Metal Halide Perovskite Nanocrystals Research Articles

Present and Perspectives of Photoactive Porous Composites Based on Semiconductor Nanocrystals and Metal-Organic Frameworks.

This review focuses on the recent developments in synthesis, properties, and applications of a relatively new family of photoactive porous composites, integrated by metal halide perovskite (MHP) nanocrystals and metal-organic frameworks (MOFs). The synergy between the two systems has led to materials (MHP@MOF composites) with new functionalities along with improved properties and phase stability, thus broadening their applications in multiple areas of research such as sensing, light-harvesting solar cells, light-emitting device technology, encryption, and photocatalysis. The state of the art, recent progress, and most promising routes for future research on these photoactive porous composites are presented in the end.

Micro–Nanostructure‐Assisted Luminescence in Perovskite Devices

Metal halide perovskite (MHP) materials have demonstrated great advantages over conventional semiconductors for the next‐generation optoelectronics on account of their outstanding photophysical properties and facile solution processability. Among all the related researches, the suitable micro–nanostructures have been proven to be a direct and effective optical and photophysical management strategy, which is essential for improving the luminescent characteristics of MHP‐based luminescent optoelectronics, including light‐emitting diodes (LEDs) and lasers. Herein, the developments of representative optical micro–nanostructures for perovskite luminescence with different architectures are first introduced, including metal nanoparticles, 1D Bragg gratings, 2D nanostructures with and without periodicity, and MHP nanocrystals. Notably, the fabrication techniques of various counterparts in micro–nanostructures are systematically reviewed. Moreover, the recent practical applications of micro–nanostructures in MHP‐based materials and luminescent optoelectronics are discussed in details, which mainly involves localized surface plasmon resonance (LSPR)‐derived luminescence improvement, optical outcoupling manipulation, and stimulated light emission via optical micro–nanocavity. Lastly, the challenges and perspectives for micro–nanostructures toward future's MHP‐based luminescence applications are summarized.

Suppressed phase and structural evolution of CH3NH3PbBr3 microwires to (CH3)2NH2PbBr3 by addition of hydrazine bromide

Organic acids, adopted in the conventional synthetic methods of metal halide perovskite (MHP) nanocrystals (NCs), have shown to accelerate the formation of (CH3)2NH2± cations in the colloidal solution, resulting in the morphological and phase transition of CH3NH3PbBr3 to (CH3)2NH2PbBr3via a reversible acid-base mediated decomposition. Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) analysis demonstrated the formation of (CH3)2NH2± and the complete removal of CH3NH3± cations during the aging process of the colloidal MHP NCs when oleic acid was introduced as a common capping agent. Our results propose a dominant degradation pathway via the deprotonation of CH3NH3± and the subsequent reaction with the residual CH3NH3± by methyl group transfer, leading to the formation of (CH3)2NH2±. Meanwhile, their phase and compositional stability could be significantly improved by introduction of hydrazinium bromide that provides a strong Lewis base suppressing the deprotonation of CH3NH3± cations. Furthermore, the excess Br- anions enable to passivate Br- ion vacancies at the MHP NC surface, which enhances their optoelectronic properties as well as photostability. Thus, these findings provide deep insight into the underlying chemistry associated with the degradation process in the colloidal MHP NCs, which is of fundamental importance for the use of highly stable and defect-free MHP NCs in the optoelectronic devices.

State of the Art and Prospects for Halide Perovskite Nanocrystals.

Metal-halide perovskites have rapidly emerged as one of the most promising materials of the 21st century, with many exciting properties and great potential for a broad range of applications, from photovoltaics to optoelectronics and photocatalysis. The ease with which metal-halide perovskites can be synthesized in the form of brightly luminescent colloidal nanocrystals, as well as their tunable and intriguing optical and electronic properties, has attracted researchers from different disciplines of science and technology. In the last few years, there has been a significant progress in the shape-controlled synthesis of perovskite nanocrystals and understanding of their properties and applications. In this comprehensive review, researchers having expertise in different fields (chemistry, physics, and device engineering) of metal-halide perovskite nanocrystals have joined together to provide a state of the art overview and future prospects of metal-halide perovskite nanocrystal research.

Recent Advances in Synthesis, Properties, and Applications of Metal Halide Perovskite Nanocrystals/Polymer Nanocomposites.

Metal halide perovskite nanocrystals (PNCs) have recently garnered tremendous research interest due to their unique optoelectronic properties and promising applications in photovoltaics and optoelectronics. Metal halide PNCs can be combined with polymers to create nanocomposites that carry an array of advantageous characteristics. The polymer matrix can bestow stability, stretchability, and solution-processability while the PNCs maintain their size-, shape- and composition-dependent optoelectronic properties. As such, these nanocomposites possess great promise for next-generation displays, lighting, sensing, biomedical technologies, and energy conversion. The recent advances in metal halide PNC/polymer nanocomposites are summarized here. First, a variety of synthetic strategies for crafting PNC/polymer nanocomposites are discussed. Second, their array of intriguing properties is examined. Third, the broad range of applications of PNC/polymer nanocomposites is highlighted, including light-emitting diodes (LEDs), lasers, and scintillators. Finally, an outlook on future research directions and challenges in this rapidly evolving field are presented.

Two‐Dimensional Metal Halide Perovskite Nanosheets for Efficient Photocatalytic CO2 Reduction

Metal halide perovskite (MHP) nanocrystals (NCs) have attained ever‐increasing attention in the field of artificial photosynthesis, due to their desirable strong light‐harvesting capacity and long lifetime of photogenerated carriers. However, the well‐known inherent instability and inferior activity of MHP NCs limit their application foreground in photocatalysis. Herein, a series of 2D MHP nanosheets have been synthesized based on a facile approach at room temperature. These 2D materials are used as photocatalysts for the photocatalysis of CO2 reduction without any organic sacrificial agents, which display significantly improved stability compared to traditional MHP NCs in water‐contained reaction system. More importantly, benefitting from the large proportion of low‐coordinated metal atoms and short carrier diffusion distance, these MHP nanosheets exhibit a remarkably increased performance for photocatalytic CO2 reduction. The judicious modulation of halide component endows the MHP nanosheets with a highest electron consumption rate of 87.8 μmol g−1 h−1 among the reported pure MHP catalysts for photocatalytic CO2 conversion, which is over seven times higher than that of traditional MHP NCs.

Surface Defect Engineering of CsPbBr3 Nanocrystals for High Efficient Photocatalytic CO2 Reduction

Converting CO2 into chemical fuels with sunlight is a very attractive approach to solve the greenhouse effect and fossil fuel crisis. Metal halide perovskite nanocrystals (NCs) have been identified as ideal semiconductor photocatalysts for photocatalytic CO2 reduction due to their unique properties, such as strong light absorption, low exciton binding energy, tunable bandgaps, and low cost. However, the pristine perovskite NCs suffering from inevitable defects, which lower their charge transfer efficiency and are detrimental to photocatalytic performance toward CO2 reduction. Herein, a facile approach to modify the surface defects of CsPbBr3 NC is demonstrated using tetrafluoroborate salts as defects treatment agent and loading Co2+ as a cocatalyst. As a result, the optimized Co2+ on the surface of defect‐free CsPbBr3‐BF4 shows a remarkable photocatalytic CO2 activity of 83.8 μmol g−1 h−1, which indicates that the surface modification can effectively suppress the undesired charge recombination in CsPbBr3 NC and promote its charge separation efficiency. This work provides an effective method to modify the surface defects of the CsPbBr3 NCs for high efficient photocatalytic CO2 reduction and broadens the photocatalytic applications of halide perovskites.

Room-Temperature Diffusion-Induced Extraction for Perovskite Nanocrystals with High Luminescence and Stability.

Metal halide perovskite nanocrystals (NCs) serve as a kind of ideal semiconductor for luminescence and display applications. However, the optoelectronic performance and stability of perovskite NCs are mainly subjected to current ligand strategies since these ligands exhibit a highly dynamic binding state, which complicates NC purification and storage. Herein, a method named diffusion-induced extraction is developed for crystallization (DEC) at room temperature, in which silicone oil serves as a medium to separate the solvent from perovskite precursors and diethyl ether promotes the nucleation, leading to highly emissive perovskite NCs. The formation mechanism of NCs using this approach is elucidated, and their optoelectronic properties are fully characterized. The resultant NCs ink exhibits a high photoluminescence quantum yield (PLQY) over 90% with a narrow full width at half maximum of 17nm. The DEC method strengthens the interaction between ligand and NCs via the hydrophobic silicone oil. Therefore, the NCs maintain almost 95% of their initial PLQYs after aging more than seven months in air. The findings will be of great significance for the continued advancement of high PLQY perovskite NCs through a better understanding of formation dynamics. The DEC strategy presents a major step forward for advancing the field of perovskite semiconductor nanomaterials.

Stable zero-dimensional cesium indium bromide hollow nanocrystals emitting blue light from self-trapped excitons

The growing demand for lighting and displays has motivated intensive research in metal-halide perovskite nanocrystals (NCs) recently. However, the development of blue-emissive perovskite NCs lag behind those of green and red ones severely; moreover, the conventional lead-halide perovskites contain toxic element lead. In this study, zero-dimensional Cs3InBr6 NCs with intrinsic broadband blue emission (~ 450 nm) were developed for the first time. Joint experiment-theory characterizations reveal the excited-state structural distortion of [InBr6]3− cluster enables the formation of self-trapped excitons, which contribute the broadband emission. Apart from the solid structure, hollow NCs with controlled particle and pore sizes were obtained resulting from the Ostwald ripening mechanisms. Theoretical calculations show that the easy diffusion of Br vacancies in Cs3InBr6 lattices assist the formation of hollow structure. Encouraged by the remarkable structural and optical stability of hollow Cs3InBr6 NCs, such lead-free NCs may open up new avenues for manufacture of optoelectronic devices.

Chiral-induced spin selectivity enables a room-temperature spin light-emitting diode.

In traditional optoelectronic approaches, control over spin, charge, and light requires the use of both electrical and magnetic fields. In a spin-polarized light-emitting diode (spin-LED), charges are injected, and circularly polarized light is emitted from spin-polarized carrier pairs. Typically, the injection of carriers occurs with the application of an electric field, whereas spin polarization can be achieved using an applied magnetic field or polarized ferromagnetic contacts. We used chiral-induced spin selectivity (CISS) to produce spin-polarized carriers and demonstrate a spin-LED that operates at room temperature without magnetic fields or ferromagnetic contacts. The CISS layer consists of oriented, self-assembled small chiral molecules within a layered organic-inorganic metal-halide hybrid semiconductor framework. The spin-LED achieves ±2.6% circularly polarized electroluminescence at room temperature.

Spin injection sans magnetism

Optoelectronics Light-emitting diodes (LEDs) that emit circularly polarized light (spin-LEDs) have potential applications in in three-dimensional displays, bioencoding, and tomography. The requisite spin polarization of the charge carriers is usually achieved with ferromagnetic contacts and applied magnetic fields, but Kim et al. report on a room-temperature spin-LED that relies instead on a chiral-induced spin selectivity organic layer. This layer selectively injected spin-polarized holes into metal halide perovskite nanocrystals, where they radiatively recombined with unpolarized electrons with an efficiency of 2.6%. Science , this issue p. [1129][1] [1]: /lookup/doi/10.1126/science.abf5291

Recent advances and perspective on the synthesis and photocatalytic application of metal halide perovskite nanocrystals

Metal halide perovskite nanocrystals have attracted great attention of researchers due to their unique optoelectronic properties such as high photoluminescence quantum yield (PLQY), narrow full width at half-maximum (FWHM), long exciton diffusion length and high carrier mobility, which have been widely used in diverse fields including solar cells, photodetectors, light-emitting diodes, and lasers. Very recently, metal halide perovskites have emerged as a new class of materials in photocatalysis due to their promising photocatalytic performance. In this review, we summarize the recent advances on synthesis, modification and functionalization, with a specific focus on the photocatalytic application of metal halide perovskite nanocrystals. Finally, a brief outlook is proposed to point out the challenges in this emerging area. The goal of this view is to introduce the photocatalytic application of the metal halide perovskites and motivate researchers from different fields to explore more potentials in catalysis.

Core/Shell Metal Halide Perovskite Nanocrystals for Optoelectronic Applications

AbstractCore/shell structured metal halide perovskite nanocrystals (NCs) are emerging as a type of material with remarkable optical and electronic properties. Research into this field has been developing and expanding rapidly in recent years, with significant advances in the studies of the shell growth mechanism and in understanding of properties of these materials. Significant enhancement of both the stability and the optical performance of core/shell perovskite NCs are of particular importance for their applications in optoelectronic technologies. In this review, the recent advances in core/shell structured perovskite NCs are summarized. The band structures and configurations of core/shell perovskite NCs are elaborated, the shell classification and shell engineering approaches, such as perovskites and their derivative shells, semiconductor shell, oxide shell, polymer shell, etc. are reviewed, and the shell growth mechanisms are discussed. The prospective of these NCs in lighting and displays, solar cells, photodetectors, and other devices is discussed in the light of current knowledge, remaining challenges, and future opportunities.

Monodispersed CsPb2Br5@SiO2 Core-Shell Nanoparticles as Luminescent Labels for Biosensing.

Despite the rising advances in the field of metal halide perovskite nanocrystals (NCs), the exploitation of such nanoparticles as luminescent labels for ex vivo imaging and biosensing is still unclear and in the early stages of investigation. One of the major challenges toward the implementation of metal halide perovskite NCs in biosensing applications is to produce monodispersed nanoparticles with desired surface characteristics and compatible with aqueous environments. Here, we report the synthesis of monodispersed spherical CsPb2Br5@SiO2 core–shell nanoparticles by post-synthetic chemical transformation of 3D CsPbBr3 NCs in the presence of tetraethyl orthosilicate and a critical water/ammonia ratio. This method involves an ammonia-mediated and ammonia-induced “top-down” transformation of as-synthesized 3D CsPbBr3 NCs to smaller CsPb2Br5 nanoclusters (ca. 2–3 nm), which trigger a seed-mediated silica growth, yielding monodispersed spherical blue luminescent (λemission = 432 nm) CsPb2Br5@SiO2 perovskite nanoparticles. By adjusting the reaction conditions, core–shell nanoparticles of a 36.1 ± 4.5 nm diameter, which preserve their optical properties in water, were obtained. Besides that, the viability of the developed nanoparticles as a luminescent label for biosensing has been proven by specific biorecognition of the IgG protein in a direct immunoassay. Our work sheds light on the chemical processes and transformations involved in the silica nucleation mechanism in the presence of perovskite nanoparticles and opens the way for the future rational design of the next generation of semiconductor NC luminescent biological labels.

Synthesis and Properties of Strongly Quantum-Confined Cesium Lead Halide Perovskite Nanocrystals.

ConspectusSemiconducting metal halide perovskite (MHP) nanocrystals have emerged as an important new class of materials as the source of photons and charges for various applications that can outperform many other semiconductor nanocrystals utilized for the same purposes. However, the majority of the studies of MHP nanocrystals focused on weakly or nonconfined systems, where the quantum confinement giving rise to various size-dependent and confinement-enhanced photophysical properties cannot be explored readily. This was partially due to the challenge in producing strongly quantum-confined MHP nanocrystals, since the traditional kinetic control approach was less effective for the size control. Recent synthetic progress in MHP nanocrystals utilizing the equilibrium-based size control achieved the precise control of quantum confinement with high ensemble uniformity, enabling the exploration of the unique properties of MHP nanocrystals under strong quantum confinement. In this Account, we review the recent progress made in the synthesis of strongly quantum-confined cesium lead halide nanocrystals and investigation of the properties of exciton modified by strong quantum confinement. The main body of this Account discusses the key results of the research in this field in two separate sections. Section 2 describes the thermodynamic equilibrium-based synthesis method to control the size of cesium lead halide perovskite quantum dots in strongly confined regime. Size control in anisotropic nanocrystals with one- and two-dimensional quantum confinement is also discussed. Section 3 covers the following three topics that highlight the effects of quantum confinement on various spectroscopic properties of excitons in cesium lead halide perovskite nanocrystals: (1) Size-dependent absorption cross section of cesium lead halide quantum dots; (2) confinement effect on exciton fine structure and access to the dark exciton exhibiting intense and long-lived photoluminescence; (3) activation of forbidden exciton transition via dynamic lattice distortion by the photoexcited charge carriers enhanced by quantum confinement. The impact of strong quantum confinement goes beyond the properties of excitons covered in this Account and is expected to expand the functionality of MHP nanocrystals as the source of photons and charges. For instance, realization of the possible enhancement of photon down- and upconversion and hot carrier generation via quantum confinement will further increase the usefulness of strongly confined MHP nanocrystals in their applications.

Tuning hole transport layers and optimizing perovskite films thickness for high efficiency CsPbBr3 nanocrystals electroluminescence light-emitting diodes

Metal halide perovskite nanocrystals (NCs) have sparked considerable attentions in the area of light-emitting diodes (LED) by virtue of their remarkable color purity and spectral tunability (400–700 nm). However, the optoelectronic performance of LED devices based on perovskite NCs is severely limited by the problem of charge injection since (i) the charge injection layers exhibit significant differences in energy levels and charge mobility, (ii) one thick NCs emitting layer can obstruct the electrons transmission and one thin NCs emitting layer can change the charge recombination region, inducing series of troubles in fabrication and application of LED devices. Herein, a series of LED devices based on cesium lead bromide (CsPbBr3) green-emitting perovskite NCs are reported by adopting Poly-N-vinylcarbazole (PVK)/Poly [9,9-dioctylfluoreneco-N-[4-(3-methylpropyl)]diphenylamine] (TFB) and Poly[bis(4-phenyl) (2,4,6-trimethylphenyl)amine] (PTAA) as the hole transport layer (HTL) materials. With the increase of applied voltage, the CsPbBr3 NCs LED device with PTAA as HTL displays better transport characteristics, such as a lower turn-on voltage and a higher luminance, than that of the device with TFB and PVK as HTL. By optimizing the spin-coating craft parameter of the CsPbBr3 NCs layer, an efficient green-emitting CsPbBr3 NCs LED device with maximum luminance of 4531 cd m−2, current efficiency of 14.4 cd A−1, power efficiency of 14.1 lm W−1 and maximum external quantum efficiency of 4.28% was obtained. These results provide an approach for the practical applications of CsPbBr3 NCs electroluminescence LED devices.

Comprehensive defect suppression in perovskite nanocrystals for high-efficiency light-emitting diodes

Electroluminescence efficiencies of metal halide perovskite nanocrystals (PNCs) are limited by a lack of material strategies that can both suppress the formation of defects and enhance the charge carrier confinement. Here we report a one-dopant alloying strategy that generates smaller, monodisperse colloidal particles (confining electrons and holes, and boosting radiative recombination) with fewer surface defects (reducing non-radiative recombination). Doping of guanidinium into formamidinium lead bromide PNCs yields limited bulk solubility while creating an entropy-stabilized phase in the PNCs and leading to smaller PNCs with more carrier confinement. The extra guanidinium segregates to the surface and stabilizes the undercoordinated sites. Furthermore, a surface-stabilizing 1,3,5-tris(bromomethyl)-2,4,6-triethylbenzene was applied as a bromide vacancy healing agent. The result is highly efficient PNC-based light-emitting diodes that have current efficiency of 108 cd A−1 (external quantum efficiency of 23.4%), which rises to 205 cd A−1 (external quantum efficiency of 45.5%) with a hemispherical lens.

Recent Advances and Opportunities of Lead-Free Perovskite Nanocrystal for Optoelectronic Application

Metal halide perovskite nanocrystals (NCs), as a new class of light-emitting and light-harvesting materials, have recently attracted intensive attention for an impressive variety of optoelectronic applications. However, the lead toxicity and poor stability of such materials severely restrict their practical applications and future commercialization. Lead-free perovskite NCs and their derivatives, designed by the reasonable chemical substitution of Pb with other nontoxic elements, are recently booming as an attractive alternative to lead-based counterparts. In this review, we firstly present a comprehensive overview of currently explored lead-free perovskite NCs with an emphasis on their design routes, morphologies, optoelectronic properties, and environmental stability issues. Then, we discuss the preliminary achievements of lead-free perovskite NCs in versatile optoelectronic applications, such as light-emitting devices, solar cells, photodetectors, and photocatalysis. We finish this review with a critical outlook into the currently existing challenges and possible development opportunities of this rapidly evolving field.

Metal halide perovskite nanocrystals: application in high-performance photodetectors

Recently, perovskite nanocrystals (NCs) have become highly promising materials due to their unique optical and electrical properties such as high absorption coefficient, high photoluminescence quantum yield, and long exciton diffusion length.

A general approach to realizing perovskite nanocrystals with insulating metal sulfate shells.

The strategy of constructing the core/shell structure is of great importance in emitting semiconductor nanocrystals. However, the coating on soft metal halide perovskite nanocrystals at the single particle level remains a challenge because of the low compatibility between perovskites and common wide-band-gap semiconductors, such as ZnS and CdS. In addition, using these semiconductors as the shell layer requires high reaction temperatures, which often lead to undesirable chemical transformation. Herein we report a general route to passivate the perovskite nanocrystals by insulating metal sulfate shells. The passivating shell is created around the as-synthesized CsPbBr3 perovskite nanocrystals by initiating the reaction between an organic ammonium sulfate and a variety of metal ions in the presence of ligands. This new method allowed for creating insulating metal sulfate shells with controllable thicknesses and without unwanted chemical transformation. Importantly, these novel core/shell-structured nanocrystals show photoluminescence quantum yields near unity, highly suppressed energy transfer in film and suppressed halide exchange in solution.