Engineering the Optical Emission and Robustness of Metal‐Halide Layered Perovskites through Ligand Accommodation

Abstract

opportunities for structural engineering by the diverse choices of chemical composition, [3] and thus, interlayer spacing, and lattice distortions. Ultimately, a controlled variation of these parameters could effectively guide the tailoring of the electronic band structure of RPLP semiconductors. In this context, metal-halide RPLP are of particular interest, as they manifest unique properties, such as quantum and dielectric confinement, [4] narrow-and broadband emission, [5,6] fast radiative recombination, [7] long carrier diffusion lengths, [8] and large exciton binding energies. [9] These properties come along with low-cost processing and simplified device architectures. Besides, the presence of the organic layers provides structural stability and protection from moisture, making them more robust against environmental conditions, which is critical for device performance and lifetime. [10] Due to the stacking configuration of RPLP-with relatively strong organicinorganic interconnectivity-the type of organoammonium molecule plays a fundamental role in their photophysics. [11] For example, by introducing phenethylammonium in the Pb-Br system, the resulting RPLP can show four times higher emission efficiency in the deep blue region compared to butylammonium, a behavior that is related to the high lattice rigidity provided by Pb-Br-π stacking and reduced electron-phonon interaction in the phenethylammonium-basedThe unique combination of organic and inorganic layers in 2D layered perovskites offers promise for the design of a variety of materials for mechatronics, flexoelectrics, energy conversion, and lighting. However, the potential tailoring of their properties through the organic building blocks is not yet well understood. Here, different classes of organoammonium molecules are exploited to engineer the optical emission and robustness of a new set of Ruddlesden-Popper metal-halide layered perovskites. It is shown that the type of molecule regulates the number of hydrogen bonds that it forms with the edge-sharing [PbBr 6 ] 4octahedra layers, leading to strong differences in the material emission and tunability of the color coordinates, from deep-blue to pure-white. Also, the emission intensity strongly depends on the length of the molecules, thereby providing an additional parameter to optimize their emission efficiency. The combined experimental and computational study provides a detailed understanding of the impact of lattice distortions, compositional defects, and the anisotropic crystal structure on the emission of such layered materials. It is foreseen that this rational design can be extended to other types of organic linkers, providing a yet unexplored path to tailor the optical and mechanical properties of these materials and to unlock new functionalities.

Correlating Symmetries of Low‐Frequency Vibrations and Self‐Trapped Excitons in Layered Perovskites for Light Emission with Different Colors

“…We note that with the primary ammoniums we obtained stable layered perovskites already by using molecules with short aliphatic chains (butylammonium (BA) with 4 carbon segments (4C)), while for secondary ammoniums longer aliphatic chains of at least 10C were needed to form a stable layered structure, as reported in our previous work. [ 8 ] Thus, we discuss single layer lead‐bromide 2DLPs with BA (4C) and UDA (undecylammonium, 11C) as primary ammoniums, and with N‐MDA (N‐methyldecylammonium, 10C) and N‐MDDA ( N ‐methyldodecylammonium, 12C) as secondary ammoniums. Figure shows the crystallographic structure and photoluminescence (PL) spectra of (BA) 2 PbBr 4 , (UDA) 2 PbBr 4 , (DA) 2 PbBr 4 ), and (N‐MDDA) 2 PbBr 4 (see Section S1 in the Supporting Information for details).…”

“…[ 34,35 ] The organic layer determines the distortions of the inorganic layer, and thereby influences the optical and vibrational properties of the 2DLPs. [ 8,28,29,36 ] Vibrational bands related to the organic moieties that appear at higher frequencies can also impact the band edge emission process. [ 33,37 ]…”

Free and self-trapped exciton emission in perovskite CsPbBr3 microcrystals

“…White-light emitting devices have been developed based on the broad STE emission and a series of halide perovskite materials have been designed and synthesised for highly efficient STE emission. [34][35][36][37][38][39] The double perovskites and low-dimensional perovskites were found to have strong STE emission. [40][41][42][43][44][45][46][47][48] Since the lattice deformation in these structures is easy to occur.…”

Single‐Component White‐Light Emitters with Excellent Color Rendering Indexes and High Photoluminescence Quantum Efficiencies

“…[ 7 ] However, single band Gaussian‐shaped emission derived from excited‐state structural reorganization in organic metal halides, is not broad enough, cannot cover the whole visible spectrum. [ 5,8 ] Dual‐band emission features a primary broad low‐energy emission originated from STEs and a secondary narrow high‐energy band edge emission from free excitons (FEs), [ 4a,9 ] making it possible to generate white‐light emission in single‐component organic metal halides by selecting suitable organic cations, [ 10 ] especially in the corrugated and layered 2D [2,4a,9] and chained 1D [ 6c ] lead halide perovskites. In addition, the dual‐band emissions of silver‐based halides are composed of a small STEs emission and a dominated broadband DBEs emission with very fast nanosecond lifetimes and mediocre PLQEs.…”