Inorganic Lead Halide Perovskite Nanocrystals Research Articles

Ligand engineering for improving the stability and optical properties of CsPbI3 perovskite nanocrystals

Inorganic lead halide perovskite nanocrystals (NCs) have recently become one of the research topics for optoelectronic applications due to their excellent photophysical properties. Despite their notable thermal stability over organic-inorganic halide perovskites, CsPbI3 NCs suffer from the phase instability of α-CsPbI3 phase at room temperature and under ambient conditions. Here, the effects of 4-Hydroxybenzoic acid (4-HBA) as an additive to standard oleic acid – oleylamine pair on the stability and optical properties of CsPbI3 perovskite NCs are discussed. 4-HBA addition into perovskite NC systems causes a compressive strain on perovskite lattice, which leads to the formation of a mixed phase α- and γ-CsPbI3 phases while pristine perovskite has α-CsPbI3 phase. Time-dependent stability of the perovskite NCs was tested under an ethanol (EtOH) medium. After EtOH exposure of the perovskite NCs, CsPbI3 NCs transformed to non-perovskite phase in 1 h while 4-HBA added CsPbI3 NCs still have perovskite phase after 48 h. In addition to the improved optical properties of the perovskite NCs, 4-HBA addition remarkably improves CsPbI3 perovskite stability.

Continuous Nanomanufacturing of Inorganic Lead Halide Perovskite Nanocrystals with High-Concentration Precursors.

The microscale flow preparation scheme has been widely used in the preparation of inorganic perovskite nanocrystals (NCs). It is considered to be the most promising method for large-scale production. Recently, it has been suggested that increasing the precursor concentration can further improve efficiency, but there is still a lack of understanding of high-concentration synthesis. Here, we develop a microscale flow synthesis scheme using high-concentration precursors, and the typical concentration value in the reaction phase reaches 0.035 mol/L using cesium acetate. The CsPbBr3 NCs with sharp photoluminescence (PL) at 515.7 nm can be obtained, and their PL quantum yield after post-treatment exceeds 90%. The effect of the molar ratio of Pb/Cs (Rm), reaction time, reaction temperature, and excess ligands on this flow reaction is studied. Several new phenomena are observed in our experiment. At 120 °C, some Cs4PbBr6 NCs exist in addition to the usual CsPbBr3 nanoplatelets. Excess ligands lead to the formation of numerous Cs4PbBr6 NCs with a bright green PL, and these NCs will spontaneously transform into a nonemission form in the film. Moreover, mixed-halide CsPbBrxI3-x NCs and CsPbI3 NCs are also prepared in this scheme, and then they are used to obtain LEDs in a range of colors.

Are Inorganic Lead Halide Perovskite Nanocrystals Promising Scintillators?

Inspections based on ionizing radiation have spread into various areas including our daily lives, industries, and scientific investigations and now face increasing demands with the development of society. Commercial X-ray detectors are mostly based on an indirect operation model in which the scintillator transforms X-ray photons into visible light and bottom photodiodes convert them into images. Obviously, the performance of the scintillator determines the final imaging properties, and the pursuit of scintillators with superior properties and lower cost is ongoing. Recently, inorganic lead halide perovskite nanocrystals (PNCs) emerged as promising scintillators for X-ray imaging. Here, we make a detailed conclusion of the superiority of PNC scintillators and take a new look at their scintillation performances. Discrepancies are discussed and some suggestions are proposed. Finally, perspectives on future developments, advice to the field, and proposed solutions to the problems toward full device performance and practical applications are provided.

Air-sensitive amplified spontaneous emission in lecithin-capped CsPbBr3 nanocrystals thin films

Fully inorganic lead halide perovskite nanocrystals (NCs) are receiving great attention as active materials for photonic and optoelectronic devices. While the lack of long-term stability, due to their sensitivity to ambient air exposure, currently prevents their application to commercial devices, the presence of reversible environmental effects opens the way for possible applications of lead halide perovskites in resistive or optical sensors. In this work we investigate the Amplified Spontaneous Emission (ASE) properties and their dependence on the surrounding environment of lecithin-capped CsPbBr3 NCs thin films. We demonstrate low ASE threshold under nanosecond pumping, both in air and in vacuum, with emission intensity lower in air than in vacuum. We also show that the emission quenching induced by ambient air exposure, ascribed to moisture-induced surface solvation, is reversible and it is fully restored by a suited vacuum stint application. The ASE sensitivity is up to 6.5 larger than the spontaneous emission one, making lecithin-capped CsPbBr3 NCs thin films promising systems for the development of optical humidity sensors with high sensitivity.

Ultrahigh energy density solid state supercapacitor based on metal halide perovskite nanocrystal electrodes: Real-life applications

Inorganic lead halide perovskite nanocrystals have now become an emerging material for modern nanodevice applications. But, the huge toxicity of lead to the ecosystem has limited its applications in modern technology. In this view, a large organic cation-based metal halide perovskite may be considered the most efficient supercapacitor electrode material. Here, a new type and high molecular organic cations based low-dimensional metal halide perovskite (LDMHP) nanocrystals (NCs) are synthesized by a chemical process and their performances as supercapacitor electrode is tested. An excellent charge storage capacity and especially the Tin (Sn)-based perovskite NCs showed a very high specific capacitance and energy density of ~1536 Fg−1 and ~213 Whkg−1 at a current density of 2.0 Ag−1, respectively. The calculated variable parameter (b) value from cyclic voltammetry showed that the total capacity of the Sn-based perovskite NCs electrode is controlled by capacitor-like behaviour. The Sn NCs also found to have a very high DC dielectric constant at room temperature, possibly responsible for their superior supercapacitor performance. A solid-state supercapacitor based on synthesized NCs was used for real-life applications of supplying sufficient power to light emitting diodes (LEDs) for a long time.

Stable and highly luminescent CsPbX3 (X= Br, Br/Cl) perovskite quantum dot embedded into Zinc(II) imidazole-4,5-dicarboxylate metal organic framework as a luminescent probe for metal ion detection

All inorganic lead halide perovskite nanocrystals (PeNCs) also called quantum dots (QDs) have emerged as a unique class of luminescent materials suitable for lighting and display technology. Unfortunately, such QDs are prone to degradation in ambient conditions, which inhibits their practical applicability. In this approach, CsPbX3 (X = Br, Br/Cl) PeNC was synthesized via a facile surfactant free two step in-situ growth technique by confining PeNC into the pores of a Zn based metal organic framework (MOF). The MOF was synthesized using zinc nitrate as a metal source and 4, 5-imidazole di-carboxylic acid as a linker. The formation of the PeNC/MOF composite was confirmed by XRD, SEM, TEM, and XPS analysis. Energy transfer from the Zn-HIMDC MOF matrix to the CsPbBr3 PeNC has been detected which in turn enhances its optical properties. The resulting CsPbBr3@MOF composite showed a very narrow and intense emission with full width half maxima (FWHM) at 20.5 nm. The emission maxima of CsPbX3@MOF was blue shifted with the addition of smaller halide Cl−. Due to the incorporation into the MOF template, the PeNC/MOF composite exhibits remarkable stability against moisture, ultraviolet light, heat, and polar solvents. Further, its superior stability and processibility have been exemplified by using it as a fluorescent probe for metal ion sensing.

Photo-induced charge transfer in composition-tuned halide perovskite nanocrystals with quinone and its impact on conduction current

A facile interfacial charge transfer (CT) with a reduced inter-layer energy band regulates the charge transport mechanism in any optoelectronic device. The enhancement in semiconductor-based device performance often demands improved CT dynamics and collection of free carriers with reduced charge recombination. In this work, we present a detailed inspection of the photo-induced CT between inorganic lead halide perovskite nanocrystals (PNCs) with varied compositions and their consequence on the charge transport process. The superior CT rate in mixed halide CsPbBr2Cl PNCs with naphthoquinone (NPQ) is revealed when compared with the parent CsPbBr3 PNCs and its anion-exchanged counterpart CsPbCl3. The glimpses of hole transfer contribution along with electron transfer are detected for CsPbBr2Cl with superior CT efficiency. The enhanced conduction current after the insertion of NPQ into the PNCs with a reduced hysteresis suggests an improved charge transport in the fabricated device compared to the pristine PNCs. These findings can contribute to a better understanding of multiple ways of engineering optoelectronic devices to boost performance and efficiencies and the concurrent role of the CT process in the conduction mechanism.

51.2: Invited Paper: The inorganic lead halide perovskite nanocrystals： the materials control and stability approach

51.2: <i>Invited Paper:</i> The inorganic lead halide perovskite nanocrystals： the materials control and stability approach

Quantifying Photoinduced Polaronic Distortions in Inorganic Lead Halide Perovskite Nanocrystals.

The development of next-generation perovskite-based optoelectronic devices relies critically on the understanding of the interaction between charge carriers and the polar lattice in out-of-equilibrium conditions. While it has become increasingly evident for CsPbBr3 perovskites that the Pb–Br framework flexibility plays a key role in their light-activated functionality, the corresponding local structural rearrangement has not yet been unambiguously identified. In this work, we demonstrate that the photoinduced lattice changes in the system are due to a specific polaronic distortion, associated with the activation of a longitudinal optical phonon mode at 18 meV by electron–phonon coupling, and we quantify the associated structural changes with atomic-level precision. Key to this achievement is the combination of time-resolved and temperature-dependent studies at Br K and Pb L3 X-ray absorption edges with refined ab initio simulations, which fully account for the screened core-hole final state effects on the X-ray absorption spectra. From the temporal kinetics, we show that carrier recombination reversibly unlocks the structural deformation at both Br and Pb sites. The comparison with the temperature-dependent XAS results rules out thermal effects as the primary source of distortion of the Pb–Br bonding motif during photoexcitation. Our work provides a comprehensive description of the CsPbBr3 perovskites’ photophysics, offering novel insights on the light-induced response of the system and its exceptional optoelectronic properties.

Modular Zwitterion-Functionalized Poly(isopropyl methacrylate) Polymers for Hosting Luminescent Lead Halide Perovskite Nanocrystals

Inorganic lead halide perovskite nanocrystals (NCs) are an exciting class of luminescent materials with high defect tolerance and broad spectral tunability, but such NCs are vulnerable to degradati...

Design a novel multifunctional (CsPbBr3/Fe3O4)@MPSs@SiO2 magneto-optical microspheres for capturing circulating tumor cells

All inorganic lead halide perovskite nanocrystals with excellent photoelectric characteristics as one of attractive new photoelectric materials are capable to apply in a variety of optoelectronic devices, but their instability and toxicity strongly impedes biological application. Herein, a novel approach of combining physical loading with hydrolytic packaging was exploited to firstly implant CsPbBr3 nanocrystals (NCs) and Fe3O4 quantum dots (QDs) into the mesoporous polystyrene microspheres (MPSs), then a silica shell layer was further coated on it to form the stable, safe and non-toxic (CsPbBr3/Fe3O4)@MPSs@SiO2 magneto-optical microspheres. The double core-shells packaging way not only improves the stability of the magneto-optical microspheres, but also avoids direct contact between CsPbBr3 NCs and biological target such as circulating tumor cells (CTCs) to solve the problem of heavy metal Pb in such material system. These magneto-optical microspheres can capture CTCs from both breast cancer cells (MCF-7) and lung cancer patient's blood in a few minutes. This work created a simple, safe and one-step method to identify and capture CTCs, which opens a new chapter for the application of lead halide perovskite in the biological field.

Thermal and photo stability of all inorganic lead halide perovskite nanocrystals.

Inorganic lead halide perovskite (ILHP) nanocrystals (NCs) show great potential in solid state lighting and next generation display technology due to their excellent optical properties. However, almost all ILHP NCs are still facing the problem of unstable luminescence properties caused by heating and/or UV illumination. Further improving the thermal and photo stability of ILHP NCs has become the most urgent challenge for their practical application. This Perspective review specifically focuses on the thermal and photo stability of ILHP NCs, discusses and analyzes the factors that affect the thermal and photo stability of ILHP NCs from the perspective of surface ligands and structure composition, summarizes the current strategies to improve the thermal and photo stability of ILHP NCs, and presents the key challenges and perspectives on the research for the improvement of thermal and photo stability of ILHP NCs.

Surface modification for improving the photoredox activity of CsPbBr3 nanocrystals.

In recent years inorganic lead halide perovskite nanocrystals (PNCs) have been used in photocatalytic reactions. The surface chemistry of the PNCs can play an important role in the excited state interactions and efficient charge transfer with redox molecules. In this work, we explore the impact of CsPbBr3 nanocrystal surface modification on the excited state interactions with the electron acceptor benzoquinone (BQ) for three different ligand environments: as oleic acid/oleylamine (OA/OAm), oleic acid (OA)/trioctylphosphine (TOP), and oleic acid (OA)/oleylamine (OAm)/trioctylphosphine (TOP) ligands. Our finding concludes that amine-free PNCs (OA/TOP capped) exhibit the best excited state interactions with benzoquinone compared to the conventional oleylamine ligand environment. The photoinduced electron transfer (PET) rate constants were measured from PL-lifetime decay measurement. The amine-free PNCs show the highest PET which is 9 times higher than that of conventional ligand capped PNCs. These results highlight the impact of surface chemistry on the excited-state interactions of CsPbBr3 NCs and in photocatalytic applications. More importantly, this work concludes that amine-free PNCs maintain a redox-active surface with a high photoinduced electron transfer rate which makes them an ideal candidate for photocatalytic applications.

Luminescent and Robust Perovskite-Silicone Elastomers Prepared by Light Induced Thiol-Ene Reaction.

The preparation of a series of luminescent perovskite-silicone elastomer (PSE) composites by embedding inorganic lead halide perovskite nanocrystals (CsPbBr3 NCs) into networks constructed by trimethylolpropane tris(2-mercaptoacetate) and sulfone-containing silicone copolymers with vinyl side groups (PSMVS) is reported herein. The networks are obtained by an environmentally friendly thiol-ene cross-linking reaction under 30 W household LED light. The conducted analysis shows that the prepared PSEs display strong green fluorescence due to encapsulation of CsPbBr3 NCs, which constitute a luminescent center in sulfone-containing silicone networks. Using PSMVS as basic polymers instead of commercial polysiloxanes endows PSEs with enhanced mechanical strength and excellent luminescent stability at high temperatures. The PSEs show robust tensile stress and >650%elongation. Additionally, the construction of colorful ultraviolet light-emitting diodes (UV-LEDs) by an in situ cross-linking process is described.

Highly Stable and Efficient Lead Halide Perovskite Nanocrystals for Light-Emitting Diodes Displays

All inorganic lead halide perovskite nanocrystals (NCs), CsPbX3 (X=Cl, Br, I), have been attracting increasing attention because of their excellent optical properties, such as tunable emission wavelength, high photoluminescence quantum yield (PLQY), narrow full width at half maximum (fwhm), and high defect tolerance. Therefore, the NCs have great potential application in light-emitting diodes for display. However, the NCs suffer from poor stability due to the hydrolytic degradation and fluorescence quenching in the solid agglomerations state. To improve the photoluminescence (PL) stability of the NCs, the ammonium bromide, alkyl phosphate, microscale Cs4PbX6, and super hydrophobic porous organic polymers (SHOP) were used as frameworks to from the composites with NCs. Specially, the CsPbBr3-super hydrophobic polymers composites not only preserve a high PLQY (60%) and narrow band emission (fwhm~16nm) but also inherit the outstanding water-resistant property of SHOP to protect the NCs from hydrolytic degradation. The PLQY of the composites was maintained at 91% of the initial one after being immersed in water for 31 days. Even after being immersed in water for six months, the composites still retain bright green emission. A white light-emitting diode (WLEDs) device was prepared by combining green-emitting composites and red-emitting K2SiF6:Mn4+ phosphors with a blue LED chip. The device exhibits a high luminous efficiency of 50 lm/W and a wide color gamut (127% of the National Television System Committee and 95% Rec. 2020). This work provides an alternative approach to solve the challenging stability issue of perovskite QDs; therefore, it has a positive implication for their practical application in liquid crystal display backlights.

Polaron and Spin Dynamics in Organic–Inorganic Lead Halide Perovskite Nanocrystals

AbstractLong‐lived carrier population and spin‐based behavior in lead halide perovskite nanocrystals (NCs) are extremely interesting for implementing photovoltaic devices with efficiencies exceeding the Shockley–Queisser limit and quantum information processing, respectively. However, a comprehensive understanding of polaron‐mediated charge carrier interactions and an accurate description of the spin‐polarized states for spintronics are still lacking. Herein, the carrier and spin interactions are studied under controlled conditions in FAPbI3 and Cs0.01FA0.99Pb(Br0.11I0.89)3 NCs through ultrafast transient absorption (TA) spectroscopy. At early timescales, TA spectrum shows an asymmetric derivative feature originating from the hot carrier‐induced spectral redshift in FAPbI3 NCs (55 ± 3 meV) and Cs0.01FA0.99Pb(Br0.11I0.89)3 NCs (54 ± 2 meV) at the bandedges that stabilizes to 9 ± 1 and 11 ± 2 meV, respectively, at 1 ps due to the polaron formation. The kinetic analysis indicates that the polaron populations in FAPbI3 and Cs0.01FA0.99Pb(Br0.11I0.89)3 NCs decay with an average lifetime of 657 ± 34 and 532 ± 28 ps, respectively. The circular polarization‐resolved TA reveals that polaron formation can control spin relaxation in NCs, thus providing a powerful tool to explore the development of their prospective applications in spintronics.

High-Performance Perovskite Light-Emitting Diodes with Surface Passivation of CsPbBrxI3–x Nanocrystals via Antisolvent-Triggered Ion-Exchange

Inorganic lead halide perovskite nanocrystals (PeNCs) have intensively drawn the attention as efficient light emitting materials for optoelectronic applications due to fine optoelectronic properties with high photoluminescence quantum yield and easily tunable saturated emission color. However, the low stability of the red-emitting PeNCs have become an obstacle because of the uncontrollable iodine substitution from the PeNCs owing weak Pb-I bonding. In this work, we have demonstrated a ligand-mediated post-treatment (LMPT) method using halide ion-pair ligand, tridodecylmethyl ammonium iodide (TrDAI), for the air stable and high-quality red-emitting PeNCs. Through the LMPT method, the optoelectronic properties of red-emitting PeNCs are dramatically improved resulting in the PLQY of 88.7% at 637 ± 2 nm emission with increased carrier lifetime from 20.77 ns to 31.52 ns. We achieve highly efficient red perovskite light-emitting diodes exhibiting a maximum current efficiency of 7.69 cd A-1 and an external quantum efficiency of 6.36% at 637 ± 2 nm electroluminescence emission with a sharp full-width at half maximum of 31 nm.

Room Temperature In-Situ Synthesis of Inorganic Lead Halide Perovskite Nanocrystals Sol Using Ultraviolet Polymerized Acrylic Monomers as Solvent and Their Composites with High Stability

As a kind of promising optoelectrical material, all-inorganic perovskite nanocrystals CsPbX3 (X = Cl, Br, I) have attracted much attention, due to their excellent optoelectrical characteristics, in recent years. However, their synthesis approaches require rigorous conditions, including high temperature, eco-unfriendly solvent or complex post-synthesis process. Herein, to overcome these issues, we reported a novel facile room temperature in-situ strategy using ultraviolet polymerizable acrylic monomer as solvent to synthesis CsPbX3 nanocrystals without a complex post-synthesis process. In this strategy, adequate soluble precursors of Cs, Pb and Br and reaction terminating agent 3-aminopropyltriethoxysilane (APTES) were used. The obtained CsPbBr3 nanocrystals showed a high photoluminescence quantum yields (PLQY) of 87.5%. The corresponding polymer composites, by adding light initiator and oligomer under ultraviolet light radiation, performed excellent stability in light, air, moisture and high temperature. The reaction process and the effect of the reaction terminating agent have been investigated in detail. This strategy is a universal one for synthesizing CsPbX3 nanocrystals covering visible light range by introducing HCl and ZnI2.

Controllable synthesis of all inorganic lead halide perovskite nanocrystals and white light-emitting diodes based on CsPbBr3 nanocrystals

The colloidal cesium lead halide perovskite nanocrystals (NCs) have attracted much attention over the past five years as a promising class of material with potential application in wide-color-gamut backlight display because of their high photoluminescence quantum yield (PLQY) and narrow-band emission (full-width at half-maximum, FWHM < 35 nm). To controllably synthesize perovskite NCs, the effects of reaction temperature and reaction time on structure, morphology, particle size and photoluminescence (PL) properties of the NCs were systematically investigated inthis article. Based on these results, the formation kinetics of the perovskite NCs was analyzed and disclosed in further. Finally, a white light-emitting diode (WLED) was prepared by using synthesized CsPbBr3 NCs and K2SiF6:Mn4+ phosphors as the color converters. The WLED exhibits the bright white emission with a CIE chromaticity coordinate of (0.389, 0.376) and a wide color gamut of 123% of NTSC, indicating a potential application in the field of wide color gamut displays in the future.

Controllable Synthesis of All Inorganic Lead Halide Perovskite Nanocrystals with Various Appearances in Multiligand Reaction System.

All inorganic cesium lead halide (CsPbX3, X = Cl, Br, I) perovskite nanocrystals (PNCs) exhibit promising applications in light-emitting devices due to their excellent photophysical properties. Herein, we developed a low-cost and convenient method for the preparation of CsPbX3 PNCs in a multiligand-assisted reaction system where peanut oil is applied as a ligand source. The mixed-halide PNCs with tunable optical-band gap were prepared by mixing the single-halide perovskite solutions at room temperature. The resulting PNCs had good monodispersity, with dimensions of 8–10 nm, high photoluminescence quantum yield (96.9%), narrow emission widths (15–34 nm), and tunable emission wavelength (408–694 nm), covering the entire visible spectrum. Additionally, various morphologies of PNCs, such as nanospheres, nanocubes, and nanowires, were obtained by controlling reaction temperature and time, and the amount of oleamine with multiple ligands in peanut oil potentially playing a dominant role in the nucleation/growth processes of our PNCs. Finally, the resulting CsPbBr3 PNCs were employed to develop a white light-emitting diode (WLED), demonstrating the potential lighting applications for our method.