Cesium Lead Halide Perovskite Nanocrystals Research Articles

Rapid synthesis of cesium lead halide perovskite nanocrystals by l-lysine assisted solid-phase reaction at room temperature.

Nowadays, there are many ways to obtain cesium lead halide perovskite nanocrystals. In addition to the synthesis methods carried out in solution, the solid-phase synthesis was reported involving grinding and milling. In this paper, we synthesized luminescent CsPbBr3/Cs4PbBr6 perovskite nanocrystals (PNCs) by three solid-phase synthesis methods (grinding, knocking, stirring) using l-lysine as a ligand. This is the first attempt to use an amino acid for assisting the solid phase synthesis of perovskite and to study the difference in the products obtained by the three solid phase synthesis methods. The results show that the productivity of the solid-phase synthesis methods can be greatly improved by adding l-lysine and the perovskites obtained by the methods are more resistant to water due to the addition of l-lysine. The simplicity of the synthesis process expanded the use of solid-phase synthesis to obtain more perovskites and provided potential applications of perovskite in analytical detection and sensing in aqueous solution.

Chemical analysis of cesium lead-halide perovskite nanocrystals by total-reflection X-ray fluorescence spectroscopy

Cesiumlead-halide perovskite nanocrystals are an emerging class of materials which potentially have different applications due to the several physical properties they exhibit. These properties are strongly dependent on the elemental composition of the nanocrystals and, to date, only few methods are available for their chemical analysis, such as scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX). The present work aims at establishing a new, fast and simple method for the elemental analysis of cesium lead-halide perovskite nanocrystals exploiting total-reflection x-ray fluorescence (TXRF) spectroscopy. The method was validated using a synthetized set of samples and comparing the TXRF results with SEM-EDX data. The sample preparation consisted in suspending the perovskites in 2.0 ml of hexane and sampling 10 μl of the suspension for deposition on a preheated quartz carrier. The element recovery ranged between 82% and 118% for mixed-halide perovskites, while for single halide perovskites it improved to 86%–105%. The present method can be implemented and used also for the elemental characterization of other types of perovskite nanocrystals.

Facile, low-cost, and large-scale synthesis of CsPbBr3 nanorods at room-temperature with 86 % photoluminescence quantum yield

All inorganic cesium lead halide perovskite nanocrystals have attracted widespread attention due to their excellent optical properties. However, large-scale synthesis of high photoluminescence quantum yield (PLQY) CsPbBr3 nanorods (NRs) is still challenging. Herein, we report a facile, low-cost and large-scale synthesis of CsPbBr3 NRs with 86 % PLQY at room temperature, in which the employment of acetic acid as precursor solvent promoted the concentrations of Cs+ and Pb2+ in the precursor solution and dominated the formation of CsPbBr3 NRs. The synthesized CsPbBr3 NRs with an average width of around 8 nm and average lengths of 18–30 nm have an excellent narrow-band (FWHM = 17 nm) green emission peaked at 517 nm.

Tracking the Fluorescence Lifetimes of Cesium Lead Halide Perovskite Nanocrystals During Their Synthesis Using a Fully Automated Optofluidic Platform

Semiconductive metal halide perovskites have opened exciting opportunities in a range of optoelectronic applications including solar cells, photodetectors, lasers, and light emitting devices. Recently, all-inorganic cesium lead halide (CsPbX3; X = Cl, Br, I) nanocrystals have become attractive light sources due to their high photoluminescence quantum yields, narrow emission linewidths, and emission color tunable over the entire visible region. Their radiative rates are higher (i.e., luminescence lifetimes shorter) than those of more conventional quantum dots, making perovskite NCs brighter emitters, highly attractive as both classical and quantum light sources. Multiple factors—primarily synthesis parameters and postsynthetic experience—govern the observed radiative lifetime and other optical characteristics. High-throughput experimentation in microfluidic platforms equipped with in-line optical characterization had proven to be highly instrumental for rapid and accurate assessment of optical properties, mainly in a steady-state mode. Thus far, in-line measurement of the radiative lifetimes and hence the proper use of high-throughput experimentation for tailored engineering of radiative rates have been elusive. Herein, we showcase a fully automated optofluidic platform that integrates time-correlated single photon counting measurements in droplet-based flow for the rigorous extraction of fluorescence lifetimes of CsPbX3 nanocrystals. The sensitivity of the experimental setup allows for measurements at a single-droplet level. Such concurrent time-resolved photoluminescence allows mapping the parametric space in a time-efficient manner (∼1000 lifetime measurements in 5 h of operation) and with high reagent economy (200 nL reaction volume per measurement). We elucidated the effects of composition and ratios of judiciously chosen reagents, as well as temperature on the fluorescence lifetimes (5–42 ns). Specifically, the average lifetime as well as the emission spectra of all halide compositions tested was strongly dependent on Pb-to-Cs variations. Accordingly a correlation between the steady-state luminescence amplitude and fluorescence lifetimes was established, thus providing a simple method to differentiate between the photoluminescence quantum yields, concentration effects, and effects due to the nonradiative recombination at the surface traps. Such a microfluidic tool will aid in analyzing the physicochemical and photophysical properties of diverse perovskite nanocrystals and other luminescent materials produced in the liquid-state synthesis.

In Situ Observation of Emission Behavior during Anion-Exchange Reaction of a Cesium Lead Halide Perovskite Nanocrystal at the Single-Nanocrystal Level.

Postsynthesis anion-exchange reaction of cesium lead halide (CsPbX3; X = Cl, Br, and I) perovskite nanocrystals (NCs) has emerged as a unique strategy to control band gap. Recently, the partially anion-exchanged CsPb(Br/I)3 NC was reported to form an inhomogeneously alloyed heterostructure, which could possibly form some emission sites depending on the halide composition in the single NC. In this work, we observed the in situ emission behavior of single CsPb(Br/I)3 NCs during the anion-exchange reaction. Photon-correlation measurements of the single NCs revealed that the mixed halide CsPb(Br/I)3 NC exhibited single-photon emission. Even when irradiated with an intense excitation laser, the single NC exhibited single-photon emission with a photoluminescence spectrum of a single peak. These results suggested that the heterohalide compositions of the CsPb(Br/I)3 NC do not form any emission sites with different band gap energies; instead, the NC forms emission sites with uniform band gap energy as a whole NC via quantum confinement.

Facile and rapid synthesis of high performance perovskite nanocrystals CsPb(X/Br)3 (X= Cl, I) at room temperature

All-inorganic cesium lead halide perovskite nanocrystals (NCs) are promising photoelectric materials for their high photoluminescence quantum yield (PLQY), narrow emission width and tunable optical band gap. Traditionally, the hot injection (HI) method has been utilized to prepare perovskite NCs. However, the HI method requires high temperature, protection under inert gas and other harsh synthetic conditions, which severely hinders large-scale production of these NCs. Herein, we directly synthesized CsPbBr3 perovskite NCs by a modified LARP (ligand-assisted re-precipitation) approach, and then conducted a specific anion exchange reaction with inexpensive, readily available, non-toxic, and non-polluting KX (X = Cl, I) salts aqueous solution to obtain various compositions of CsPbX3 perovskite NCs at room temperature (RT). The obtained RT-NCs have high PLQY and outstanding stability, and their photoluminescence can be precisely regulated across the whole visible region (419–670 nm). The use of inorganic salts for the ion exchange provides an efficient method for the design of various halogenated perovskite NCs and their large-scale synthesis at RT.

Generation of cesium lead halide perovskite nanocrystals via a serially-integrated microreactor system: Sequential anion exchange reaction

Inorganic perovskite nanocrystals (NCs) of cesium lead mixed halides (CsPb(X/Y)3, X = Br, Y = Cl and I) are promising optical materials for developing the high-performance photonic devices. Traditionally, anion-exchange reaction in perovskite halide NCs provides a simple substitutional way to tune the composition and emitting color with good luminescence properties in the human eye detectable visible spectral regions. However, prior synthetic procedures of perovskite NCs have employed conventional flask-based reactions which limit the fine control of perovskite NCs because of extremely fast anion-exchange kinetics. To overcome such problems, we demonstrate a droplet-based microfluidic system with simple, fast, and high-throughput parametric screening for the synthesis of perovskite NCs. By using the customized microfluidic operational system consisting of serially integrated two microfluidic reactors and heating block, we have successfully synthesized CsPbX3 perovskite NCs. In addition, we can finely control the anion-exchange reaction which can generate the formation of CsPb(X/Y)3 perovskite NCs with a wide range of visible spectrum (410–630 nm). Ultimately, we have established their potential applications in the development of solid-state lighting-based flexible display systems.

Mixed-Solvent Polarity-Assisted Phase Transition of Cesium Lead Halide Perovskite Nanocrystals with Improved Stability at Room Temperature.

Cesium lead halide perovskite nanocrystals (NCs) have attracted enormous interest in light-emitting diode, photodetector and low-threshold lasing application in terms of their unique optical and electrical performance. However, little attention has been paid to other structures associated with CsPbBr3, such as CsPb2Br5. Herein, we realize a facile method to prepare dual-phase NCs with improved stability against polar solvents by replacing conventional oleylamine with cetyltrimethyl ammonium bromide (CTAB) in the reprecipitation process. The growth of NCs can be regulated with different ratios of toluene and ethanol depending on solvent polarity, which not only obtains NCs with different sizes and morphologies, but also controls phase transition between orthorhombic CsPbBr3 and tetragonal CsPb2Br5. The photoluminescence (PL) and defect density calculated exhibit considerable solvent polarity dependence, which is ascribed to solvent polarity affecting the ability of CTAB to passivate surface defects and improve stoichiometry in the system. This new synthetic method of perovskite material will be helpful for further studies in the field of lighting and detectors.

Ligand-Mediated Release of Halides for Color Tuning of Perovskite Nanocrystals with Enhanced Stability.

The rich chemistry of metal halide perovskites has enabled various methods of band structure control and surface passivation. Here we report a highly facile and efficient post-treatment approach for precise color tuning of cesium lead halide perovskite nanocrystals (NCs) with enhanced stability. By utilizing a special multifunctional organic ligand, triphenyl(9-phenyl-9H-carbazol-3-yl)phosphonium bromide (TPP-Carz), carbon-halide bond cleavage can be achieved to release halide ions from halogenated solvents in a controlled manner for color tuning of perovskite NCs via ion exchange. Besides controlled release of halide ions for anion exchange, TPP-Carz can effectively passivate the surfaces of perovskite NCs simultaneously. As a result, perovskite NCs prepared by this post-treatment method with tunable colors over the entire visible spectrum have shown significantly improved luminescence and stability in comparison to the ones prepared using reactive anion precursors without surface passivation by TPP-Carz.

Setting an Upper Bound to the Biexciton Binding Energy in CsPbBr3 Perovskite Nanocrystals.

Cesium lead halide perovskite nanocrystals are promising emissive materials for a variety of optoelectronic applications. To fully realize the potential of these materials, we must understand the energetics and dynamics of multiexciton states which are populated under device relevant excitation conditions. We utilized time-resolved and spectrally-resolved photoluminescence studies to investigate the biexciton binding energy as well as a red-shifted emission feature previously reported under high-flux excitation conditions. We determine that this red-shifted emission feature can be ascribed to sample sintering induced by air-exposure and high-flux irradiation. Furthermore, we determine that the biexciton binding energy at room temperature is at most ±20 meV, providing a key insight toward understanding many-body interactions in the lead halide perovskite lattice.

Multiplexed patterning of cesium lead halide perovskite nanocrystals by additive jet printing for efficient white light generation

Inorganic perovskite nanocrystals (PNCs) offer the ability to precisely but also flexibly control the peak emission wavelength while also possessing narrow-band emission spectra and high quantum yields. Owing to these features, PNCs have been already employed as color converters on LEDs. Nevertheless, the anion exchange reactions that prevent the blending of perovskites of different colors remain as an important bottleneck. As a remedy to this issue, here we employ additive jet printing to form separated stripes of these nanocrystals. Within this framework, we first present the synthesis of CsPbBr3 and CsPbBrxI3−x nanocrystals spanning the whole visible regime and optimize the cleaning procedure to obtain PNCs possessing photoluminescence quantum yields as high as 91% and emission linewidths as narrow as 15 nm, making them suitable for high quality white light generation. Next, we employ electrohydrodynamic jet printing to form closely spaced stripes of PNCs of various colors and integrated these films with a blue LED to create a white LED. Our proof-of-concept LED achieves high photometric performance as it possesses a color rendering index of 91.3, luminous efficacy of optical radiation >300 lm/Wopt, and correlated color temperature of ca. 7000 K. We believe that additive jet printing technique will pave the way for a ubiquitous use of these PNCs in light-emitting devices in the near future.

Ultra-high stability of cesium lead halide nanocrystals synthesized by a simple one-pot method

Three-dimensional (3D) all-inorganic cesium lead halide perovskite nanocrystals (NCs) have showed significant potential in optoelectronic applications due to their unparalleled optical properties, but it still remains problems in applications, especially their poor stability. Recently, zero-dimensional (0D) all-inorganic cesium lead halide perovskite NCs have been attracted much attention due to the high stability. In order to achieve excellent luminescent performance of perovskite NCs with high stability, it has been proposed a nanostructure of Cs4PbBr6 NCs with embedded CsPbBr3 (CsPbBr3@Cs4PbBr6). In this paper, we developed a simple one-pot synthesis method for CsPbBr3@Cs4PbBr6 NCs, which was processed in octane with oil bath under air ambient and simplify the tedious process of purification. By this method, it was obtained nearly uniform (46 ± 2 nm) CsPbBr3@Cs4PbBr6 NCs with high photoluminescence quantum yield (PLQY, 85.3%, in solution). Moreover, the synthesized CsPbBr3@Cs4PbBr6 NCs powder exhibited remarkable durability with hour-scale photostability, thermostability at 80 °C and long-term storage over 180 days in air. This simplified synthesis method would open a new avenue for simply enhancing the stability of perovskite nanocrystals, and pave a huge potential path for mass production of perovskite nanocrystals.

Oxalic Acid Enabled Emission Enhancement and Continuous Extraction of Chloride from Cesium Lead Chloride/Bromide Perovskite Nanocrystals.

All-inorganic cesium lead halide perovskite nanocrystals (NCs) have demonstrated excellent optical properties and an encouraging potential for optoelectronic applications; however, mixed-halide perovskites, especially CsPb(Cl/Br)3 NCs, still show lower photoluminescence quantum yields (PL QY) than the corresponding single-halide materials. Herein, anhydrous oxalic acid is used to post-treat CsPb(Cl/Br)3 NCs in order to initially remove surface defects and halide vacancies, and thus, to improve their PL QY from 11% to 89% for the emission of 451 nm. Furthermore, due to the continuous chelating reaction with the oxalate ion, chloride anions from the mixed-halide CsPb(Cl/Br)3 perovskite NCs could be extracted, and green emitting CsPbBr3 NCs with PL QY of 85% at 511 nm emission are obtained. Besides being useful to improve the emission of CsPb(Cl/Br)3 NCs, the oxalic acid treatment strategy introduced here provides a further tool to adjust the distribution of halide anions in mixed-halide perovskites without using any halide additives.

Aqueous Phase Exfoliating Quasi-2D CsPbBr3 Nanosheets with Ultrahigh Intrinsic Water Stability.

All-inorganic cesium lead halide perovskite nanocrystals (NCs) have emerged as attractive optoelectronic materials due to the excellent optical and electronic properties. However, their environmental stability, especially in the presence of water, is still a significant challenge for their further commercialization. Here, ultrahigh intrinsically water-stable all-inorganic quasi-2D CsPbBr3 nanosheets (NSs) via aqueous phase exfoliation method are reported. Compared to conventional perovskite NCs, these unique quasi-2D CsPbBr3 nanosheets present an outstanding long-term water stability with 87% photoluminescence (PL) intensity remaining after 168 h under water conditions. Moreover, the photoluminescence quantum yields (PLQY) of quasi-2D CsPbBr3 NSs is up to 82.3%, and these quasi-2D CsPbBr3 NSs also present good photostability of keeping 85% PL intensity after 2 h under 365 nm UV light. Evidently, such quasi-2D perovskite NSs will open up a new way to investigate the intrinsic stability of all-inorganic perovskites and further promote the commercial development of perovskite-based optoelectronic and photovoltaic devices.

Unusual Stability and Temperature-Dependent Properties of Highly Emissive CsPbBr3 Perovskite Nanocrystals Obtained from in Situ Crystallization in Poly(vinylidene difluoride).

All-inorganic cesium lead halide perovskite nanocrystals (CsPbX3, X = Cl, Br, or I) present broad applications in the field of optoelectronics due to their excellent photoluminescence (PL), narrow spectral bandwidth, and wide spectral tunability. However, their poor stability limits their practical application. In this work, we successfully use an in situ crystallization strategy for growing and cladding CsPbBr3 perovskite nanocrystals in poly(vinylidene difluoride) (PVDF). The CsPbBr3 nanocrystals in the as-fabricated CsPbBr3@PVDF composites have an average diameter of 16-18 nm and a strong PL emission (537 nm), with a photoluminescence quantum yield exceeding 30%. In addition, the fabricated CsPbBr3@PVDF composites present improved resistance to heat and water preserving with remarkable optical performance, owing to the effective protection of PVDF. Moreover, the CsPbBr3 nanocrystals generated in PVDF can withstand temperatures up to 170 °C and can be completely immersed in water for 60 days while still retaining high PL intensity, which facilitate the practical application of CsPbBr3 perovskite nanocrystals. These CsPbBr3@PVDF composite films with remarkable optical performances and superior anti-interference ability have broad application prospects in optoelectronics as well as good potential as temperature sensors in mechanical engineering.

Fabrication and microstructure of perovskite CsPbCl3 nanocrystallized chalcogenide glass‐ceramics

AbstractTransparent chalcogenide glass‐ceramics containing CsPbCl3 perovskite nanocrystals were prepared through an elaborated composition design of 80GeS2·5Ga2S3·15CsPbCl3. Large size distribution of CsPbCl3 nanocrystals is observed ranging from 10 to 200 nm. XRD, Raman spectra, and SEM techniques were employed to study the further microstructural evolution after thermal treatment. The precipitation of PbGeS3 and GeS2, together with CsPbCl3, was identified according to the XRD patterns and Raman spectra. This work is of guiding significance for future design of cesium lead halide perovskite nanocrystals in chalcogenide glass‐ceramics.

Exciton Fine Structure in Perovskite Nanocrystals.

The bright emission observed in cesium lead halide perovskite nanocrystals (NCs) has recently been explained in terms of a bright exciton ground state [ Becker et al. Nature 2018 , 553 , 189 - 193 ], a claim that would make these materials the first known examples in which the exciton ground state is not an optically forbidden dark exciton. This unprecedented claim has been the subject of intense experimental investigation that has so far failed to detect the dark ground-state exciton. Here, we review the effective-mass/electron-hole exchange theory for the exciton fine structure in cubic and tetragonal CsPbBr3 NCs. In our calculations, the crystal field and the short-range electron-hole exchange constant were calculated using density functional theory together with hybrid functionals and spin-orbit coupling. Corrections associated with long-range exchange and surface image charges were calculated using measured bulk effective mass and dielectric parameters. As expected, within the context of the exchange model, we find an optically inactive ground exciton level. However, in this model, the level order for the optically active excitons in tetragonal CsPbBr3 NCs is opposite to what has been observed experimentally. An alternate explanation for the observed bright exciton level order in CsPbBr3 NCs is offered in terms of the Rashba effect, which supports the existence of a bright ground-state exciton in these NCs. The size dependence of the exciton fine structure calculated for perovskite NCs shows that the bright-dark level inversion caused by the Rashba effect is suppressed by the enhanced electron-hole exchange interaction in small NCs.

High-Efficiency Violet-Emitting All-Inorganic Perovskite Nanocrystals Enabled by Alkaline-Earth Metal Passivation

Cesium lead halide perovskite nanocrystals (NCs) have emerged as promising luminescent materials for a range of applications. However, the creation of highly luminescent violet-emitting CsPbCl3 NCs mostly relies on doping of a limited number of small-sized metal ions or post-synthetic surface treatment of NCs. Alkaline-earth (AE) metals (e.g., Ca2+, Sr2+, and Ba2+) have been proposed to be able to substitute Pb2+ in halide perovskites, yet it remains incompletely understood whether AE metal ions can be incorporated into the perovskite lattice or can be merely situated at the surface. Here, we explore the possibility of using AE metal ions for the suppression of the formation of trap centers, which leads us to develop a one-pot synthetic passivation strategy to boost the violet-emitting efficiency of CsPbCl3 NCs through the creation of a Ca2+/Sr2+ involved passivation layer. The photoluminescence quantum yield of violet emission reaches 77.1% by incorporating an optimal amount of Ca2+. A wide range of opti...

From Nonluminescent to Blue-Emitting Cs4 PbBr6 Nanocrystals: Tailoring the Insulator Bandgap of 0D Perovskite through Sn Cation Doping.

All-inorganic cesium lead halide perovskite nanocrystals (NCs) with different dimensionalities have recently fascinated the research community due to their extraordinary optoelectronic performance such as tunable bandgaps over the entire visible spectral region. However, compared to well-developed 3D CsPbX3 perovskites (X = Cl, Br, and I), the bandgap tuning in 0D Cs4 PbX6 perovskite NCs remains an arduous task. Herein, a simple but valid strategy is proposed to tailor the insulator bandgap (≈3.96 eV) of Cs4 PbBr6 NCs to the blue spectral region by changing the local coordination environment of isolated [PbBr6 ]4- octahedra in the Cs4 PbBr6 crystal through Sn cation doping. Benefitting from the unique Pb2+ -poor and Br- -rich reaction environment, the Sn cation is successfully introduced into the Cs4 PbBr6 NCs, forming coexisting point defects comprising substitutional SnPb and interstitial Bri , thereby endowing these theoretically nonluminescent Cs4 PbBr6 NCs with an ultranarrow blue emission at ≈437 nm (full width at half maximum, ≈12 nm). By combining the experimental results with first-principles calculations, an unusual electronic dual-bandgap structure, comprising the newly emerged semiconducting bandgap of ≈2.87 eV and original insulator bandgap of ≈3.96 eV, is found to be the underlying fundamental reason for the ultranarrow blue emission.

Metal Doping/Alloying of Cesium Lead Halide Perovskite Nanocrystals and their Applications in Light‐Emitting Diodes with Enhanced Efficiency and Stability

AbstractMetal halide perovskite nanocrystals (NCs) have demonstrated great advances for light‐emitting diodes (LEDs) applications, owing to their excellent optical, electrical properties and cost‐effective solution‐processing potentials. Tremendous progress has been made in perovskite NCs‐based LEDs during the past several years, with the external quantum efficiency (EQE) boosted to over 20 %. Recently, metal doping/alloying strategy has been explored to finely tune the optoelectronic properties and enhance material stability of perovskite NCs, leading to further improved device efficiency and stability of the obtained perovskite NCs‐based LEDs. In this review, we summarize recent progress on the metal doping/alloying of perovskite NCs and their applications in LEDs. We focus on the effects of different metal doping strategies on the structural and optoelectronic properties of the perovskite NCs. In addition, several works on high‐performance LEDs based on metal doped/alloyed perovskite NCs with different light emission colours are highlighted. Finally, we present an outlook on employing metal doping/alloying strategies to further improve the device efficiency and stability of LEDs based on perovskite NCs.