Milena P. Arciniegas

Layered hybrid perovskites offer exceptional opportunities for tuning optoelectronic properties through structural design. However, achieving reproducible and controllable functionality requires a detailed understanding of how their structures evolve during synthesis and processing. Here, we demonstrate programmable structural symmetry and emission control in benzylammonium‐based layered lead bromide perovskites through coupled time‐ and temperature‐dependent transformations. Under continuous shaking, the material evolves from orthorhombic platelets to a lower‐symmetry monoclinic phase composed of elongated, grooved microcrystals, accompanied by the emergence of broadband emission associated with exciton self‐trapping in the distorted monoclinic structure. By combining in situ and ex situ structural and optical characterization, we show that this transformation involves both lattice reorganization and redistribution of the organic component, consistent with a combination of distortion‐driven and solution‐mediated mechanisms. Thermal activation induces a reverse pathway toward a higher‐symmetry configuration resembling the original orthorhombic phase, accompanied by recovery of sharp excitonic emission. These results establish a direct link between processing history, metastable structural states, and emission behavior, providing a strategy for programming functional states in structurally soft layered perovskites toward adaptive and reconfigurable optoelectronic materials.

Advances in nanoscale semiconductor materials are enabling next-generation optoelectronic technologies with unprecedented efficiency, spectral control, and device miniaturization. Achieving this potential, however, requires the development of so-called Triple E materials, that is, systems that are environmentally friendly, economically inexpensive, and energetically efficient. Meeting these three criteria simultaneously remains a significant challenge. Metal-halide perovskites have emerged as remarkable semiconductors due to their strong optical absorption, high carrier mobility, long diffusion lengths, defect tolerance, and widely tunable bandgaps. Despite these outstanding properties, their limited ambient and operational stability continues to constrain their large-scale preparation and integration into robust devices.

The versatile structure of organic–inorganic layered perovskites has enabled the fabrication of strongly luminescent material sources with narrow emission. However, although demonstrated to be beneficial for many applications, their structural tunability to achieve broadband emission and thus white light is often limited to changes in the organic cation. Herein, the role of solvent–organic cation interactions on the structural arrangement of the organic and inorganic building blocks in a room‐temperature synthesis is investigated. It is shown that changes in the solvent properties coupled with the molecular configuration of the organic cation can disrupt the conventional platelet‐like shape of layered perovskites, leading to disconnected corner‐sharing ribbons of octahedra, from which micrometer‐elongated crystals with nanoscale grooves are formed. With an 18% white light photoluminescence quantum efficiency, the crystal shape enables localized Mn doping at the groove interfaces. These findings highlight the crucial role of the interaction among solvent molecules and organic cations in shaping the assembly of the structural framework and their optical properties.

Our study that correlates the optical emission dynamics with structural and vibrational properties of the two-dimensional layered perovskites. This provides novel insights on electron–phonon coupling in these materials.

The manipulation of nano-objects through heating is an effective strategy for inducing structural modifications and therefore changing the optoelectronic properties of semiconducting materials. Despite its potential, the underlying mechanism of the structural transformations remains elusive, largely due to the challenges associated with their in situ observations. To address these issues, we synthesize temperature-sensitive CsPbBr₃ perovskite nanoplatelets and investigate their structural evolution at the nanoscale using in situ heating transmission electron microscopy. We observe the morphological changes that start from the self-assembly of the nanoplatelets into ribbons on a substrate. We identify several paths of merging nanoplates within ribbons that ultimately lead to the formation of nanosheets dispersed randomly on the substrate. These observations are supported by molecular dynamics simulations. We correlate the various paths for merging to the random orientation of the initial ribbons along with the ligand mobility (especially from the edges of the nanoplatelets). This leads to the preferential growth of individual nanosheets and the merging of neighboring ones. These processes enable the creation of structures with tunable emission, ranging from blue to green, all from a single material. Our real-time observations of the transformation of perovskite 2D nanocrystals reveal a route to achieve large-area nanosheets by controlling the initial orientation of the self-assembled objects with potential for large-scale applications.

Organic-inorganic Pb-free layered perovskites are efficient broadband emitters and thus are promising materials for lighting applications. However, their synthetic protocols require a controlled atmosphere, high temperature, and long preparation time. This hinders the potential tunability of their emission through organic cations, as is instead common practice in Pb-based structures. Here, we present a set of Sn-Br layered perovskite-related structures that display different chromaticity coordinates and photoluminescence quantum yield (PLQY) up to 80%, depending on the choice of the organic monocation. We first develop a synthetic protocol that is performed under air and at 4 °C, requiring only a few steps. X-ray and 3D electron diffraction analyses show that the structures exhibit diverse octahedra connectivity (disconnected and face-sharing) and thus optical properties, while preserving the organic-inorganic layer intercalation. These results provide key insight into a previously underexplored strategy to tune the color coordinates of Pb-free layered perovskites through organic cations with complex molecular configurations.

Lead-based halide perovskite nanocrystals are highly luminescent materials, but their sensitivity to humid environments and their biotoxicity are still important challenges to solve. Here, we develop a stepwise approach to encapsulate representative CsPbBr₃ nanocrystals into water-soluble polymer capsules. We show that our protocol can be extended to nanocrystals coated with different ligands, enabling an outstanding high photoluminescence quantum yield of ∼60% that is preserved over two years in capsules dispersed in water. We demonstrate that this on-bench strategy can be implemented on an automated platform with slight modifications, granting access to a faster and more reproducible fabrication process. Also, we reveal that the capsules can be exploited as photoluminescent probes for cell imaging at a dose as low as 0.3 μg_Pb/mL that is well below the toxicity threshold for Pb and Cs ions. Our approach contributes to expanding significantly the fields of applications of these luminescent materials including biology and biomedicine.

The 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 [PbBr₆]^4‐ octahedra 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.