General Strategy for Rapid Production of Low-Dimensional All-Inorganic CsPbBr3 Perovskite Nanocrystals with Controlled Dimensionalities and Sizes

Perovskite Light-Emitting Diodes with Quantum Wires and Nanorods

Perovskite materials, celebrated for their exceptional optoelectronic properties, have seen extensive application in the field of light-emitting diodes (LEDs), where research is as abundant as the proverbial "carloads of books." In this review, the research of perovskite materials is delved into from a dimensional perspective, with a focus on the exemplary performance of low-dimensional perovskite materials in LEDs. This discussion predominantly revolves around perovskite quantum wires and perovskite nanorods. Perovskite quantum wires are versatile in their growth, compatible with both solution-based and vapor-phase growth, and can be deposited over large areas-even on spherical substrates-to achieve commendable electroluminescence (EL). Perovskite nanorods, on the other hand, boast a suite of superior characteristics, such as polarization properties and tunability of the transition dipole moment, endowing them with the great potential to enhance light extraction efficiency. Furthermore, zero-dimensional (0D) perovskite materials like nanocrystals (NCs) are also the subject of widespread research and application. This review reflects on and synthesizes the unique qualities of the aforementioned materials while exploring their vital roles in the development of high-efficiency perovskite LEDs (PeLEDs).

Using the Photoluminescence Color Change in Cesium Lead Iodide Nanoparticles to Monitor the Kinetics of an External Organohalide Chemical Reaction by Halide Exchange

In this work, we demonstrate a photoluminescence-based method to monitor the kinetics of an organohalide reaction by way of detecting released bromide ions at cesium lead halide nanoparticles. Small aliquots of the reaction are added to an assay with known concentrations of CsPbI3, and the resulting Br-to-I halide exchange (HE) results in rapid and sensitive wavelength blueshifts (Δλ) due to CsPbBrxI3-x intermediate concentrations, the wavelengths of which are proportional to concentrations. An assay response factor, C, relates Δλ to Br- concentration as a function of CsPbI3 concentration. The observed kinetics, as well as calculated rate constants, equilibrium, and activation energy of the solvolysis reaction tested correspond closely to synthetic literature values, validating the assay. Factors that influence the sensitivity and performance of the assay, such as CsPbI3 size, morphology, and concentration, are discussed.

Ligand-flexible synthesis of strongly confined perovskite nanocrystals: a microwave synthetic approach

Perovskite nanocrystals (PNCs) and their strongly confined versions have traditionally been synthesized via hot injection methods. However, there is a pressing need for a new synthesis method that offers more flexible surface chemistry, improved optical properties, and greater sample stability. Here we explore and exploit the recently introduced microwave (MW) synthesis method, focusing on temperature and coating ligands, including a polymer ligand for which the hot injection method is unsuitable. The optimized microwave synthetic protocols produce PNCs with better exciton definition, lower polydispersity, and stronger ligand attachment than their hot injection counterparts. A variety of characterization techniques were employed to compare the properties of PNCs produced by the hot injection versus microwave methods. Insight into the molecular basis for the improved PNC properties was provided by FTIR and several NMR experiments that revealed the nature of the attachment of different ligands and their interactions with the PNCs. The overall results demonstrate that MW synthesis is a promising alternative to the HI method, particularly if smaller PNCs with strong quantum confinement are desired.

Tailoring CsPbBr3 Growth via Non-Polar Solvent Choice and Heating Methods

This study describes an investigation of the role of non-polar solvents on the growth of cesium lead halide (CsPbX₃ X = Br and I) nanoplatelets. We employed two solvents, benzyl ether (BE) and 1-octadecene (ODE), as well as two nucleation and growth mechanisms, one-pot, facilitated by microwave irradiation (MWI)-based heating, and hot-injection, using convection. Using BE and MWI, large mesoscale CsPbBr₃ nanoplatelets were produced, whereas use of ODE produced small crystallites. Differences between the products were observed by optical spectroscopies, which showed first band edge absorptions consistent with thicknesses of ∼9 nm [∼15 monolayer (ML)] for the BE-CsPbBr₃ and ∼5 nm (∼9 ML) for ODE-CsPbBr₃. Both products had orthorhombic crystal structures, with the BE-CsPbBr₃ revealing significant preferred orientation diffraction signals consistent with the asymmetric and two-dimensional platelet morphology. The differences in the final morphology were also observed for products formed via hot injection, with BE-CsPbBr₃ showing thinner square platelets with thicknesses of ∼2 ML and ODE-CsPbBr₃ showing similar morphologies and small crystallite sizes. To understand the role solvent plays in crystal growth, we studied lead plumbate precursor (PbBr_n^2-n) formation in both solvents, as well as solvent plus ligand solutions. The findings suggest that BE dissolves PbBr₂ salts to a higher degree than ODE, and that this BE to precursor affinity persists during growth.

Ligand-modified synthesis of shape-controllable and highly luminescent CsPbBr3 perovskite nanocrystals under ambient conditions

The intrinsic insights of ligand-modified shape-transformation of CsPbBr3 nanocrystals between nanocubes and nanorods are revealed systematically, which can accelerate their practical applications in the optoelectronic field.

Watching Microwave-Induced Microscopic Hot Spots via the Thermosensitive Fluorescence of Europium/Terbium Mixed-Metal Organic Complexes

The hypothesis of microscopic hot spots is widely used to explain the unique microwave (MW) effect in materials science and chemical engineering, but it has not yet been directly measured. Herein we use Eu/Tb mixed-metal organic complexes as nano thermometers to probe the intrinsic temperature of MW-absorbing particles in MW fields based on the thermosensitive fluorescent spectra. According to the measurements of the temperature gradient at the solid/liquid interphase, we derive an MW-irradiated energy transfer model to predict the extent of microscopic hot spots. The fluorescence results agree with the model predictions that the MW-induced temperature gradient can be enlarged by increasing MW intensity, as well as the dielectric loss and size of particles. Conversely, the increase in the thermal conductivity and the dielectric loss of the liquid lowers the temperature gradient. This study enables control of MW-assisted synthesis and MW-responsive techniques.

Oriented Halide Perovskite Nanostructures and Thin Films for Optoelectronics

Oriented semiconductor nanostructures and thin films exhibit many advantageous properties, such as directional exciton transport, efficient charge transfer and separation, and optical anisotropy, and hence these nanostructures are highly promising for use in optoelectronics and photonics. The controlled growth of these structures can facilitate device integration to improve optoelectronic performance and benefit in-depth fundamental studies of the physical properties of these materials. Halide perovskites have emerged as a new family of promising and cost-effective semiconductor materials for next-generation high-power conversion efficiency photovoltaics and for versatile high-performance optoelectronics, such as light-emitting diodes, lasers, photodetectors, and high-energy radiation imaging and detectors. In this Review, we summarize the advances in the fabrication of halide perovskite nanostructures and thin films with controlled dimensionality and crystallographic orientation, along with their applications and performance characteristics in optoelectronics. We examine the growth methods, mechanisms, and fabrication strategies for several technologically relevant structures, including nanowires, nanoplates, nanostructure arrays, single-crystal thin films, and highly oriented thin films. We highlight and discuss the advantageous photophysical properties and remarkable performance characteristics of oriented nanostructures and thin films for optoelectronics. Finally, we survey the remaining challenges and provide a perspective regarding the opportunities for further progress in this field.

Solvent- and initiator-free fabrication of efficient and stable perovskite-polystyrene surface-patterned thin films for LED backlights

We report a one-pot route for the synthesis of CsPbBr₃ perovskite nanocrystals (PNCs) in styrene to form a glue-like polystyrene (PS) pre-polymer incorporating mono-dispersed PNCs. The pre-polymer enables solvent- and initiator-free fabricating and patterning PNC-PS light down-conversion films for liquid crystal display application. The mechanistic study reveals that the styrene molecules adsorbed on the PNC surface undergo self-initiated polymerization in the pre-polymerization process, forming stable surface capsulation over the PNCs. The PNC-PS pre-polymer and composite film display high photoluminescent quantum yield (PLQY) and resistance to air, light irradiation and water. The micropatterned PNC-PS film with a period of 1000 nm was fabricated through imprinting of the pre-polymer. The micropatterned thin film displays an enlarged viewing angle, improved light distribution and PLQY of >90%. The backlight employing the PNC-PS film displays bright green color and a wide color gamut of >120% NTSC. This solvent-free and one-pot strategy could find promising potential in the development of diverse luminescent nanocomposites to meet the requirements of micro/nano-manufacturing and high performance display application.

Using design of experiment to obtain a systematic understanding of the effect of synthesis parameters on the properties of perovskite nanocrystals

Design of experiments was used to systematically investigate the synthesis of MAPbI₃ nanoparticles in a flow reactor. By controlling the solvents and the ligands, we were able to tune the MAPbI₃ photoluminescence peak between 614 and 737 nm.

Metal Halide Perovskite Nanorods: Shape Matters

Quasi-1D metal halide perovskite nanorods (NRs) are emerging as a type of materials with remarkable optical and electronic properties. Research into this field is rapidly expanding and growing in the past several years, with significant advances in both mechanistic studies of their growth and widespread possible applications. Here, the recent advances in 1D metal halide perovskite nanocrystals (NCs) are reviewed, with a particular emphasis on NRs. At first, the crystal structures of perovskites are elaborated, which is followed by a review of the major synthetic approaches toward perovskite NRs, such as wet-chemical synthesis, substrate-assisted growth, and anion exchange reactions, and discussion of the growth mechanisms associated with each synthetic method. Then, thermal and aqueous stability and the linear polarized luminescence of perovskite NRs are considered, followed by highlighting their applications in solar cells, light-emitting diodes, photodetectors/phototransistors, and lasers. Finally, challenges and future opportunities in this rapidly developing research area are summarized.

CsPbI3 Nanotube Photodetectors with High Detectivity

In the present work, the exploration of photodetectors (PDs) based on CsPbI₃ nanotubes are reported. The as-prepared CsPbI₃ nanotubes can be stable for more than 2 months under air conditions. It is found that, in comparison to the nanowires, nanobelts, and nanosheets, the nanotubes can be advantageous to be used as the functional units for PDs, which is mainly attributed to the enhanced light absorption ability induced by the light trapping effect within the tube cavity. As a proof of concept, the as-constructed PDs based on CsPbI₃ nanotube present an overall excellent performance with a responsivity (R_λ ), external quantum efficiency (EQE) and detectivity of 1.84 × 10³ A W^-1 , 5.65 × 10⁵ % and 9.99 × 10¹³ Jones, respectively, which are all comparable to state-of-the-art ones for all-inorganic perovskite PDs.

Synthetic Evolution of Colloidal Metal Halide Perovskite Nanocrystals

Metal halide perovskite semiconductor nanocrystals have emerged as a lucrative class of materials for many optoelectronic applications. By leveraging the synthetic toolboxes developed from decades of research into more traditional semiconductor nanocrystals, remarkable progress has been made across these materials in terms of their structural, compositional, and optoelectronic control. Here, we review this progress in terms of their underlying formation stages, synthetic approaches, and postsynthetic treatment steps. This assessment highlights the rapidly maturing nature of the perovskite nanocrystal field, particularly with regard to their lead-based derivatives. It further demonstrates that significant challenges remain around precisely controlling their nucleation and growth processes. In going forward, a deeper understanding of the role of precursors and ligands will significantly bolster the versatility in the size, shape, composition, and functional properties of these exciting materials.

Impact of cesium in methylammonium lead bromide perovskites: insights into the microstructures, stability and photophysical properties

The thermal and moisture instabilities of pure organic lead halide perovskites are the foremost concerns towards the commercialization of perovskite solar cells, which can be avoided by introducing an inorganic cation, such as cesium ion (Cs+) at the A-site of the perovskite crystals. In this report, the impacts of substituted Cs+ cations on the inherent properties such as microstructures, morphology, and photophysics of pure methylammonium lead bromide (MAPbBr3) perovskites have been investigated. Successful formation of mixed MA1-xCsxPbBr3 phases (with 0 ≤ x ≤ 1.0) was predicted from the theoretically calculated tolerance factor, which was further supported by the appearance of sharp diffraction peaks in X-ray diffraction (XRD) patterns without any additional peaks in the whole composition range. Substitution of Cs+ ions brings significant lattice contraction in the parent MAPbBr3 crystal due to the ion size disparity in the ionic radii between MA+ and Cs+ ions. We examine the vibrational signatures of the Raman bands related to the organic MA+ and infer the nature of interactions between the organic moiety and the surrounding inorganic cage as a function of Cs concentration. Raman spectroscopic analysis reveals structural distortion due to the altered H-bonding interaction of the N+-HBr- type between MA+ and the PbBr3- octahedral framework as a function of Cs content, which is responsible for the octahedral tilting in Cs substituted MAPbBr3. We also found hindered rotational motions of MA+ in the octahedral cage of mixed cationic systems, resulting in the orientational ordering of MA in the presence of Cs. These results certainly offer highly ordered mixed phase structures and promote superior thermal stability, as evident from the thermogravimetric analysis. The photoluminescence intensity becomes considerably enhanced at increased substitution levels, which highlights the capability of incorporated Cs+ cations in suppressing non-radiative recombination in a pure MA-based crystal, possibly related to the mitigation of trapping. The substitution of Cs+ with MAPbBr3 allows innovative strategies to improve the proficiency of tandem solar cells by modifying their structural and photophysical properties.

Growth of perovskite nanocrystals in poly-tetra fluoroethylene based microsystem: on-line and off-line measurements

Cesium lead halide perovskite nanocrystals are photoelectric nanomaterials that have potential applications in a variety of areas due to their excellent photoelectric and tunable photo luminescent properties. In this work, we investigate the synergetic effects of reaction temperature, reaction-capillary length and flow rate on the growth kinetics of perovskite nanocrystals in a PTFE-based microsystem and the photoluminescence characteristics of the perovskite nanocrystals both on-line and off-line. The on-line measurement finds that increasing the reaction temperature leads to the increase of the wavelength of the PL emission peak of the synthesized nanocrystals and reduces the average size of the perovskite nanocrystals synthesized in long reaction-capillaries. The intensity of the PL emission peak of the nanocrystals synthesized at different reaction temperatures decreases with the increase of the flow rate. The off-line measurement reveals that increasing the flow rate generally leads to the blueshift of the PL emission peaks and the decrease of the average size of the perovskite nanocrystals synthesized at the reaction temperature of 160 °C in the capillary length of 60 cm. Increasing temperature leads to the increase of the emission wavelength of the perovskite nanocrystals from 560 to 608 nm. The temperature dependence of the average size of the synthesized nanocrystals with the same synthesis conditions at different temperatures can be described by the Arrhenius relationship with an activation energy of 8.54 kJ mol^-1. Five different cross-sections of the synthesized perovskite nanocrystals are observed, including rhombus, hexagon, rectangle, square and quadrangle with three of them being observed for the first time.

Metal Halide Perovskite Nanocrystals: Synthesis, Post-Synthesis Modifications, and Their Optical Properties

Metal halide perovskites represent a flourishing area of research, which is driven by both their potential application in photovoltaics and optoelectronics and by the fundamental science behind their unique optoelectronic properties. The emergence of new colloidal methods for the synthesis of halide perovskite nanocrystals, as well as the interesting characteristics of this new type of material, has attracted the attention of many researchers. This review aims to provide an up-to-date survey of this fast-moving field and will mainly focus on the different colloidal synthesis approaches that have been developed. We will examine the chemistry and the capability of different colloidal synthetic routes with regard to controlling the shape, size, and optical properties of the resulting nanocrystals. We will also provide an up-to-date overview of their postsynthesis transformations, and summarize the various solution processes that are aimed at fabricating halide perovskite-based nanocomposites. Furthermore, we will review the fundamental optical properties of halide perovskite nanocrystals by focusing on their linear optical properties, on the effects of quantum confinement, and on the current knowledge of their exciton binding energies. We will also discuss the emergence of nonlinear phenomena such as multiphoton absorption, biexcitons, and carrier multiplication. Finally, we will discuss open questions and possible future directions.

Ultrasonication-assisted synthesis of CsPbBr3 and Cs4PbBr6 perovskite nanocrystals and their reversible transformation

We demonstrate an ultrasonication-assisted synthesis without polar solvent of CsPbBr3 and Cs4PbBr6 perovskite nanocrystals (PNCs) and their reversible transformation. The as-prepared CsPbBr3 PNCs and Cs4PbBr6 PNCs exhibit different optical properties that depend on their morphology, size, and structure. The photoluminescence (PL) emission and quantum yield (QY) of the CsPbBr3 PNCs can be tuned by changing the ultrasound power, radiation time, and the height of the vibrating spear. The optimized CsPbBr3 PNCs show a good stability and high PL QY of up to 85%. In addition, the phase transformation between CsPbBr3 PNCs and Cs4PbBr6 PNCs can be obtained through varying the amount of oleylamine (OAm) and water. The mechanism of this transformation between the CsPbBr3 PNCs and Cs4PbBr6 PNCs and their morphology change are studied, involving ions equilibrium, anisotropic growth kinetics, and CsBr-stripping process.

Improved ultraviolet radiation stability of Mn2+-doped CsPbCl3 nanocrystals via B-site Sn doping

A facile and effective B-site Sn doping strategy is used to grow Mn²⁺-doped CsPbCl₃ (Mn:CsPbCl₃) nanocrystals with enhanced ultraviolet irradiation stability and luminescence properties.

Recent advances in one-dimensional halide perovskites for optoelectronic applications

Metal-halide perovskites have emerged as efficient, low-cost energy materials owing to their remarkable optoelectronic properties. In particular, the dimensionality and morphology of crystallites may have a striking influence on their chemical and physical properties and therefore affect their optoelectronic applications. One-dimensional halide perovskites have superior carrier transportation in one dimension, high crystalline quality, and consequently, high quantum efficiencies and long carrier diffusion lengths, which are important for the performance of perovskite-based nanoscale optoelectronic and photonic devices. In this review, we highlight recent advances in the synthesis of one-dimensional halide perovskites and their unique properties as well as their novel optoelectronic applications. This review aims to provide an overview of the achievements in synthesis techniques and nanoscale optoelectronic applications based on one-dimensional perovskite nanocrystals.

Self-Powered All-Inorganic Perovskite Microcrystal Photodetectors with High Detectivity

Organic-inorganic lead halide perovskite microcrystal (MC) films are attractive candidates for fabricating high-performance large-area self-powered photodetectors (PDs) because of their lower trap state density and higher carrier mobility than their polycrystalline counterparts and more suitability of synthesizing large lateral area films than their single-crystal counterparts. Here, we report on the fabrication of self-powered all-inorganic CsPbBr₃ perovskite MC PDs with high detectivity, using a modified solution synthesis method. The MCs are up to about 10 μm in size, and the MC layer is also about 11 μm in thickness. Under 473 nm laser (100 mW) illumination, the CsPbBr₃ MC PDs show responsivity values of up to 0.172 A W^-1, detectivity values of up to 4.8 × 10¹² Jones, on/off ratios of up to 1.3 × 10⁵, and linear dynamic ranges of up to 113 dB. These performances are significantly better than those of PDs based on polycrystalline perovskite thin films and comparable with those of PDs based on perovskite single crystals.

Continuous low temperature synthesis of MAPbX3 perovskite nanocrystals in a flow reactor

Perovskite nanocrystals prepared at room temperature using a simple flow reactor.

Mass production of Mn2+-doped CsPbCl3 perovskite nanocrystals with high quality and enhanced optical performance

A novel microwave-assisted hot injection strategy for mass production of high quality Mn²⁺:CsPbCl₃ NCs was reported.