 2 I 10 ] 23 and [1,3,5-Me 3 py] 2 [Bi 2 Ag 2 I 10 ], 26 respectively.…”

Molybdenum chloride double perovskites: dimensionality control of optical and magnetic properties

“… 49 The [AgCl 6 ] 5− polyhedra are highly distorted which is commonly ascribed to preferential formation of linear coordination geometry due to the mixing of filled Ag 4d orbitals with empty Ag 5s orbitals. 50 The 1,4-BDA spacer adopts a gauche conformation ( Fig. 3c ).…”

Establishing Family Relations in Group 15 Halogenido Metalates with the Largest Molecular Antimony Iodide Anion

“…[16] Differences in material preparation, measurement methods and setups typically contribute to the observation of such different values, for example between microcrystalline powders and thin films. [17] In compounds containing [SbI 4 ] À anions as chains of cis-connected octahedra forming a zigzag chain, optical band gaps between 1.79 and 2.41 eV have been reported. [18] When comparing compounds with the same anion motif but different cations, differences in crystal packing will result.…”