Cesium Lead Bromide Perovskite Nanocrystals Research Articles

Surface-Engineered Cesium Lead Bromide Perovskite Nanocrystals for Enabling Photoreduction Activity.

In recent years, colloidal lead halide perovskite (LHP) nanocrystals (NCs) have exhibited such intriguing light absorption properties to be contemplated as promising candidates for photocatalytic conversions. However, for effective photocatalysis, the light harvesting system needs to be stable under the reaction conditions propaedeutic to a specific transformation. Unlike photoinduced oxidative reaction pathways, photoreductions with LHP NCs are challenging due to their scarce compatibility with common hole scavengers like amines and alcohols. In this contribution, it is investigated the potential of CsPbBr3 NCs protected by a suitably engineered bidentate ligand for the photoreduction of quinone species. Using an in situ approach for the construction of the passivating agent and a halide excess environment, quantum-confined nanocubes (average edge length = 6.0 ± 0.8 nm) are obtained with a low ligand density (1.73 ligand/nm2) at the NC surface. The bifunctional adhesion of the engineered ligand boosts the colloidal stability of the corresponding NCs, preserving their optical properties also in the presence of an amine excess. Despite their relatively short exciton lifetime (τAV = 3.7 ± 0.2 ns), these NCs show an efficient fluorescence quenching in the presence of the selected electron accepting quinones (1,4-naphthoquinone, 9,10-phenanthrenequinone, and 9,10-anthraquinone). All of these aspects demonstrate the suitability of the NCs for an efficient photoreduction of 1,4-naphthoquinone to 1,4-dihydroxynaphthalene in the presence of triethylamine as a hole scavenger. This chemical transformation is impracticable with conventionally passivated LHP NCs, thereby highlighting the potential of the surface functionalization in this class of nanomaterials for exploring new photoinduced reactivities.

Cesium lead bromide perovskite nanocrystals for the visual detection of chloride ions: A review

Lead halide perovskite nanocrystals (NCs) have been extensively studied due to their high quantum yield, high color purity, tunable band gap, and simple preparation methods. Among them, cesium lead bromide perovskite NCs (CsPbBr3 NCs) have the characteristics of good stability performance, better luminous performance, and good halide exchange properties, etc., and a visual sensing system for fluorescence wavelength shift can be constructed by using their spectral tunability. Accordingly, CsPbBr3 has become a potential candidate material for on-site detection of chloride ions, providing possibility for tunable visual analysis, which not only expands the application potential of CsPbBr3 NCs in the detection field, but also greatly improves the visual fluorescence sensing method. On a basis of the halide exchange property of CsPbBr3 NCs, this review introduces the development strategy of perovskites as the probes to detect chloride ions in the environments of liquids, solids, and gases, and summarizes and prospects the new methods of chloride detection over CsPbBr3 NCs. In addition, this review provides an overview of existing challenges, providing reference for the development of highly sensitive and long-term stable chloride probes based on lead halide perovskites.

Correlation between Single-Photon Emission and Size of Cesium Lead Bromide Perovskite Nanocrystals.

Emission photon statistics of semiconductor nanocrystal quantum dots (QDs), including lead halide perovskite nanocrystals (PNCs), are important fundamental and practical optical properties. Single QDs exhibit high-probability single-photon emission owing to the efficient Auger recombination between generated excitons. Because the recombination rate depends on QD size, single-photon emission probability should be size-dependent. Previous studies have researched QDs smaller than their exciton Bohr diameters (twice the Bohr radius of excitons). Here, we investigated the relationship between the single-photon emission behavior and size of CsPbBr3 PNCs to elucidate their size threshold. Simultaneous single-nanocrystal spectroscopy and atomic force microscopy observations on single PNCs with approximately 5-25 nm edge length showed that those smaller than approximately 10 nm, which had size-dependent photoluminescence (PL) spectral shifts, exhibited high-probability single-photon emissions, which decreased linearly with PNC volume. Novel single-photon emission, size, and PL peak correlations of PNCs are important for understanding the relationship between single-photon emission and quantum confinement.

Optical and photoelectrical properties of low-concentration-Mn-doped CsPbBr3 nanocrystals

Doping of cesium lead bromide (CsPbBr3) perovskite nanocrystals offers effective control of their optical and optoelectrical properties, leading to possibilities of several new applications. Herein, cesium lead bromide perovskite nanocrystals are synthesized with doping of a low concentration of manganese (Mn) into the perovskite lattice using manganese (II) chloride (MnCl2) as a precursor. The shift in X-ray diffraction peaks toward higher angles indicates that manganese as a dopant is present inside the cesium lead bromide lattice. A change in the manganese (II) chloride precursor concentration from 5 to 10 mmol results in an increment in the atomic percentage of manganese from 0.3 to 0.5% in the cesium lead bromide crystal. Doping of a low concentration of manganese (0.3 at.%) into cesium lead bromide results in enhancement of green emission, while doping with a higher concentration of manganese (0.5 at.%) results in blue emission. The band gap of cesium lead bromide nanocrystals increases from 2.31 to 2.53 eV with an increase in the concentration of manganese. The dark and photoelectrical conductivity of cesium lead bromide nanocrystals is improved in the case of doping with a low concentration (0.3 at.%) of manganese. The ratio of photocurrent against dark current is found to be ∼182 in manganese-doped cesium lead bromide crystal film as compared with ∼101 for undoped cesium lead bromide crystal film. Doping with a low concentration of manganese improves the overall electrical and photoelectrical conductivity of cesium lead bromide perovskite nanocrystals.

Water-induced nucleation growth kinetics enhancement of cesium lead bromide perovskite nanocrystals

Water-induced nucleation growth kinetics enhancement of cesium lead bromide perovskite nanocrystals

Slower Auger Recombination in 12-Faceted Dodecahedron CsPbBr3 Nanocrystals.

Over the past two decades, intensive research efforts have been devoted to suppressions of Auger recombination in metal-chalcogenide and perovskite nanocrystals (PNCs) for the application of photovoltaics and light emitting devices (LEDs). Here, we have explored dodecahedron cesium lead bromide perovskite nanocrystals (DNCs), which show slower Auger recombination time compared to hexahedron nanocrystals (HNCs). We investigate many-body interactions that are manifested under high excitation flux density in both NCs using ultrafast spectroscopic pump-probe measurements. We demonstrate that the Auger recombination rate due to multiexciton recombinations are lower in DNCs than in HNCs. At low and intermediate excitation density, the majority of carriers recombine through biexcitonic recombination. However, at high excitation density (>1018 cm-3) a higher number of many-body Auger process dominates over biexcitonic recombination. Compared to HNCs, high PLQY and slower Auger recombinations in DNCs are likely to be significant for the fabrication of highly efficient perovskite-based photonics and LEDs.

Photostability of amine-free CsPbBr3 perovskite nanocrystals under continuous UV illumination

In this work, we verified that light induces a dynamic equilibrium between ligands and the inorganic surface in amine-free perovskite nanocrystals, and we demonstrated that oleylphosphate ligands can improve the photostability of cesium lead bromide perovskite nanocrystals.

Stabilizing and accessing across ternary phase cesium lead bromide perovskite nanocrystals: thermodynamic and kinetic controls

Lead halide perovskites with fascinating optoelectronic properties have enabled rapid advancement and development in photovoltaics and light-emitting diodes. However, accessing and stabilizing the complex ternary phase space diagram (Cs-Pb-Br) of perovskites including 3 D nanocrystals, 2 D nanoplatelets, and 0 D hexagonal platelets with desirable optoelectronic properties further requires a deeper understanding of the thermodynamic and kinetic aspects regarding the growth of lead halide perovskite nanocrystals. In this work, we have mapped out the multivariant synthetic design spaces observed in the ternary phase diagram of Cs-Pb-Br to evaluate the effect of controlling thermodynamic equilibrium state (e.g. chemical potentials of the Cs:Pb ratio) and growth kinetics with ligand concentration (oleylamine). Further in-situ tracking of reversible phase transformation with the addition of oleylamine (forward) and PbBr2 (reverse) exhibiting distinctive spectroscopic signatures between 3 D and 0 D phases (vice versa) can provide insight into the reversible phase transformation mechanism and important role of PbBr2 species that can modify the bonding motif and connectivity of [PbBr6]4- octahedral frameworks.

Unraveling the role of hydrogen bromide in the growth of cesium lead bromide perovskite nanocrystals

Hydrogen bromide (HBr) could substantially improve the quality of cesium lead bromide perovskite (CsPbBr3) nanocrystals (NCs) and greatly enhance their optoelectronic performance. However, clarifying the role of HBr in the growth of CsPbBr3 NCs has been a substantial challenge thus far. Herein, we design an in situ cryogenic photoluminescence system using liquid nitrogen to unravel the role played by HBr in the growth of CsPbBr3 NCs. Compared with no HBr (∼40 s), HBr improves the nucleation rate of CsPbBr3 NCs about two times (∼20 s), and its emission peak also exhibits a redshift of ∼30 nm. Thus, we conclude that HBr accelerates the nucleation rate of CsPbBr3 NCs and extends their growth stage, affording the generation of large grains. Perovskite light-emitting diodes based on CsPbBr3 NCs with added HBr also exhibit an outstanding performance. These outcomes provide new insights into the role of HBr in CsPbBr3 NCs and help prepare high-quality CsPbBr3 NCs for use in the fabrication of efficient CsPbBr3 NC-based optoelectronic devices.

Colorimetric paper test strips based on cesium lead bromide perovskite nanocrystals for rapid detection of ciprofloxacin hydrochloride

The detection of drugs containing hydrochloric salt with conventional methods is time consuming and expensive. In this work, upon exposure to ciprofloxacin hydrochloride at different concentrations, the emission from CsPbBr3 NCs shifts to the blue from 513 nm to 442 nm. CsPbBr(3−x)Cl x NCs are formed by the ion exchange and substitution of Br− and Cl− ions from surface to core of NCs. The first-principles calculations suggest that the substitution of Br− by Cl− ions plays a critical role in the tuning of the energy bandgap. The color of paper test strips changes immediately after exposure to different Ciproxan solutions. We propose that this rapid and portable method has a high potential application in other chloride salts for food safety.

Wavelength Tunable Aqueous CsPbBr3-Based Nanoprobes with Ultrahigh Photostability for Targeted Super-Resolution Bioimaging.

Single molecule localization microscopy (SMLM) is indispensable in the visualization of cellular microstructures. However, current SMLM imaging materials, from organic fluorophores to quantum dots, still lack the requirement of increasing need for multiple targets of interest due to their broad emission. Here, by one-step encapsulating hydrophilic cesium lead bromide perovskite nanocrystals (CsPbBr3 NCs) into functionalized polyethylene glycol (PEG), a core-shell nanocomposite of CsPb(Cl(1-x)/Brx)3@PEG (0 < x < 1) was presented as a wavelength-tunable fluorescent probe with the narrow full width at half-maximum (fwhm) as 11 nm. The layer of functionalized PEG endows CsPbBr3 NCs with a broad spectral tunability from 521 to 431 nm, superior photostability for several years, and the ability to be further surface functionalized. The CsPb(Cl(1-x)/Brx)3@PEG exhibits a sub-10 nm localization precision and 10-fold enhanced spatial resolution. Using exosomes with small sizes less than 150 nm as the imaging target, CsPb(Cl(1-x)/Brx)3@PEG realized the distinction of two adjacent exosomes by SMLM. Moreover, after being modified with biotin, CsPb(Cl(1-x)/Brx)3@PEG was universally used for SMLM imaging of cellular microstructures. The excellent photostability and narrow fwhm indicated that such a CsPbBr3-based nanoprobe has great potential as a commercial dye for multitarget super-resolution bioimaging applications.

Probing the effect of a glass network on the synthesis and luminescence properties of composite perovskite glasses [Invited

All-inorganic cesium lead bromide perovskite nanocrystals (PNCs) are highly promising candidates for various optoelectronic and photonic devices. However, poor stability upon exposure to moisture and lead toxicity issues significantly limit their applications. A modern and promising strategy on resolving these issues is the encapsulation of highly luminescent (PNCs) within transparent inorganic oxide glasses. While the encapsulation procedure effect on the development and properties of the so-formed PV-Glasses has been explored in detail, there is lack of understanding the influence of the selected glass composition and network type on the outcome of the synthesis. Herein we report on the synthesis and photoluminescence properties of composite perovskite-glasses upon growing all-inorganic lead halide perovskites within three different types of inorganic oxide glasses. When a silver metaphosphate glass matrix is used it is revealed that the low glass transition temperature of the phosphate glass limits significantly the temperature range of the required post-melting annealing treatment, while the lead salt precursors react with the phosphate entities of the network destroying the stoichiometry of the PNCs. As a result the formation of PNCs is hindered. As a consequence, a double network former borophosphate glass was employed as a suitable host. While annealing treatments at higher temperature were facilitated in this case, it is found that the high silver content becomes an obstacle for the perovskite formation. In view of these findings, cesium lead bromide (CsPbBr3) and cesium lead iodide (CsPbI3) composite perovskite borate glasses were synthesized and found to be suitable hosts. Indeed, such composite glasses exhibit interesting photoluminescence properties that are compared with those of PNCs outside the glass matrix.

Corrigendum: Cesium Lead Bromide Perovskite Nanocrystals as a Simple and Portable Spectrochemical Probe for Rapid Detection of Chlorides

Corrigendum: Cesium Lead Bromide Perovskite Nanocrystals as a Simple and Portable Spectrochemical Probe for Rapid Detection of Chlorides

Cesium Lead Bromide Perovskite Nanocrystals as a Simple and Portable Spectrochemical Probe for Rapid Detection of Chlorides

AbstractThe wide spectral tunability of CsPbBr3 perovskite nanocrystals (NCs) via instantaneous and facile anion exchange, make them a suitable candidate for chloride detection. Rapid anion‐exchange processes between CsPbBr3 perovskite NCs and different chloride solutions were carried out in ambient conditions. The resultant anion‐exchanged CsPbCl3‐xBrx NCs preserved the structural properties and exhibited a remarkable blue‐shift in photoluminescence spectra. This form a basis for detection of chloride ions in water. This has been applied with the limit of detection upto 100 μM. The detection strategies were not only limited to the direct addition of chloride solutions to NCs, but also showed a visual colour change under UV light when the chloride solution is drop‐casted on CsPbBr3 films that are deposited on glass substrates. Furthermore, the detection strategy is established by drop‐casting CsPbBr3 NCs onto paper strips that are pre‐soaked in chloride solutions. A considerable blue‐shift in fluorimetry proves them to be an excellent sensing medium as practical spectrochemical probes for on‐site detection of chlorides. Based on this, a colour chart and selectivity chart to access the presence of chlorides and their concentration is demonstrated here.

Inorganic Ruddlesden-Popper Faults in Cesium Lead Bromide Perovskite Nanocrystals for Enhanced Optoelectronic Performance.

While the layered hybrid Ruddlesden-Popper (RP) halide perovskites have already established themselves as the frontrunners among the candidates in optoelectronics, their all-inorganic counterparts remain least explored in the RP-type perovskite family. Herein, we study and compare the optoelectronic properties of all-inorganic CsPbBr3 perovskite nanocrystals (PNCs) with and without RP planar faults. We find that the RP-CsPbBr3 PNCs possess both higher exciton binding energy and longer exciton lifetimes. The former is ascribed to a quantum confinement effect in the PNCs induced by the RP faults. The latter is attributed to a spatial electron-hole separation across the RP faults. A striking difference is found in the up-conversion photoluminescence response in the two types of CsPbBr3 PNCs. For the first time, all-inorganic RP-CsPbBr3 PNCs are tested in light-emitting devices and shown to significantly outperform the non-RP CsPbBr3 PNCs.

Highly stable cesium lead bromide perovskite nanocrystals for ultra-sensitive and selective latent fingerprint detection

Latent fingerprints (LFPs) are one of the most important forms of evidence in crime scenes due to the uniqueness and permanence of the friction ridges in fingerprints. Therefore, an efficient method to detect LFPs is crucial in forensic science. However, there remain several challenges with traditional detection strategies including low sensitivity, low contrast, high background, and complicated processing steps. In order to overcome these drawbacks, we present an approach for developing latent fingerprints using stabilized CsPbBr3 perovskite nanocrystals (NCs) as solid-state nanopowders. We demonstrate the superior optical stability of CsPbBr3 NCs with respect to absorption, photoluminescence (PL), and fluorescence lifetime. We then used these highly stable, fluorescent CsPbBr3 NCs as a powder dusting material to develop LFPs on diverse surfaces. The stable optical properties and hydrophobic surface of the CsPbBr3 NC nanopowder permitted high resolution images from which unique features of friction ridge arrangements with first, second, and third-level LFP details can be obtained within minutes.

Zinc ions doped cesium lead bromide perovskite nanocrystals with enhanced efficiency and stability for white light-emitting diodes

All-inorganic cesium lead halide perovskite nanocrystals (NCs) are considered as an excellent candidate material for light-emitting devices (LED) displays because of their great photo-physical properties. However, the efficiency and stability of these materials are still unsatisfactory, which is the main disadvantage hindering the commercialization of the perovskite NCs based LED displays. On the other hand, the poisonous element lead (Pb) restricted the large-scale application of the perovskite NCs. Here we reported a hot-injection method by doping zinc ions into the CsPbBr3 NCs with enhanced photoluminescence (PL) properties and stability in ambient air. The doped NCs exhibit the highest photoluminescence quantum yield (PLQY) of 91.3% and a narrow full width at half-maximum (FWHM) of 15.5 nm. The improved the optical properties and stability of the doped NCs may result from the enhanced formation energies of perovskite lattices and the surface passivation. Finally, a white light-emitting diode (WLED) was fabricated by combining the green-emitting CsPbBr3:Zn2+ doped NCs and red-emitting K2SiF6:Mn6+ phosphors along with a blue LED chip, which exhibits a luminous efficiency of 36 lm/W, a chromaticity coordinate of (0.327, 0.336), a color temperature (CCT) of 5760 K and a wide color gamut (137% of the National Television System Committee).

Bromopropane as a novel bromine precursor for the completely amine free colloidal synthesis of ultrastable and highly luminescent green-emitting cesium lead bromide (CsPbBr3) perovskite nanocrystals.

Recently, lead halide perovskite nanocrystals (PNCs) have attracted intense interest as promising active materials for optoelectronic devices. However, their extensive applications are still hampered by poor stability under ambient conditions. Oleic acid and oleylamine are the most commonly used ligands in colloidal CsPbX3 (X = Cl, Br, and I) synthesis. Oleylamine plays a dual role as it stabilizes the surface but in the long run or post-synthesis, it may disturb the colloidal stability due to facile proton exchange leading to the formation of labile oleylammonium halide, which detaches the halide ions from the NC surface. To address these issues, herein, we report an open-atmospheric, facile, efficient, and completely amine-free synthesis of cesium lead bromide perovskite nanocrystals using a novel bromine precursor, bromopropane, which is inexpensive and available at hand. The reaction mechanism follows a trioctylphosphine/oleic acid-mediated surface passivation route that provides an amine-free reaction environment to stabilize ligand capping on the NC surface. Uniform, highly monodisperse NCs of size ∼29 nm were obtained. The as-synthesized NCs have a high photoluminescence quantum yield (PLQY) of around 80%, and especially, exhibited strong stability under ambient conditions and continuous UV irradiation. The PLQY can maintain 83% of the initial one even after 120 days. Furthermore, after 96 h of continuous irradiation under UV light at 365 nm (8 W cm-2) under open ambient conditions, the photoluminescence (PL) intensity showed retention of 68% of its original value with no significant changes in the full width at half-maximum, whereas the amine-based sample retains only 5% of its original PL intensity. Furthermore, we have utilized these NCs to fabricate stable down-converted LED devices. The present work demonstrated the synthesis of ultra-stable CsPbBr3 NCs that can be an ideal candidate for display applications.

Size-tunable and stable cesium lead-bromide perovskite nanocubes with near-unity photoluminescence quantum yield.

Stable cesium lead bromide perovskite nanocrystals (NCs) showing a near-unity photoluminescence quantum yield (PLQY), narrow emission profile, and tunable fluorescence peak in the green region can be considered the ideal class of nanomaterials for optoelectronic applications. However, a general route for ensuring the desired features of the perovskite NCs is still missing. In this paper, we propose a synthetic protocol for obtaining near-unity PLQY perovskite nanocubes, ensuring their size control and, consequently, a narrow and intense emission through the modification of the reaction temperature and the suitable combination ratio of the perovskite constituting elements. The peculiarity of this protocol is represented by the dissolution of the lead precursor (PbBr2) as a consequence of the exclusive complexation with the bromide anions released by the in situ SN2 reaction between oleylamine (the only surfactant introduced in the reaction mixture) and 1-bromohexane. The obtained CsPbBr3 nanocubes exhibit variable size (ranging from 6.7 ± 0.7 nm to 15.2 ± 1.2 nm), PL maxima between 505 and 517 nm, and near-unity PLQY with a narrow emission profile (fwhm of 17–19 nm). Additionally, the NCs synthesized with this approach preserve their high PLQYs even after 90 days of storage under ambient conditions, thus displaying a remarkable optical stability. Through the rationalization of the obtained results, the proposed synthetic protocol provides a new ground for the direct preparation of differently structured perovskite NCs without resorting to any additional post-synthetic treatment for improving their emission efficiency and stability.

Completely Amine-Free Open-Atmospheric Synthesis of High-Quality Cesium Lead Bromide (CsPbBr3 ) Perovskite Nanocrystals.

Cesium lead halide perovskite nanocrystals (NCs) CsPbX3 (X=Cl, Br, and I) have been prominent materials in the last few years due to their high photoluminescence quantum yield (PLQY) for light-emitting diodes and other significant applications in photovoltaics and optoelectronics. In colloidal CsPbX3 synthesis, the most commonly used ligands are oleic acid and oleylamine. The latter plays an important role in surface passivation but may also be responsible for poor colloidal stability as a result of facile proton exchange leading to the formation of labile oleylammonium halide, which pulls halide ions out of the NC surface. Herein, a facile, efficient, completely amine-free synthesis of cesium lead bromide perovskite nanocrystals using hydrobromic acid as halide source and tri-n-octylphosphane as ligand under open-atmospheric conditions is demonstrated. Hydrobromic acid serves as labile source of bromide ion, and thus this three-precursor approach (separate precursors for Cs, Pb, Br) gives more control than a conventional single-source precursor for Pb and Br (PbBr2 ). The use of HBr paved the way to eliminate oleylamine, and thus the formation of labile oleylammonium halide can be completely excluded. Various Cs:Pb:Br molar ratios were studied and optimum conditions for making very stable CsPbBr3 NCs with high PLQY were found. These completely amine-free CsPbBr3 perovskite NCs synthesized under bromine-rich conditions exhibit good stability and durability for more than three months in the form of colloidal solutions and films, respectively. Furthermore, stable tunable emission across a wide spectral range through anion exchange was demonstrated. More importantly, this work reports open-atmosphere-stable CsPbBr3 NCs films exhibiting strong PL, which can be further used for optoelectronic device applications.