Morphology-Dependent Ambient-Condition Growth of Perovskite Nanocrystals for Enhanced Stability in Photoconversion Device

Modulating Activity of Lattice Oxygen of ABO3 Perovskite Oxides in Redox Reactions: A Review

Perovskites, owing to their unique structure, tunable chemical composition, and versatile physicochemical properties, have garnered extensive applications, particularly in redox reactions where the lattice oxygen and/or oxygen vacancies within perovskite are identified as active sites. The modulation of lattice oxygen activity in perovskites is crucial for enhancing the performance of perovskite-type oxides in redox reactions. This review delineates the key factors affecting lattice oxygen activity, including lattice distortions, crystal defects, surface and interface effects, and the migration rate of oxygen ions, and elucidates how these factors synergistically influence the activity of lattice oxygen. A range of strategic approaches, including ionic doping, surface modification, and metal exsolution, are proposed to effectively regulate the behavior and catalytic properties of lattice oxygen. In this investigation, we consolidate a series of analytical and testing methodologies, such as XRD, XPS, ECR, EIS, and TGA, among others, with a focus on lattice oxygen activity, to reveal the fundamental relationship between lattice oxygen activity and the structural and functional attributes of perovskite oxygen carriers. This comprehensive review offers profound insights and guidance for the strategic design and performance optimization of perovskite catalysts or oxygen carriers.

Light-induced transformation of all-inorganic mixed-halide perovskite nanoplatelets: ion migration and coalescence

When exposed to light, the colloidal perovskite nanoplatelets (NPLs) in the film can fuse into larger grains, and this phenomenon was thought to be closely related to ion migration. However, the available CsPbBr3 NPLs are not conducive to directly distinguishing this hypothesis. Herein, we prepare mixed-halide perovskite CsPbBr2.7I0.3 NPLs by a ligand-assisted reprecipitation method and investigate the photoluminescence evolution of NPLs under laser irradiation. At a low-irradiation intensity, 4.5-monolayer NPLs exhibit blue-shifted photoluminescence peaks due to the migration of iodide ions. Under higher laser fluence, a new photoluminescence component appears in the long wavelength region after the spectral blue shift, which is attributed to the coalescence of NPLs according to transmission electron microscopy analysis. A similar spectral evolution is also observed in 8-monolayer NPLs, while only the spectral blue shift caused by ion migration is detected in cuboidal CsPbBr2.7I0.3 nanocrystals. The use of strong bonding ligands can inhibit the fusion process of the NPLs, but not to impede ion migration, suggesting that fusion requires ligand detachment rather than ion migration. Similar suppression effects can be achieved in a vacuum atmosphere. Moreover, we demonstrate that mixed-halide NPLs can be used to realize anti-counterfeiting applications with superior photosensitivity.

Controlled Growth of Perovskite Nanocrystals on Nanotubes via a Nanoseeding Intermediate Stage: Toward Novel Optoelectronic Applications

CsPbBr3 perovskite nanocrystals (CNCs) were densely anchored on multiwalled carbon nanotubes (MWNTs) via a nanoseeding intermediate stage, in which lead-based nuclei are formed on the nanotube surface. After the formation of the intermediate, a cesium precursor was added to promote the growth of CNCs from the surface nuclei and to thereby obtain CNC-decorated MWNT nanohybrids (CMNHs). The morphology and properties of the CMNHs were determined by the reaction temperature employed during their synthesis. Importantly, the use of MWNTs promoted the formation of larger CNCs that emitted intense green light and modified the electronic structure and bandgap energy of the CNCs. Consequently, the CMNHs could function as optoelectronic transducers and exhibit a "turn-on" photocurrent response when exposed to UV light of narrow specific-range wavelengths. In a novel approach for preventing counterfeit products, the CMNHs were used as a light-emitting black ink to create quick-response codes with fake pixels.

Rapid and Direct Liquid-Phase Synthesis of Luminescent Metal Halide Superlattices

The crystallization of nanocrystal building blocks into artificial superlattices has emerged as an efficient approach for tailoring the nanoscale properties and functionalities of novel devices. To date, ordered arrays of colloidal metal halide nanocrystals have mainly been achieved by using post-synthetic strategies. Here, a rapid and direct liquid-phase synthesis is presented to achieve a highly robust crystallization of luminescent metal halide nanocrystals into perfect face-centered-cubic (FCC) superlattices on the micrometer scale. The continuous growth of individual nanocrystals is observed within the superlattice, followed by the disassembly of the superlattices into individually dispersed nanocrystals owing to the highly repulsive interparticle interactions induced by large nanocrystals. Transmission electron microscopy characterization reveals that owing to an increase in solvent entropy, the structure of the superlattices transforms from FCC to hexagonal close-packed (HCP) and the nanocrystals disassemble. The FCC superlattice exhibits a single and slightly redshifted emission, due to the reabsorption-free property of the building block units. Compared to individual nanocrystals, the superlattices have three times higher quantum yield with improved environmental stability, making them ideal for use as ultrabright blue-light emitters. This study is expected to facilitate the creation of metamaterials with ordered nanocrystal structures and their practical applications.

Tiny spots to light the future: advances in synthesis, properties, and application of perovskite nanocrystals in solar cells

Perovskites are in the hotspot of material science and technology. Outstanding properties have been discovered, fundamental mechanisms of defect formation and degradation elucidated, and applications in a wide variety of optoelectronic devices demonstrated. Advances through adjusting the bulk-perovskite composition, as well as the integration of layered and nanostructured perovskites in the devices, allowed improvement in performance and stability. Recently, efforts have been devoted to investigating the effects of quantum confinement in perovskite nanocrystals (PNCs) aiming to fabricate optoelectronic devices based solely on these nanoparticles. In general, the applications are focused on light-emitting diodes, especially because of the high color purity and high fluorescence quantum yield obtained in PNCs. Likewise, they present important characteristics featured for photovoltaic applications, highlighting the possibility of stabilizing photoactive phases that are unstable in their bulk analog, the fine control of the bandgap through size change, low defect density, and compatibility with large-scale deposition techniques. Despite the progress made in the last years towards the improvement in the performance and stability of PNCs-based solar cells, their efficiency is still much lower than that obtained with bulk perovskite, and discussions about upscaling of this technology are scarce. In light of this, we address in this review recent routes towards efficiency improvement and the up-scaling of PNC solar cells, emphasizing synthesis management and strategies for solar cell fabrication.

Nanoparticulate Photoluminescent Probes for Bioimaging: Small Molecules and Polymers

Recent interest in research on photoluminescent molecules due to their unique properties has played an important role in advancing the bioimaging field. In particular, small molecules and organic dots as probes have great potential for the achievement of bioimaging because of their desirable properties. In this review, we provide an introduction of probes consisting of fluorescent small molecules and polymers that emit light across the ultraviolet and near-infrared wavelength ranges, along with a brief summary of the most recent techniques for bioimaging. Since photoluminescence probes emitting light in different ranges have different goals and targets, their respective strategies also differ. Diverse and novel strategies using photoluminescence probes against targets have gradually been introduced in the related literature. Among recent papers (published within the last 5 years) on the topic, we here concentrate on the photophysical properties and strategies for the design of molecular probes, with key examples of in vivo photoluminescence research for practical applications. More in-depth studies on these probes will provide key insights into how to control the molecular structure and size/shape of organic probes for expanded bioimaging research and applications.

Growth of Lead Halide Perovskite Nanocrystals: Still in Mystery

Lead halide perovskite nanocrystals with different halide ions can lead to color-tunable emissions in visible window with near-unity photoluminescence quantum yields. Extensive research has been carried out for optimizing the synthesis of these nanocrystals for the last 6 years, and thousands of research papers have been reported. However, due to the ionic nature, these nanocrystals formed instantaneously and hence, their growth kinetics could not be established yet. In most of the reactions, the formation mechanism typically followed one reaction for one size or shape principle, and their dimension tuning was achieved predominantly with thermodynamic control. There is no clear evidence yet on the decoupling growth from nucleations and monitoring their growth kinetics. Hence, the progress of understanding the fundamentals of crystal growth faced road blocks for these halide perovskite nanocrystals. Keeping eyes on all such reports on one reaction for one size and one reaction for tunable size of the most widely studied CsPbBr₃ nanocrystals, in this perspective, details of their size tunability are analyzed and reported. In addition, comparison of the classical mechanism, obstacles for establishing secondary growth, and possible road maps for controlling the kinetic parameters of formation of these nanocrystals are also discussed.