CsPbX3 Perovskite Nanocrystals Research Articles

Defect Passivation of Mn2+-Doped CsPbX3(X=Cl,Br) Perovskite Nanocrystals as Electrocatalyst for Overall Water Splitting.

Mn doping has been used to improve the physical chemistry of lead halide perovskite nanocrystals such as CsPbX3, where X is a halogen ion. In this paper, a two-phase method for Mn-doped CsPbX3 nanosheets (where X=Br, Cl), namely water-hexane system, is reported. Compared to conventional catalyst arrays, the band gap of CsPbBr3 nanocrystalline is easily tuned, the carrier diffusion distance is remote, the band edge position of the band structure is favorable for a wide range of electrocatalytic redox reactions, and the catalytic active site is maximally exposed, providing a larger electrolyte contact area. The porous hierarchical structure also accelerates the release of hydrogen bubbles. The results showed that the optimized Mn : CsPbBr3 catalyst exhibited excellent electrolytic performance of aquatic hydrogen in alkaline electrolyte (1 mol/L KOH). The overpotentials of the oxygen evolution reaction (OER) at the current densities of 10 and 100 mA cm-2 are only 114.4 and 505.4 mV, respectively, with a Tafel slope of 43 mV dec-1. At a current density of 10 mA cm-2, the excess potential required for the hydrogen evolution reaction (HER) is 158.6 mV and it exhibits excellent electrochemical stability. The Mn : CsPbBr3 nanocrystalline consists of two electrodes for hydrolysis of water, requiring only a voltage of 1.45 V. This provides implications for the optimization of electrocatalysts in alkaline electrolytes with the aim of developing next generation 2D electrocatalysts for overall water splitting.

Crystallization and luminescence properties of stable CsPbBr3 Nanocrystals in Li2B4O7 glass

All-inorganic CsPbX3 (X = Cl, Br, and I) perovskite nanocrystals (NCs), have achieved unprecedented advances in opto-electronic applications. However, issues such as poor stability and the volatility of halides in the preparation process continue to hinder their practical applications. Here, lithium tetraborate (Li2B4O7) was chosen as the glass matrix to prepare CsPbBr3 NCs glasses through traditional melting-quenching and heat treatment processes, effectively reducing the glass synthesis temperature to 940 °C. The heat treatment temperature and duration are examined. The Li2B4O7 glass matrix exhibits a uniform structure and high transmittance and CsPbBr3 NCs precipitated uniformly after heat treatment. Among these glasses, the sample heat-treated at 510 °C for 5 h exhibited an optimal photoluminescence quantum yield of 76.1 % and the narrowest full width at half maximum values of 24 nm. Its photoluminescence intensity maintained 96.6 % of its original value after multiple thermal cycles and thermal shocks, demonstrating the sample's robust thermal stability. Finally, by integrating the CsPbBr3 NCs glass sample with a blue chip in simple device packaging, a green light-emitting diode was successfully fabricated, featuring excellent luminescence stability and a color purity of up to 96.4 %, promising for applications in solid-state lighting and display technologies.

Surface Cation Cross‐Locking Enables Non‐Destructive “On‐Demand” Synthesis of Anion‐Exchanged CsPbX3 Perovskite Nanocrystals

AbstractPost‐synthetic halide anion exchange is considered a “double‐edged sword” for perovskite nanocrystals (PNCs), which offer unique access to color tunability while bringing about surface defects. Herein, a novel surface cation cross‐locking (SCCL) strategy is proposed to achieve the anion‐exchanged CsPbX3 PNCs (X is Cl, Br, I) with non‐destructive emissions. This is achieved using a dendritic ligand of Pentaerythritol tetrakis (3‐mercaptopropionate) (PETMP) as a surface cross‐locker, which can form the multiple coordination to the surface Pb cation of octahedral [PbX6]4− during the fast halide anion exchange via four end‐thiolates and four side‐carboxylates. As a result, the red‐ and blue‐emitting anion‐exchanged CsPbX3 PNCs exhibit high photoluminescence quantum yield (PLQY) values of >97%, close to the parent green‐emitting CsPbBr3 PNCs. Moreover, the “on‐demand” synthesis of anion‐exchanged CsPbX3 PNCs is also performed via autonomous robotic in‐flow experimentation. This work provides a new general post‐synthetic way for the full‐color CsPbX3 PNCs with compositions that are inaccessible via direct synthetic routes.

Dual Passivation Strategy for Highly Stable Blue-Luminescent CsPbBr3 Nanoplatelets.

Blue-emitting colloidal CsPbX3 (X = Br, Cl, or I) perovskite nanocrystals have emerged as one of the most fascinating materials for optoelectronic applications. However, their applicability is hindered by poor stability and a low photoluminescence efficiency. Herein, highly stable CsPbBr3 nanoplatelets exhibiting intense blue luminescence are fabricated by employing a strategy in which the morphology is regulated and the surface is subjected to dual passivation through the incorporation of zirconium acetylacetonate [Zr(acac)4]. The passivated CsPbBr3 nanocrystals exhibit adjustable light emission from green to dark blue and a controllable morphology from nanocubes (NCs) to nanoplatelets (NPLs) and nanorods accomplished by varying the content of Zr(acac)4. The optimized NPLs are characterized by a bright blue emission with a central wavelength of 459 nm and a high photoluminescence quantum yield of 90%. The addition of Zr(acac)4 in the synthesis of CsPbBr3 induces oriented growth with a two-dimensional morphology. The Zr(acac)4 can repair the surface defects of the nanocrystal surface, and the surface is also capped with the Zr(OH)4 cluster layer. Therefore, the passivated blue-emitting NPLs exhibit outstanding stability compared to that of pristine NPLs during long-term storage and exposure to light. This work provides a novel strategy for fabricating highly stable PNCs with deep-blue emission and widens their potential applications in blue-emitting optoelectronic devices.

One-step synthesis of highly fluorescent perovskite nanocrystals in antisolvent for bioimaging

All inorganic perovskite nanocrystals (CsPbX3 NCs) have excellent optical properties with high quantum yield, size tunable absorption and emission spectra which makes them popular for a wide variety of applications. All the commonly used synthesis techniques, such as hot injection and ligand assisted reprecipitation method (LARP), use ‘good’ solvent such as dimethyl formamide, dimethyl sulfoxide or octadecene to dissolve the precursor salts. The CsPbX3 NCs formation is triggered either by rapid injection of the dissolved precursor salt in hot mixture (hot injection) or by adding a ‘good’ solvent into a ‘poor’ solvent (LARP) that induces crystallization. Here, we present an alternative synthesis of CsPbX3 perovskite nanocrystals in an antisolvent system, instead of a ‘good’ solvent. Crystallization in the antisolvent is induced by adding a trace amount of water, leading to the formation of highly bright CsPbX3 nanocrystals. This method resulted in a maximum photoluminescent quantum yield of ∼91%. Furthermore, these CsPbBr3 NCs can be modified to create core–shell structures with polymers such as silica, in the same pot. Encapsulating the NCs within a protective silica shell resulted in vastly superior water stability compared to the bare NCs. The silica coated CsPbBr3 NCs showed strong fluorescence in water were used to label breast cancer cells, thereby demonstrating its potential as an optical contrast agent for advanced bioimaging applications. Overall, this synthesis approach requires minimal steps and time, and can be carried out in an ambient atmosphere, thereby increasing its versatility and practicality, which is particularly attractive in low-resource settings.

Highly luminescent polyfluorene-based composite with CsPbX3 perovskite nanocrystals for light-emitting devices

The rapid development of thin-film light emitting devices (LED) technologies has recently been associated with the superior optoelectronic properties of luminescent materials based on lead halide perovskite nanocrystals (NCs) due to their narrow emission line with high color purity. However, the large surface area of NCs leads to the need to use solvating ligands to prevent their agglomeration, which limits their use in optoelectronics. Here we develop a class of modular polyfluorene (PF) copolymer with 4-hydroxyphenyl-, diethylamino- and diethoxyphosphoryl- groups designed to stabilize perovskite NCs. We show that as-synthesized CsPbBr3 NCs can easily be mixed with custom-designed PFs resulting in polymer/NCs composite that shows efficient Förster energy transfer (FRET) from PF to NC with green photoluminescence (PL). We also found that the NCs composite studied here can be used as an effective emissive layer in LED due to the strong interaction between polymer host and perovskite NCs providing an efficient charge transfer from the PF matrice to the NC emitter. The fabricated LED show excellent performance with a highest current efficiency of ∼25.2 cd A–1. Our approach provides a low-cost and efficient way for light-emitting optoelectronic applications based on perovskite NCs.

Retarding anion exchanges in lead halide perovskite nanocrystals by ligand immobilization.

CsPbX3 (X = Cl-, Br-, I-) perovskite nanocrystals (PNCs) undergo rapid anion exchange, allowing easy bandgap tuning across the entire visible range. However, despite being highly luminescent, the same facile anion exchange process poses significant challenges for their use in tandem optoelectronic devices and white light-emitting diodes (WLEDs). This anion exchange occurs primarily due to the dynamic nature of loosely bound oleylamine ligands on the surface of the PNCs. The mobility of these loosely bound ligands is a key factor in the rapid anion exchange, suggesting that immobilizing these ligands could effectively inhibit the process. To address this, we report a unique approach involving the immobilization of ligands through crosslinking. By crosslinking the ligands on the surface of the PNCs, we can significantly retard the anion exchange process. Our research demonstrates that the anion exchange process can be effectively slowed down by carefully controlling the extent of ligand immobilization. Furthermore, our findings provide the reaction kinetics of anion exchange retardation in CsPbX3 NCs through ligand immobilization by plasma treatment.

Direct synthesis of CsPbX3 perovskite nanocrystal assemblies.

Inorganic CsPbX3 (X = Cl, Br, I) perovskite nanocrystals (NCs) possess many advantageous optoelectronic properties, making them an attractive candidate for light emitting diodes, lasers, or photodetector applications. Such perovskite NCs can form extended assemblies that further modify their bandgap and emission wavelength. In this article, a facile direct synthesis of CsPbX3 NC assemblies that are 1 μm in size and are composed of 10 nm-sized NC building blocks is reported. The direct synthesis of these assemblies with a conventional hot-injection method of the NCs is achieved through the judicious selection of the solvent, ligands, and reaction stoichiometry. Only under selective reaction conditions where the surface ligand environment is tuned to enhance the hydrophobic interactions between ligand chains of neighbouring NCs is self-assembly achieved. These assemblies possess narrow and red-shifted photoluminescence compared to their isolated NC counterparts, which further expands the colour gamut that can be rendered from inorganic perovskites. This is demonstrated through simple down-converting light emitters.

Exploring CsPbX3 (X = Cl, Br, I) Perovskite Nanocrystals in Amorphous Oxide Glasses: Innovations in Fabrication and Applications.

Metal halide perovskites with excellent optical and electronic properties have become a trending material in the current research. However, their limited stability under ambient conditions degrades quality and threatens their potential commercialization as optoelectronic devices. Various approaches are adopted to improve the stability of perovskite nanocrystals (PeNC) while maintaining their advantageous optical properties, particularly strong luminescence. Among different possible improvement strategies, encapsulation of PeNCs within the amorphous glass matrices of inorganic oxides has drawn widespread attention because it ensures high resistance against chemical corrosion and high temperature, thus enhancing their chemical, thermal, and mechanical stability with improved light-emission characteristics. In this article, two types of materials, namely all-inorganic metal halide PeNCs and amorphous oxide glasses are briefly introduced, and then the methods are reviewed to fabricate and improve the quality of PeNC@glass composites. These methods are classified into three universal categories: compositional modification, structural modification, and dual encapsulation. In the final part of this review paper, examples of applications of PeNCs@glass composites in light-emitting devices and displays, data storage and anti-counterfeiting, lasing, photodetectors and X-ray detectors, photocatalysis, optical filters, solar concentrators, and batteries are provided.

Space‐confined growth of CsPbBr3 nanocrystals in mesoporous KIT‐6 and application in LEDs

AbstractAll‐inorganic CsPbX3 (X = Cl, Br, and I) perovskite nanocrystals (NCs) have great application prospects in many fields due to their excellent photoelectric properties. However, CsPbX3 NCs are extremely sensitive to water, heat, light, and oxygen, which leads to dramatic photoluminescence quenching and seriously restricts their future commercial applications. Herein, a novel, simple one‐step solution strategy for synthesizing high‐quality CsPbBr3 NCs was reported. By the combination of the hot‐injection process with the mesoporous template confinement effect of the KIT‐6 matrix, the space‐confined growth of NCs was precisely achieved. The CsPbBr3 NCs encapsulated by KIT‐6 (CsPbBr3@KIT‐6 composite) exhibited a uniform size, a high photoluminescence quantum yield (PLQY) of up to 82%, and a narrow full width at half‐maximum (FWHM) of 24 nm. Most importantly, CsPbBr3@KIT‐6 powder composites had dramatically enhanced light, thermal and water stability in comparison with colloidal CsPbBr3 NCs due to the dual protection of organic ligands and matrix templates. Ultimately, a white light‐emitting diode (LED) device was successfully fabricated by encapsulating a mixture of green‐emitting CsPbBr3@KIT‐6 composite and red‐emitting K2SiF6:Mn4+ phosphor onto a blue‐emitting InGaN LED chip. A color coordinate of (0.327, 0.337) and a wide color gamut of 128% NTSC well demonstrate their potential applications in lighting and display.

A soft-chemistry route to prepare halide perovskite nanocrystals with tunable emission and high optical performance

AbstractCesium lead halide perovskites constitute a benchmark family of inorganic perovskites for high performance optoelectronic devices. Hot injection is by far the most extended procedure to fabricate CsPbX3 (X: Cl, Br, and/or I) perovskite nanocrystals (PNCs) of high quality. However, the tedious N2-vacuum cycles and fast heating/cooling steps hinder the large-scale production of these materials. This work presents a fast one-step methodology to fabricate small CsPb(ClxBr1-x)3 nanocrystals with good control of the particle size and shape by using a Soft Chemistry strategy (ligand-mediated controlled growth) and microwave heating. We demonstrate that the procedure can be extended to different mixed halide perovskites, thus providing a fine tuning of the chemical composition and consequently, tunable photoluminescence (PL) emission from 522 nm for pure CsPbBr3 to 477 nm for CsPb(Cl0.4Br0.6)3, high photoluminescence quantum yield (PLQY) up to ~86% (for CsPbBr3) and narrow PL full width at half maximum ~18–26 nm. In addition, the protocol was designed in such a way that the chemistry involved in the crystal nucleation and growth of perovskites is as close as possible to that of the hot injection process, which is mechanistically well-understood, to facilitate their adoption by the perovskite research community. Graphical Abstract

Boosting the Photoluminescence Quantum Yield and Stability of Lead-Free CsEuCl3 Nanocrystals via Ni2+ Doping.

Colloidal CsPbX3 (X = Br, Cl, or I) perovskite nanocrystals (PNCs) have emerged as low-cost, high-performance light-emitting materials, whereas the toxicity of lead limits their applications. Europium halide perovskites offer promising alternatives to lead-based perovskites due to their narrow spectral width and high monochromaticity. Nonetheless, the photoluminescence quantum yields (PLQYs) of CsEuCl3 PNCs have been very low (∼2%). Herein, Ni2+-doped CsEuCl3 PNCs have been first reported, exhibiting bright blue emission centered at 430.6 ± 0.6 nm with a full width at half-maximum of 23.5 ± 0.3 nm and a PLQY of 19.7 ± 0.4%. To the best of our knowledge, this is the highest PLQY value reported for CsEuCl3 PNCs so far, an order of magnitude higher than in previous work. DFT calculations demonstrate that Ni2+ enhances PLQY by concurrently increasing the oscillator strength and removing Eu3+ which hinders the photorecombination process. B-site doping offers a promising approach to enhance the performance of lanthanide-based lead-free PNCs.

Highly Stable CsPbBr3 Perovskite Nanocrystals Encapsulated in Metal–Organic Frameworks for White Light-Emitting Diodes

CsPbX3 (X = Cl, Br, I) perovskite nanocrystals (NCs) have shown great potential in numerous applications including wide color gamut display and lighting. Despite the wonderful luminescence properties, the inherent instability of these NCs hinders their use in practical situations. Herein, we report a facile aqueous-based, ligand-free method to synthesize highly stable CsPbX3 NCs using ZIF-62, a metal–organic framework, as an encapsulation matrix which effectively isolates CsPbX3 from the surrounding. We discovered that the slightly alkaline nature of ZIF-62 facilitates the reaction between water and PbBr2 to form PbBr(OH), which not only passivates the surface defects of the CsPbBr3 NCs but also prevents the perovskite from decomposing or oxidizing at high temperature. Sintering of ZIF-62 can therefore be performed in air at ∼300 °C to completely seal the perovskite within the insulating matrix, resulting in CsPbBr3/ZIF-62 composites exhibiting high stability against polar solvents, heat, light, and ambient humidity. Notably, the composite can maintain its bright luminescence without noticeable degradation in water for more than 2 months. The narrow-band emission and stability of these composites led to the demonstration of white light-emitting diodes with excellent color stability. Without the need for organic solvents during NC synthesis and noble gas ambient during sintering, the strategy proposed here can potentially facilitate the cost-effective, large-scale synthesis of highly stable perovskites which show great promise in commercial applications.

Intense blue emission from one-pot synthesized quaternary CsZnxPb1-xBr3 perovskite quantum dots

Suitable ions incorporation into CsPbX3 perovskite nanocrystals can improve the luminescence efficiency, chemical stability, and more importantly modify the emission bands from semiconductor band gap change, for various applications. In this research, high content Zn2+ was introduced into CsPbBr3 quantum dots through a simple one-pot synthesis method. A new intense blue emission centered at 440 nm was observed from heavy Zn alloyed nanocrystals, for increased semiconductor band gap, along with green emission at 510 nm from CsPbBr3 quantum dots, when the ratio of ZnBr2/PbBr2 precursor was larger than unity. The appearance of Zn 3d peaks and the decreasing of bonding energy of Pb 4f peaks from X-ray photoelectron spectroscopy spectra indicated that Zn2+ ions were incorporated into CsPbBr3 quantum dots to form CsZnxPb1-xBr3 alloyed quantum dots. The elements quantitative analysis showed that partial Zn2+ ions in precursors were involved in the synthesis of the quantum dots, and the Zn alloyed perovskite nanocrystals could be described as CsPbBr3, CsZn0.43Pb0.57Br3, CsZn0.54Pb0.46Br3, CsZn0.68Pb0.32Br3 respectively when the ZnBr2/PbBr2 precursor ratios were 0:1, 1:1, 3:1 and 5:1. The X-ray diffraction patterns confirmed that the incorporation of small radius Zn2+ ions into crystals led to crystal shrinkage, instead of crystal phase change. The transmission electron microscope images of the nanocrystals showed cubic geometries and reduced average sizes from 23.3 nm to 17.6 nm with Zn2+ content increase, resulting in the blue shift of emission bands. The energy dispersive spectroscopy elemental mapping of nanocrystals also confirmed the incorporation of Zn2+ ions into the nanocrystals.

Anchoring palladium nanoparticles on CsPbBr3 perovskite nanocrystals for enhanced photocatalytic CO2 reduction

Recently, all-inorganic cesium lead halide (CsPbX3 (X = Cl, Br, and I) perovskite nanocrystals (NCs) have been extensively investigated for photocatalytic carbon dioxide (CO2) reduction reaction (CO2RR). However, because the pristine CsPbX3 NCs suffer from severe radiative recombination, it is imperative to elaborately design heterostructures to separate electron-hole pairs for achieving efficient CO2RR. Herein, palladium (Pd) nanoparticles (NPs) are anchored on CsPbBr3 NCs by a photo-assisted approach for the first time. The as-prepared CsPbBr3@Pd NCs not only build Schottky junctions at the CsPbBr3/Pd interfaces that promote the carrier separation and suppress the radiative recombination, but also exhibit lower energy barriers for photocatalytic CO2RR than pristine CsPbBr3 NCs according to the density functional theory calculations. The electron consumption rate reaches a striking peak of 46.2 µmol g−1 h−1 by using CsPbBr3@Pd NCs as photocatalysts for CO2RR, which is 4.8-fold of the counterpart of pristine CsPbBr3 NCs. This work not only presents a photo-assisted strategy for anchoring Pd NPs on CsPbBr3 NCs, but also demonstrates the great potential of using CsPbBr3@Pd NCs for photocatalytic CO2RR.

Tuning the luminescence of thin nanocrystalline CsPbBr-=SUB=-3-=/SUB=- perovskite films during the in situ anion exchange reaction

Inorganic perovskite CsPbX3 nanocrystals (PNCs), where X is a halide anion, are currently promising materials for a wide range of optoelectronic devices. One of the key tasks to be solved before they are used in practice is to obtain stable thin PNC films whose luminescence wavelength could be finely tuned. The chemical composition of CsPbX3 PNCs is the main parameter determining their band gap width and, hence, the position of their photoluminescence maximum. Variation of the PNC composition in the course of their synthesis or postsynthetic treatment in solution makes it possible to obtain CsPbBr(3-x)Ix and CsPbBr(3-y)Cly materials emitting in the entire visible spectral range. In addition, these PNCs are more structurally stable than CsPbCl3 and CsPbI3 ones. However, most exchange reactions in solution reported in published studies are spontaneous and poorly controllable. In this study, the anion exchange reaction is proposed to be carried out directly on the formed thin film of CsPbBr3 incorporated in the matrix of a copolymer of methyl and lauryl methacrylates. The exchange reactions with octadecylammonium iodide and PbI2 leading to a shift of the photoluminescence maxima to longer wavelengths by 130 and 137 nm within 15 and 6 min, respectively. The study also shows the possibility of carrying out an ion exchange reaction on a substrate mimicking the real structure of a light-emitting diode. Keywords: inorganic perovskite nanocrystals, anion exchange, thin films, photoluminescence.

Изменение люминесценции тонких нанокристаллических пленок перовскита CsPbBr-=SUB=-3-=/SUB=- в ходе реакции анионного обмена in situ

Inorganic perovskite CsPbX3 nanocrystals (PNCs), where X is a halide anion, are currently promising materials for a wide range of optoelectronic devices. One of the key tasks to be solved before they are used in practice is to obtain stable thin PNC films whose luminescence wavelength could be finely tuned. The chemical composition of CsPbX3 PNCs is the main parameter determining their band gap width and, hence, the position of their photoluminescence maximum. Variation of the PNC composition in the course of their synthesis or postsynthetic treatment in solution makes it possible to obtain CsPbBr(3–x)Ix and CsPbBr(3–y)Cly materials emitting in the entire visible spectral range. In addition, these PNCs are more structurally stable than CsPbCl3 and CsPbI3 ones. However, most exchange reactions in solution reported in published studies are spontaneous and poorly controllable. In this study, the anion exchange reaction is proposed to be carried out directly on the formed thin film of CsPbBr3 incorporated in the matrix of a copolymer of methyl and lauryl methacrylates. The exchange reactions with octadecylammonium iodide and PbI2 leading to a shift of the photoluminescence maxima to longer wavelengths by 130 and 137 nm within 15 and 6 min, respectively. The study also shows the possibility of carrying out an ion exchange reaction on a substrate mimicking the real structure of a light-emitting diode.

Stable and luminescent cesium copper halide nanocrystals embedded in flexible polymer fibers for fabrication of down-converting WLEDs.

Recently, CsPbX3 (X = I, Br, Cl) perovskite nanocrystals (NCs) have drawn wide attention owing to their outstanding photophysical and optoelectronic properties. However, the toxicity of such NCs remained a big challenge for further commercialization. Herein, we adopt facile methods for synthesizing green-emissive Cs3Cu2Cl5 and blue-emissive Cs3Cu2Br2.5I2.5 perovskite NCs that exhibit broad emission spectra with large Stokes shifts. These NCs showed photoluminescence quantum yields (PLQY) up to 65% (Cs3Cu2Cl5 NCs) and 32% (Cs3Cu2Br2.5I2.5 NCs) with limited stabilities. To further improve the stability, the NCs were blended with a hydrophobic polymer poly-methylmethacrylate (PMMA) and embedded inside the polymer fiber by an electrospinning process to form composite fibers. The as-prepared Cs3Cu2Cl5@PMMA and Cs3Cu2Br2.5I2.5@PMMA fiber films demonstrated good surface coverage and better thermal stability, and even retained their emission properties when dispersed in water. The emissive fibers were also deposited on flexible polyethylene terephthalate (PET) substrates that displayed high resistance towards bending and twisting with no signs of breakage, damage, or loss of optical properties. Finally, UV-pumped phosphor-converted WLEDs fabricated by using these blue and green-emitting fibers revealed CIE chromaticity coordinates at (0.27, 0.33) with a maximum luminous efficiency of 69 Lm W-1 and correlated color temperature (CCT) value of 8703 K. These outcomes can be beneficial for the development of futuristic flexible display technologies.

Synergetic effects of the co-doping transition metal ions and the silica-shell coating for enhancing the photoluminescence and stability of Mn: CsPbCl3 nanocrystals and their application

Doping Mn2+ ions into cesium lead halide CsPbX3 (X = Cl, Br, I) perovskite nanocrystals (PNCs) has been proven to be an effective strategy to reduce the Pb2+ content. However, excessive Mn2+ ions may form the Mn–Mn dimers in PNCs, leading to concentration quenching effects and low photoluminescence quantum yields (PLQYs). Herein, secondary metal ions (Ni2+, Cu2+, Zn2+) were introduced to substitute Pb2+ ions as co-doped (Mn, M):CsPbCl3 PNCs (M = Ni, Cu, Zn), which were prepared by a facile method under ambient conditions, aiming for positively passivating the surface defects and improving the Mn2+ emission. Also, to protect the co-doped (Mn, M):CsPbCl3 PNCs from moisture damage, we performed silica encapsulation, which further passivated surface defects due to the effective hydrolysis of silane. The evolution of optical properties and stabilities of three series of (Mn, M):CsPbCl3 PNCs was compared. The PLQYs of co-doped (Mn, M):CsPbCl3 PNCs were larger than those of single-doped Mn: CsPbCl3 PNCs, especially for (Mn, Ni):CsPbCl3 and (Mn, Cu):CsPbCl3, which can reach nearly 30%. The PLQYs of (Mn, Ni):CsPbCl3 and (Mn, Zn):CsPbCl3 PNCs decreased dramatically during the encapsulation process, while the PLQY values of (Mn, Cu):CsPbCl3 remained 30% even after the same treatment process. Consequently, the prototypes of white light-emitting devices (WLEDs) were successfully fabricated based on orange-red (Mn, Ni):CsPbCl3@SiO2 and (Mn, Zn):CsPbCl3@SiO2 composites. The synergetic effects of co-doping transition metal ions and silica-shell coating on improving optical properties and stabilities were investigated. It has potential for a wide range of applications in the field of solid-state light emission.

Magnetic and Electric Field Dependent Charge Transfer in Perovskite/Graphene Field Effect Transistors

AbstractStable all‐inorganic CsPbX3 perovskite nanocrystals (PNCs) with high optical yield can be used in combination with graphene as photon sensors with high responsivity (up to 106 A W−1) in the VIS‐UV range. The performance of these perovskite/graphene field effect transistors (FET) is mediated by charge transfer processes at the perovskite – graphene interface. Here, the effects of high electric (up to 3000 kV cm−1) and magnetic (up to 60 T) fields applied perpendicular to the graphene plane on the charge transfer are reported. The authors demonstrate electric‐ and magnetic‐field dependent charge transfer and a slow (>100 s) charge dynamics. Magneto‐transport experiments in constant (≈0.005 T s−1) and pulsed (≈1000 T s−1) magnetic fields reveal pronounced hysteresis effects in the transfer characteristics of the FET. A magnetic time is used to explain and model differences in device behavior under fast (pulsed) and slowly (continuous) changing magnetic fields. The understanding of the dynamics of the charge transfer in perovskite/graphene heterostructures developed here is relevant for exploitation of these hybrid systems in electronics and optoelectronics, including ultrasensitive photon detectors and FETs for metrology.