Cesium Lead Halide Perovskite Quantum Research Articles

Multi-Functional Ethylene-vinyl Acetate Copolymer Flexible Composite Film Embedded with Indium Acetate-Passivated Perovskite Quantum Dots.

In recent years, all-inorganic cesium lead halide perovskite quantum dots have emerged as promising candidates for various optoelectronic applications, including sensors, light-emitting diodes, and solar cells, owing to their exceptional photoelectric properties. However, their commercial utilization has been limited by stability issues. In this study, we addressed this challenge by passivating the surface defects of CsPbBr3 quantum dots using indium acetate, a metal-organic compound. The resulting CsPbBr3 quantum dots exhibited not only high photoluminescence intensity, but also a remarkably narrow half-peak width of 19 nm. Furthermore, by embedding the CsPbBr3 quantum dots in ethylene-vinyl acetate, we achieved stretchability and significantly enhanced stability while preserving the original luminous intensity. The resulting composite film demonstrated the potential to improve the power conversion efficiency of crystalline silicon solar cells and enabled the creation of excellent white light-emitting diodes with coordinates of (0.33, 0.31). This co-passivation strategy, involving surface passivation and polymer packaging, provides a new idea for the practical application of CsPbBr3 quantum dots.

Synthesis of bright blue fluorescence and water-dispersible cesium lead halide perovskite quantum dots for the selective detection of pendimethalin pesticide

Perovskite quantum dots (PQDs) have garnered a lot of interest because of their exceptional optoelectronic qualities. Halide perovskites are very water-sensitive due to their ionic composition. It has been observed that encapsulating perovskite QDs with organic or inorganic materials improve their stability; nonetheless, they frequently suffer from large aggregation size, limited water solubility, and difficulty in subsequent surface functionalization. Herein, we have reported polystyrene and cetyltrimethylammonium bromide (CTAB) as a novel ligands for the surface modification of CsPbBr3 PQDs for the rapid fluorescence detection of pendimethalin pesticide in aqueous media. The as-fabricated PS-CsPbBr3@CTAB PQDs give blue fluorescence under UV light at 365 nm and exhibit good stability. When excited at 370 nm, fluorescent PS-CsPbBr3@CTAB PQDs display emission intensity at 436 nm. Upon addition of pendimethalin pesticide, the fluorescence of PS-CsPbBr3@CTAB PQDs was dramatically quenched, which yields to fluorescence turn-off. Noticeably, a linear quenching was achieved with increasing concentration of pendimethalin pesticide (5.0–100 μM) with the detection limit of 30.34 nM. Moreover, the as-synthesized PS-CsPbBr3@CTAB PQDs acted as a sensor for accurate assay of pendimethalin in potato and apple with low relative standard deviation values.

Stabilization of CsPbBr3 Nanocrystals via Defect Passivation and Alumina Encapsulation for High-Power Light-Emitting Diodes

The instability of inorganic cesium lead halide perovskite quantum dots (QDs) limits their commercial applications. Here, a streamline surface nanotailoring strategy combining defect passivation and alumina infiltration and encapsulation via atomic layer deposition was employed to improve the luminescence properties and stability of QD films. Didodecyl dimethyl ammonium bromide with oleic acid pretreatment was used to reduce nonradiative recombination and photoluminescence quenching through strong bonding. Al2O3 infiltrated through the gaps between the QDs with ng precision control and formed a dense encapsulation barrier, which separated QDs from the influence of the external environment. The fluorescence lifetime and the overall stability of the obtained QD films were greatly improved, which have application prospects in high-power white light-emitting diodes.

Perovskite quantum dot one-dimensional topological laser

Various topological laser concepts have recently enabled the demonstration of robust light-emitting devices that are immune to structural deformations and tolerant to fabrication imperfections. Current realizations of photonic cavities with topological boundaries are often limited by outcoupling issues or poor directionality and require complex design and fabrication that hinder operation at small wavelengths. Here we propose a topological cavity design based on interface states between two one-dimensional photonic crystals with distinct Zak phases. Using a few monolayers of solution-processed all-inorganic cesium lead halide perovskite quantum dots as the ultrathin gain medium, we demonstrate a lithography-free, vertical-emitting, low-threshold, and single-mode laser emitting in the green. We show that the topological laser, akin to vertical-cavity surface-emitting lasers (VCSELs), is robust against local perturbations of the multilayer structure. We argue that the design simplicity and reduction of the gain medium thickness enabled by the topological cavity make this architecture suitable for low-cost and efficient quantum dot vertical emitting lasers operating across the visible spectral region.

Patterning Perovskite Quantum Dots Using Photopolymerization.

All-inorganic cesium lead halide perovskite quantum dots (QDs) have several potential applications, owing to their unique optical and electronic properties. However, patterning perovskite QDs using conventional methods is difficult because of the ionic nature of QDs. Here, we demonstrate a unique approach, in which perovskite QDs are patterned in polymer films through the photocuring of monomers under patterned light illumination. The pattern illumination creates the transient polymer concentration difference, which drives the QDs to form patterns; hence controlling polymerization kinetics is essential for the generation of the QD pattern. For the patterning mechanism, a light projection system equipped with a digital micromirror device (DMD) is developed; thus, light intensity, an important factor to determine polymerization kinetics, is precisely controlled per position on the photocurable solution, resulting in the understanding of the mechanism and the formation of distinct QD patterns. The demonstrated approach assisted by the DMD-equipped projection system can form desired perovskite QD patterns solely by patterned light illumination, paving the way for the development of patterning methods for perovskite QDs and other nanocrystals.

Improving stability and photoluminescence of CsPbBr3 quantum dots/CMC polymer composite for optoelectronics application

Cesium lead halide perovskite quantum dots (PQDs) are the most promising materials for optoelectronic application due to their high photoluminescence quantum yield. However, the poor stability of these PQDs is the major bottleneck towards commercial applications. There have been several strategies to improve the stability of these PQDs which includes PQDs-polymer composite with limited success. In this article we have synthesized CsPbBr3 quantum dots- Carboxymethylcellulose (CMC) composite for the first time to improve the optoelectronic properties as well as stability of these PQDs compared to pure PQDs. Photoluminescence (PL) is significantly improved while the degradation becomes slower than pure PQDs. There is a slight blue shift of ∼8 nm in the absorption spectrum of PQDs/CMC composite indicating almost negligible bandgap alteration. This is also confirmed by the high-resolution transmission electron microscopy analysis. However, 78 meV increase in quasi-fermi level splitting (QFLS) is observed in PQD/CMC optimum composite indicating reduced non-radiative recombination due to defect passivation.However, excess CMC beyond 0.3 mol% in PQDs reduces the PL intensity possibly due to increased defect states or the structural changes at higher CMC concentrations. This can be also confirmed by analysing the x-ray diffraction peak at (112) which disappears at higher concentration of CMC.

The ammonia detection of cesium lead halide perovskite quantum dots in different halogen ratios at room temperature

Recently, all-inorganic perovskite structured nanomaterials CsPbX3 (X = Cl, Br, I or mixed halogen) quantum dots (QDs) have been developed rapidly in many applications such as photovoltaics, light-emitting diodes, and photoelectric detectors due to their excellent optical and photoelectrical properties. Meanwhile, this hot topic material also shows interesting potential in sensing applications because of the sensitive surface and large specific area. The reversible property in gas sensing makes it a promising material to realize highly sensitive visual gas sensor on the fluorescent signal. However, the influencing mechanism of the phenomenon gas molecules is still controversial in many situations. In this paper, we proposed a series of fluorescence turn-on ammonia gas sensors based on spin-coated CsPbX3 film. The wavelength of the fluorescent signal carrier was modulated by altering the ratio of halogen. By properly selecting the proportion of surface ligands and carefully analyzing the experiment results, we believe the dynamic passivation of ammonia molecule on the surface of perovskite QDs made dominated contribution to the sensing mechanism, and the series of CsPbX3 QDs sensor shared a similar trend at room temperature. In addition, the sensors we prepared exhibit impressive performance in sensitivity, response time, and reversibility, showing a good potential for low cost, high precision, miniaturized gas detection based on the optical signal.

Upconversion Luminescence via Anion Exchange in Perovskite Quantum Dots for Anticounterfeiting Inkjet Printing.

Lanthanide-doped upconversion nanoparticles (UCNPs) and cesium lead halide perovskite quantum dots (PeQDs) are highly compatible with each other: UCNPs produce anti-Stokes upconversion luminescence (UCL) under near-infrared (NIR) excitation and the emissive profiles of PeQDs can be conveniently tuned by varying the halide composition ratio. Therefore, in this study, UCNPs and PeQDs are mixed together, producing colorful UCL under 980 nm laser excitation. In addition, ZnI2 is used to vary the halide composition ratio of PeQDs and manipulate UCL in situ, thus adding more flexibility in UCL regulation. Finally, based on the above-mentioned discussion, a double-encrypted anticounterfeiting pattern is generated via sequentially printing ZnI2 solution and UCNP suspension on an A4 paper. Using PeQDs as the decrypting reagent, under the NIR excitation and decryption channel, the hidden information can be fully decrypted. The combination of UCNPs and PeQDs greatly expands the upconversion possibility, offers more feasibility in UCL regulation, and further promotes the practical applications.

Surface regulation by bifunctional BODIPY to fabricate stable CsPbBr3 for multi-layered optical anti-counterfeiting

Cesium lead halide perovskite quantum dots (QDs) have attracted immense attention for luminescent materials due to their narrow emission bands and color-tunable emission. However, indispensable surface ligands originating from ligand-assisted synthesis strategies severely deteriorate the stability and luminescence properties of QDs since these ligands have a highly dynamic binding. Herein, we used a green fluorescence BODIPY molecule containing thiol (named SH-BDP) to regulate the CsPbBr3 QDs surface by ligand regulation. Density functional theory calculations proved that the SH-BDP molecule could bind to the exposed Pb of CsPbBr3 QDs stronger than traditional ligands to form stable SH-BDP-QDs. Moreover, the SH-BDP fixed on the CsPbBr3 QDs surface can improve water and light resistance. It also served as a knob to tune their luminescence properties and the reversible thermal-stimuli response. Finally, the multi-response property of SH-BDP-QDs was realized under polar solvent or heat along with UV light. In addition, we used the SH-BDP-QDs to create various anti-counterfeiting labels; several luminous modes were achieved under different external stimuli, which improved the quality of the optical anti-counterfeiting labels and ensured information security. This work indicates the immense potential of surface ligand manipulation in improving the stability and multi-stimuli-responsive optical encoding of perovskite quantum dots.

Rapid and facile electrospray preparation of CsPbBr3@PMMA fluorescent microspheres for fluorescent detection of ALP in biological samples

All-inorganic cesium lead halide perovskite quantum dots (QDs) have attracted more attention due to their excellent optoelectronic and photovoltaic properties. However, there are few applications in biochemical detection based on their unique photoluminescence property mainly because of the instability to external stimulus. In this work, we focus on a rapid preparation method of CsPbBr3@poly (methyl methacrylate) (PMMA) fluorescent composite microspheres based on electrospray to protect CsPbBr3 QDs from the external stimuli and stabilize them in aqueous environment. The CsPbBr3@PMMA composite microspheres effectively retained over 70% fluorescence intensity after being immersed in deionized water for 20 days. Based on the effective quenching of CsPbBr3@PMMA composite microspheres by MnO2 nanosheets, we developed a simple, label-free, low-cost, and facile fluorescent detection system for assay of alkaline phosphatase (ALP) in biological samples. The method shows a good linear relationship from 10.0 mU/mL to 100 mU/mL (R2 = 0.998) with the detection limit of 4.85 mU/mL and the recovery range of 95.1–110%. In summary, the PMMA coating can simply and effectively stabilize the CsPbBr3 QDs and preserve the luminescence of the CsPbBr3 QDs. The excellent applicability of the composite microspheres-based fluorescent detection system in human serum samples further demonstrates the potential application in the aqueous phase-based biochemical detection for clinical diagnosis and biomedical research.

Electrochemically Quantifying the Phase Transition of Cesium Lead Halide Perovskite Quantum Dots in Purification.

A good purification strategy for obtaining high-quality and low-cost perovskite QDs ink requires a complete removal of the impurities but with a minimal phase transition of QDs from the perovskite phases to the nonperovskite δ-phase. This pioneering work reports the electrochemical quantification on the phase transition level of CsPbI3 QDs in purification. Cyclic voltammetry of the purified QDs evidenced the formation of a new product in the purification process, which was demonstrated to be the undesired nonperovskite δ-phase by independent structural analysis. The developed electrochemical methodology further enabled the quantification of the extent of the phase transition of the QDs purified using different strategies by simply analyzing the charge associated with the relevant peaks and allowing optimization of the purification. The latter is of vital importance for commercialization and is an essential step for boosting their device performance.

Highly stable CsPbBr3 perovskite quantum dot-doped tellurite glass nanocomposite scintillator.

All-inorganic cesium lead halide perovskite quantum dots (PQDs) appear to be promising scintillators for radiation detection; however, they are suffering from poor stabilities against light, heat, and moisture. Here a strategy of using AgCl as the nucleating agent is developed to facilitate growth of CsPbBr3 PQDs in chemically inert tellurite glasses via controlled crystallization. The PQDs are uniformly dispersed and well protected in the dense glass matrix without aggregation. The nanocomposites thus obtained are featured by excellent optical transparency owing to the unique character of tellurite glass having a refractive index comparable to that of the CsPbBr3 crystal. The X-ray excited radioluminescence properties are comprehensively studied. The results show that CsPbBr3 PQD-doped tellurite glasses are highly stable against continuous X-ray irradiation and repeated heat-cooling cycles (from room temperature up to 573 K) without sacrificing their scintillation properties, thus appearing to be a potential scintillator for long-term practical applications.

One-step preparation of blue-emitting CsPbBr3 quantum dots loaded on natural mineral halloysite nanotube

All-inorganic cesium lead halide perovskite quantum dots (QDs) have attracted widespread attention due to unique photoelectric properties. However, blue-emitting (CsPbClxBr3−x, 0 < x ≤ 3) QDs have poor stability and low photoluminescence quantum yields (PLQY), which limits its application in perovskite based light-emitting diodes (LEDs). The chlorine-free CsPbBr3 QDs have fewer crystal defects and a more stable crystal structure. Here, we prepared CsPbBr3 QDs with adjustable photoluminescence (PL) (489–519 nm) by controlling the reaction temperature and composited it with natural mineral halloysite (Hal) nanotubes. The as-prepared CsPbBr3@Hal (100 °C) have high PL intensity, bright blue emission and enhanced stability. Under an open ambient condition, the CsPbBr3@Hal (100 °C) can still maintain 92.4% of original PL intensity after 60 days of storage. In addition, after 280 h of continuous irradiation with 365 nm UV lamp, its PL intensity still maintained 71%. Finally, a white LED (WLED) fabricated by incorporating the CsPbBr3@Hal (100 °C) and commercial red CaAlSiN3: Eu2+ phosphor on the 395 nm InGaN blue-violet chip showed the CIE chromaticity coordinates of (0.3358, 0.3331). This work provides a new way for the synthesis and application of blue-emitting CsPbBr3 perovskite materials in WLEDs and display devices.

Remarkable photoluminescence enhancement of CsPbBr3 perovskite quantum dots assisted by metallic thin films

Abstract All-inorganic cesium lead halide perovskite quantum dots have recently received much attention as promising optoelectronic materials with great luminescent properties and bright application prospect in lighting, lasing, and photodetection. Although notable progress has been achieved in lighting applications based on such media, the performance could still be improved. Here, we demonstrate that the light emission from the perovskite QDs that possess high intrinsic luminous efficiency can be greatly enhanced by using metallic thin films, a technique that was usually considered only useful for improving the emission of materials with low intrinsic quantum efficiency. Eleven-fold maximal PL enhancement is observed with respect to the emission of perovskite QDs on the bare dielectric substrate. We explore this remarkable enhancement of the light emission originating from the joint effects of enhancing the incident photonic absorption of QDs at the excitation wavelength by means of the zero-order optical asymmetric Fabry–Perot-like thin film interference and increasing the radiative rate and quantum efficiency at the emission wavelength mediated by surface plasmon polaritons. We believe that our approach is also potentially valuable for the enhancement of light emission of other fluorescent media with high intrinsic quantum efficiency.

Achieving Optical Gain of the CsPbBr3Perovskite Quantum Dots and Influence of the Variable Stripe Length Method

High-quality inorganic cesium lead halide perovskite quantum dot (CsPbBr3 PQD) thin films were successfully deposited directly from a powdered source and used as an active laser medium following the examination of their distinctive surface and structural properties. To determine the suitability of the CsPbBr3 PQDs as an active laser medium, amplified spontaneous emission (ASE) and optical gain properties were investigated under picosecond pulse excitation using the variable stripe length (VSL) method. The thin film of CsPbBr3 PQDs has exhibited a sufficient value of the optical absorption coefficient of ∼0.86 × 105 cm–1 near the band edge and a direct band gap energy Eg ∼2.38 eV. The samples showed enhanced emission, and ASE was successfully recorded at a low threshold. The light emitted from the edge was observed near 2.40 and 2.33 eV for the stimulated emission (SE) and ASE regimes, respectively. The nonradiative decay contributes excitons dominant over biexcitons in the sample edge emission above the ASE threshold, making it practical for CsPbBr3 PQDs to be used as optical gain media without undergoing repeated SE processes above the threshold over long periods. A high value of the optical gain coefficient was recorded at 346 cm–1.

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.

Inducing Factors for Precipitation of Cesium Lead Halide Perovskite Quantum Dots from Glass

Inducing Factors for Precipitation of Cesium Lead Halide Perovskite Quantum Dots from Glass

Unraveling the Origin of the Long Fluorescence Decay Component of Cesium Lead Halide Perovskite Nanocrystals.

A common signature of nearly all nanoscale emitters is fluorescence intermittency, which is a rapid switching between “on”-states exhibiting a high photon emission rate and “off”-states with a much lower rate. One consequence of fluorescence intermittency occurring on time scales longer than the exciton decay time is the so-called delayed photon emission, manifested by a long radiative decay component. Besides their dominant fast radiative decay, fully inorganic cesium lead halide perovskite quantum dots exhibit a long fluorescence decay component at cryogenic temperatures that is often attributed to the decay of the dark exciton. Here, we show that its origin is delayed photon emission by investigating temporal variations in fluorescence intensity and concomitant decay times found in single CsPbBr3 perovskite quantum dots. We attribute the different intensity levels of the intensity trace to a rapid switching between a high-intensity exciton state and an Auger-reduced low-intensity trion state that occurs when the excitation is sufficiently strong. Surprisingly, we observe that the exponent of this power-law-dependent delayed emission is correlated with the emission intensity, which cannot be explained with existing charge carrier trapping models. Our analysis reveals that the long decay component is mainly governed by delayed emission, which is present in both the exciton and trion state. The absence of a fine structure in trions clarifies the vanishing role of the dark exciton state for the long decay component. Our findings are essential for the development of a complete photophysical model that captures all observed features of fluorescence variations in colloidal nanocrystals.

Bright Luminous and Stable CsPbBr3 @PS Microspheres Prepared via Facile Anti-solvent Method using CTAB as Double Modifier.

The past decade has witnessed the increasing interest in cesium lead halide perovskite quantum dots (PQDs) for their excellent optical properties with higher photoluminescence efficiency and tunable emission wavelengths widely applied in white LED, photovoltaic devices, etc. Here we report the preparation of CsPbBr3 PQDs by a facile anti-solvent method using conventional quaternary ammonium bromide (CTAB) as a double modifier-both proper alkyl group protection and bromine source donator. The as-formed PQDs are well-monodispersed cubes with a size of 10-15 nm and high photoluminescence quantum yield (PLQY) of up to 43 %. To enhance the stability of PQDs, CsPbBr3 @PS microspheres were formed by electrospraying process. The microspheres not only show excellent luminous properties, but exhibit much higher stability against air and UV light irradiation due to the super hydrophobic property of polystyrene.

Surface Termination of CsPbBr3 Perovskite Quantum Dots Determined by Solid-State NMR Spectroscopy.

Cesium lead halide perovskite quantum dots (QDs) have gained significant attention as next-generation optoelectronic materials; however, their properties are highly dependent on their surface chemistry. The surfaces of cuboidal CsPbBr3 QDs have been intensively studied by both theoretical and experimental techniques, but fundamental questions still remain about the atomic termination of the QDs. The binding sites and modes of ligands at the surface remain unproven. Herein, we demonstrate that solid-state NMR spectroscopy allows the unambiguous assignment of organic surface ligands via 1H, 13C, and 31P NMR. Surface-selective 133Cs solid-state NMR spectra show the presence of an additional 133Cs NMR signal with a unique chemical shift that is attributed to Cs atoms terminating the surface of the particle and which are likely coordinated by carboxylate ligands. Dipolar dephasing curves that report on the distance between the surface ammonium ligands and Cs and Pb were recorded using double resonance 1H{133Cs} RESPDOR and 1H{207Pb} S-REDOR experiments. Model QD surface slabs with different possible surface terminations were generated from the CsPbBr3 crystal structure, and theoretical dipolar dephasing curves considering all possible 1H-133Cs/207Pb spin pairs were then calculated. Comparison of the calculated and experimental dephasing curves indicates the particles are CsBr terminated (not PbBr2 terminated) with alkylammonium ligands substituting into some surface Cs sites, consistent with the surface-selective 133Cs NMR experiments. These results highlight the utility of high-resolution solid-state NMR spectroscopy for studying ligand binding and the surface structure of nanomaterials.