Laser-Assisted Fabrication for Metal Halide Perovskite-2D Nanoconjugates: Control on the Nanocrystal Density and Morphology

Two-dimensional metal halide perovskites and their heterostructures: from synthesis to applications

Size- and shape-dependent unique properties of the metal halide perovskite nanocrystals make them promising building blocks for constructing various electronic and optoelectronic devices. These unique properties together with their easy colloidal synthesis render them efficient nanoscale functional components for multiple applications ranging from light emission devices to energy conversion and storage devices. Recently, two-dimensional (2D) metal halide perovskites in the form of nanosheets (NSs) or nanoplatelets (NPls) are being intensively studied due to their promising 2D geometry which is more compatible with the conventional electronic and optoelectronic device structures where film-like components are usually employed. In particular, 2D perovskites exhibit unique thickness-dependent properties due to the strong quantum confinement effect, while enabling the bandgap tuning in a wide spectral range. In this review the synthesis procedures of 2D perovskite nanostructures will be summarized, while the application-related properties together with the corresponding applications will be extensively discussed. In addition, perovskite nanocrystals/2D material heterostructures will be reviewed in detail. Finally, the wide application range of the 2D perovskite-based structures developed to date, including pure perovskites and their heterostructures, will be presented while the improved synergetic properties of the multifunctional materials will be discussed in a comprehensive way.

Laser-Induced Morphological and Structural Changes of Cesium Lead Bromide Nanocrystals

Metal halide perovskite nanocrystals, an emerging class of materials for advanced photonic and optoelectronic applications, are mainly fabricated with colloidal chemistry routes. On the quest for new properties according to application needs, new perovskite systems of various morphologies and levels of doping and alloying have been developed, often also involving post-synthesis reactions. Recently, laser irradiation in liquids has been utilized as a fast method to synthesize or transform materials and interesting laser-induced transformations on nanocrystals were induced. These studies in general have been limited to small nanocrystals (~15 nm). In the case of halide perovskites, fragmentation or anion exchange have been observed in such laser-based processes, but no crystal structure transformations were actually observed or deliberately studied. Nanocrystals are more sensitive to light exposure compared to the corresponding bulk crystals. Additional factors, such as size, morphology, the presence of impurities, and others, can intricately affect the photon absorption and heat dissipation in nanocrystal suspensions during laser irradiation. All these factors can play an important role in the final morphologies and in the time required for these transformations to unfold. In the present work, we have employed a 513 nm femtosecond (fs) laser to induce different transformations in large nanocrystals, in which two phases coexist in the same particle (Cs4PbBr6/CsPbBr3 nanohexagons of ~100 nm), dispersed in dichlorobenzene. These transformations include: (i) the exfoliation of the primary nanohexagons and partial anion exchange; (ii) fragmentation in smaller nanocubes and partial anion exchange; (iii) side-by-side-oriented attachment, fusion, and formation of nanoplatelets and complete anion exchange; (iv) side-by-side attachment, fusion, and formation of nanosheets. Partial or complete Br-Cl anion exchange in the above transformations was triggered by the partial degradation of dichlorobenzene. In addition to the detailed analysis of the various nanocrystal morphologies observed in the various transformations, the structure-photoluminescence relationships for the different samples were analyzed and discussed.

Special Issue: Perovskite Nanostructures: From Material Design to Applications

In the past decade, perovskite materials have attracted great scientific and technological interest due to their interesting opto-electronic properties. Nanostructuring of the perovskites, due to their reduced dimensions are advantageous in offering large surface area, controlled transport and charge carrier mobility, strong absorption and photoluminescence, and confinement effects. These features, together with the unique tunability in composition, shape, and functionalities in addition to the ability to form efficient, low-cost, and light-active structures make the perovskite nanostructures efficient functional components for multiple applications, ranging from photovoltaics and batteries to lasing and light-emitting diodes. The purpose of this Special Issue is to give an overview of the latest experimental findings concerning the tunability in composition, shape, functionalities, growth conditions, and synthesis procedures of perovskite structures and to identify the critical parameters for producing materials with functional characteristics.

On the Role of Cs4PbBr6 Phase in the Luminescence Performance of Bright CsPbBr3 Nanocrystals

CsPbBr3 nanocrystals have been identified as a highly promising material for various optoelectronic applications. However, they tend to coexist with Cs4PbBr6 phase when the reaction conditions are not controlled carefully. It is therefore imperative to understand how the presence of this phase affects the luminescence performance of CsPbBr3 nanocrystals. We synthesized a mixed CsPbBr3-Cs4PbBr6 sample, and compared its photo- and radioluminescence properties, including timing characteristics, to the performance of pure CsPbBr3 nanocrystals. The possibility of energy transfer between the two phases was also explored. We demonstrated that the presence of Cs4PbBr6 causes significant drop in radioluminescence intensity of CsPbBr3 nanocrystals, which can limit possible future applications of Cs4PbBr6-CsPbBr3 mixtures or composites as scintillation detectors.

Highly luminescent and ultrastable cesium lead bromide perovskite patterns generated in phosphate glass matrices

Owing to their exceptional optoelectronic properties, all-inorganic lead halide perovskites offer enormous potential for next generation photonic, light-emitting, and optoelectronic devices. However, their usage is significantly limited by their poor stability upon moisture exposure and lead toxicity issues. Moreover, many of the aforementioned applications rely on the development of confined perovskite patterns of various shapes and periodicities. Here we report a simple and low-temperature method enabling the controlled incorporation of photoluminescent all-inorganic metal halide PNCs into a silver phosphate glass (AgPO3) matrix which is transparent in most of the visible range. The developed fabrication protocol is based on a simple melting encapsulation process in which pre-synthesized perovskite crystals are inserted in the glass matrix, following the initial glass quenching. Using this novel approach, two types of composite perovskite glasses are prepared, one that hosts perovskite isles and the second in which a thin perovskite layer is embedded beneath the glass surface. Both types of composite glasses exhibit remarkable photoluminescence stability when compared to the ambient air-exposed perovskite crystals. More importantly, by means of a simple and fast cw-laser processing technique, we demonstrate the development of encapsulated dotted perovskite micropatterns within the composite perovskite glass. The ability of the proposed system to resolve stability and lead toxicity issues, coupled with the facile formation of highly luminescent perovskite patterns pave the way towards the broad exploitation of perovskite crystals in photonic applications.