CsPbCl3 Nanocrystals Research Articles

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.

Enhanced Exciton‐to‐Mn2+ Energy Transfer in 3D/0D Cesium–Lead–Chloride Composite Perovskites

AbstractDoping cesium lead halide perovskite nanocrystals (NCs) with Mn2+ brings attractive long‐wavelength emission and flexible color tunability. However, due to multiple competing factors, the exciton‐to‐Mn2+ energy transfer efficiency is low. In this work, a simple structure‐optimization strategy is applied to enhance the exciton‐to‐Mn2+ energy transfer by synthesizing Mn2+ activated 3D/0D Cs–Pb–Cl perovskite composition composed of 3D CsPbCl3 and 0D Cs4PbCl6 NCs. The results reveal that the energy transfer efficiency and the photoluminescence quantum efficiency of the Cs–Pb–Cl composite are 65.3% and 77.3%, respectively, which are 1.4 and 3 times the corresponding values of the single‐phase CsPbCl3:Mn2+ NCs. Based on the detailed experimental and calculation results, the performance enhancement is demonstrated to stem from the optimized growth process of 3D CsPbCl3 NCs when co‐generating with 0D Cs4PbCl6 NCs. The strong lattice rigidity of the optimized CsPbCl3 NCs suppresses the nonradiative combination rate of the excitons, thus alleviating the main competing factor of the energy transfer process and improving the energy transfer efficiency. Fabrication of a white light‐emitting diode prototype further illustrates the application potential of the orange‐emitting Cs–Pb–Cl composite NCs for general lighting.

Filling Chlorine Vacancy with Bromine: A Two-Step Hot-Injection Approach Achieving Defect-Free Hybrid Halogen Perovskite Nanocrystals.

Mixed-halide (Cl and Br) perovskite nanocrystals (NCs) are of particular interest because they hold great potential for use in high-efficiency blue light-emitting diodes (LEDs). Generally, mixed-halide compounds are obtained by either a one-step synthesis with simultaneous addition of both halide precursors or a postsynthetic anion exchange using the opposite halogen. However, both strategies fail to prevent the formation of deep-level Cl vacancy defects, rendering the photoluminescence quantum yields (PLQYs) typically lower than 30%. Here, by optimizing both thermodynamic and kinetic processes, we devise a two-step hot-injection approach, which simultaneously realizes Cl vacancy filling and efficient anion exchange between Cl- and Br-. Both the identity of Br precursors and their injection temperature are revealed to be critical in transforming those highly defective CsPbCl3 NCs to defect-free CsPb(Cl/Br)3. The optimally synthesized NCs exhibit a saturated blue emission at ∼460 nm with a near-unity PLQY and a narrow emission bandwidth of 18 nm, which represents one of the most efficient blue emitters reported so far. The turn-on voltage of the ensuing LEDs is ∼4.0 V, which is lower than those of most other mixed-halide perovskites. In addition, LEDs exhibit a stable electroluminescence peak at 460 nm under a high bias voltage of 8.0 V. We anticipate that our findings will provide new insights into the materials design strategies for producing high-optoelectronic-quality Cl-containing perovskites.

Lead Halide Perovskite Cube Coupled Star Nanocrystal Photocatalysts

Ligand dynamics on the surface of nanocrystals plays a major role in controlling their successive layers growth. This has been widely established for chalcogenide nanomaterials but less explored for recently emerged halide perovskite nanocrystals. However, with the introduction of different non-lead metal (Cd and Mn) acetates/oxides to limit surface halide concentration and alkylammonium ion ligands, herein, star shaped cube coupled nanocrystals are reported, and their growth from less than 50 nm to nearly 500 nm is monitored. These acetates/oxides helped in inducing secondary growth along one of the {200} facets of parent orthorhombic CsPbBr3 cube nanocrystals and led to the unique star shaped nanocrystals which consumed smaller size cube nanocrystals and continued to grow further. The method is also extended to CsPbCl3 nanocrystals. Due to complex shapes, these are further explored as photocatalysts for CH4 and CO evolution under purging CO2 gas in ethyl acetate/water medium, and their catalytic activities are compared with cube nanocrystals.

Ligand regulated selective synthesis of Cs4PbCl6 microcrystals in microemulsion and their cathodoluminescence

In recent years, all-inorganic perovskite semiconductor CsPbCl3 is widely studied because of its excellent optical and electronic properties, but its derivative Cs4PbCl6, which possesses a wider band gap, is seldom studied due to the challenging synthesis. In this work, we demonstrate a selective synthesis method for Cs4PbCl6 and CsPbCl3 in microemulsion regulated by the ligand concentration of n-octylamine. When the concentration is sufficiently high, the products are regular hexagonal Cs4PbCl6 microcrystal in sizes of 1–2 μm; when the concentration is sufficiently low, the products are rectangular plate-shaped CsPbCl3 nanocrystals in sizes of 200–800 nm; and when the concentration is moderate, the products are their mixtures. Cathodoluminescence spectrum of a single particle of Cs4PbCl6 is measured. The change of Pb2+ solubility regulated by the ligand concentration is mainly responsible for the selective synthesis. This method applies for the synthesis of Cs4PbBr6.

Shallow trap mediated temperature-dependent exciton and Mn2+ photoluminescence in CsPbCl3:Mn2+ nanocrystals

As an effective means to endow lead halide perovskite nanocrystals (NCs) with new properties, ion doping has been widely applied. Transition metal Mn-doped CsPbCl3 is of particular interest, as the Mn doping introduces new emission bands, improves photoluminescence quantum yield (PLQY), and even enhances stability. However, it is still insufficient to catch insight of the energy transfer process and luminescence characteristics of these high defect tolerance NCs doped with Mn ion. Here, we systematically studied the energy transfer from exciton to Mn2+ ions in Mn-doped CsPbCl3 NCs by variable temperature steady-state fluorescence spectra and time-resolved spectra. The abnormal attenuation behavior of the exciton and Mn2+ with the change of temperature was observed, from which we predict the existence of shallow traps near the conduction band and these shallow traps will affect the luminescence properties by influencing the energy transfer process. We show a simple physical model invoking only shallow trap states that uniquely describe the temperature-dependent energy transfer between the exciton and the Mn2+ ion. The thermometric performance (30–290 K) was studied in terms of relative thermal sensitivity, in which the calculated relative sensitivity range is ∼0.12%–1% K−1.

Photoluminescence Properties of CsPbCl3 and CsPbBr3 Nanocrystals synthesized by LARP Method with Various Ligands and Anti-solvents

Cesium lead halide (CsPbX3; X= Cl, Br, I) is inorganic materials that can be used for the absorber of Perovskite solar cell and active layer of sensor. In this research, synthesis of cesium lead chloride (CsPbCl3) utilizes cesium chloride (CsCl) and lead (II) chloride (PbCl2) as raw materials then oleic acid and linoleic acid are used as ligands. CsCl and PbCl2 can be utilized to synthesize CsPbCl3 by using ligand-assisted reprecipitation (LARP) method at room temperature. Dimethyl Sulfoxide (DMSO) is used as the solvent of CsCl and PbCl2 to form 0.1 M solution. Similar to CsPbCl3, synthesis of CsPbBr3utilizes CsBr and PbBr2 at room temperature. Antisolvent used in this experiment are chloroform, toluene and tetrahydrofuran (THF) for colloidal solution CsPbCl3 and CsPbBr3. This research will analyze the impact of different ligands and different antisolvent, so it will be obtained the most suitable ligand and antisolvent for CsPbCl3 and CsPbBr3. The wavelength of photoluminescence spectra for samples of CsPbCl3 and CsPbBr3 colloidal solution are 434.00 nm and 512.82 nm. Based on transmission electron microscope (TEM) results, nanocrystals have been formed in samples of CsPbCl3 and CsPbBr3 colloidal solution. Powder samples of CsPbCl3 and CsPbBr3 can be obtained by heating at 190°C (the boiling point of DMSO) then CsPbCl3 and CsPbBr3 are identified in each powder sample by x-ray diffraction (XRD).

Nucleophile-Controlled Halide Release from the Substitution Reaction of Haloketone for Facet Tuning and Manganese Doping in CsPbCl3 Nanocrystals.

Halide content of the reaction medium not only enhances the brightness of CsPbCl3 nanocrystals but also, control the shape modulations as well as doping Mn(II) in these host nanocrystals. Correlating both the shape effect and doping, herein, an in situ reaction of nucleophile-controlled halide release was explored for monitoring facets modulations and doping in CsPbCl3 nanocrystals. This was performed using alkyl amine as nucleophile which reacted with α-halo ketone, phenacyl chloride, to release chloride ions. Increase in amine concentration which released more Cl ions, reduced the possibility of shape transformation from perfect to truncated cubes during annealing. Similarly, for Mn(II) doping, the dopant photoluminescence intensity remained directly proportional to the amount of introduced amine nucleophiles. Quality of both doped and undoped nanocrystals obtained in this procedure remained unparallel and the method provided a strong correlation of rate of halide release with both facet modulations and doping in these nanocrystals.

Mn‐Doped Perovskite Nanocrystals for Photocatalytic CO2 Reduction: Insight into the Role of the Charge Carriers with Prolonged Lifetime

As an emerged photocatalyst, perovskites have attracted enormous interest in photocatalysis due to their excellent photoelectronic properties. However, most of the photoexcited electron–hole pairs recombine together before they reach the surface of perovskite for photocatalysis. The undesired charge recombination would compete with the surface photocatalytic reaction. Hence, the regulation of charge carriers is essential for improving the photocatalytic performance of perovskites. Herein, the charge transfer dynamics by doping Mn2+ in CsPbCl3 perovskite nanocrystals (NCs) is manipulated and the role of the charge carriers with a prolonged lifetime in photocatalysis is investigated. The photogenerated charge carriers with a prolonged lifetime at both Mn2+ dopants and conduction band (CB) endow Mn:CsPbCl3 NCs with an enhanced photocatalytic activity toward CO2 reduction. The doping strategy provides us with a powerful tool to regulate the charge transfer dynamics in perovskite NCs for photocatalysis. It is believed that the long‐lived charge carriers in perovskite NCs have great potential in promoting charge separation and suppressing charge recombination in solar‐to‐fuel conversions.

Solvothermal synthesis of perovskite CsPbCl3 nanoplates and improved photoluminescence performance through postsynthetic treatment

The controllable synthesis of two-dimensional all-inorganic lead halide perovskite (CsPbX3, X = Cl, Br and I) nanoplates (NPLs) has attracted wide attention of researchers. However, the direct synthesis of high-quality CsPbCl3 NPLs with controllable morphology still faces a challenge. Herein we report a solvothermal method to directly synthesize CsPbCl3 NPLs. By varying solvothermal reaction time, the thickness of the NPLs has be successfully adjusted from 2.8 to 3.6 nm, and the red shift of the photoluminescence (PL) emission from 391 to 402 nm has been realized. Subsequently, effective post-treatment on the as-prepared CsPbCl3 NPLs using CoCl2 results in the greatly enhancement of PL quantum yield (PLQY) from original 14.09 to final 50.4%, showing the best PLQY among all CsPbCl3 NPLs samples to date. This work not only provides a reliable process for the controllable preparation of CsPbCl3 NPLs, but also supplies more selectivity for the post-treatment of CsPbCl3 nanocrystals using chloride compounds.

Thiophene Derivatives as Ligands for Highly Luminescent and Stable Manganese-Doped CsPbCl3 Nanocrystals.

Ligands on the surface of perovskite nanocrystals are important to stabilize the nanocrystal structure. However, the research of ligands on Mn2+ ion-doped CsPbCl3 nanocrystals (Mn: CsPbCl3 NCs), a promising candidate family for the lightning community, is relatively rare. Here, we demonstrate a new ligand modification strategy for preparing high-quality Mn: CsPbCl3 NCs by a simple hot-injection method. Thiophene derivative, for the first time, is applied as ligands for perovskite nanocrystals. The new ligands of thiophene derivatives passivate defects on the surface of NCs and enhance optical properties, originating from the sulfur in thiophene additives binding to the uncoordinated lead ions. The photoluminescence quantum yield of the modified Mn: CsPbCl3 NCs is 93% in comparison with 46% of the pristine counterparts, whose value is the highest to date for ligand-modified Mn: CsPbCl3 NCs. Meanwhile, the thermal, storage, and purification stability are also significantly improved. The performance of related LEDs is also investigated.

A-Site FA+ Doping-Enhanced Photoluminescence Efficiency and Photostability of Mn-Doped Perovskite Nanocrystals

Improving the optical and structural stability of highly luminescent Mn2+-doped CsPbCl3–yBry (Mn:CsPbCl3–yBry) nanocrystals (NCs) under ultraviolet illumination is very necessary for their application in solid-state lighting. Herein, greatly improved photoluminescence (PL) quantum yield (QY) and illumination stability were observed in Mn:CsPbCl3 NCs by incorporation of an appropriate FA+ amount into the crystal lattice. The Mn:FAxCs1–xPbCl3 NCs showed higher PL QYs (up to 76%), longer Mn2+ PL lifetimes, and nearly single-exponential decay relative to the Mn:CsPbCl3 ones. With the increase in irradiation time, a slowly reduced PL intensity and an almost unchanged PL peak position and linewidth of Mn2+ ions in Mn:FA0.15Cs0.85PbCl3 NCs were found, suggesting that the mixing of FA+ and Cs+ can increase the tolerance of the lattice and improve the photostability of the NCs. Under high-power ultraviolet irradiation, the light-induced Mn2+ PL attenuation of Mn:FA0.15Cs0.85PbCl3 NCs was slower than that of the ones without FA+, and no divisive emission peaks representing Br-rich and Cl-rich regions appeared in Mn:FA0.15Cs0.85PbCl3–yBry NCs, which was consistent with the result that the X-ray diffraction peaks of the NCs with FA+ remained constant with irradiation time. This indicates that severe Mn2+ ion diffusion and halogen ion segregation can be effectively inhibited by adding FA+ into the Mn-doped perovskite NCs.

Aluminum chloride assisted synthesis of near-unity emitting Mn2+-doped CsPbCl3 perovskite nanocrystals for bright white light-emitting diodes

Enhanced orange-red emitting Mn2+-doped CsPbCl3 nanocrystals with a near-unity photoluminescence quantum yield of up to 98% are synthesized through an AlCl3-assisted hot-injection route.

Halide Perovskite Nanocrystal-Enabled Stabilization of Transition Metal Dichalcogenide Nanosheets.

Transition metal dichalcogenide (TMD) nanosheets exfoliated in the liquid phase are of significant interest owing to their potential for scalable and flexible photoelectronic applications. Although various dispersants such as surfactants, oligomers, and polymers are used to obtain highly exfoliated TMD nanosheets, most of them are electrically insulating and need to be removed; otherwise, the photoelectric properties of the TMD nanosheets degrade. Here, inorganic halide perovskite nanocrystals (NCs) of CsPbX3 (X = Cl, Br, or I) are presented as non-destructive dispersants capable of dispersing TMD nanosheets in the liquid phase and enhancing the photodetection properties of the nanosheets, thus eliminating the need to remove the dispersant. MoSe2 nanosheets dispersed in the liquid phase are adsorbed with CsPbCl3 NCs.The CsPbCl3 nanocrystals on MoSe2 efficiently withdraw electrons from the nanosheets, and suppress the dark current of the MoSe2 nanosheets, leading to flexiblenear-infrared MoSe2 photodetectors with a high ON/OFF photocurrent ratio and detectivity. Moreover, lanthanide ion-dopedCsPbCl3 NCs enhancethe ON/OFF current ratio to >106 . Meanwhile, the dispersion stability of the MoSe2 nanosheets exfoliated with the perovskite NCs is sufficiently high.

Enhanced photoluminescence efficiencies of CsPbCl3-xBrx nanocrystals by incorporating neodymium ions

All-inorganic perovskite nanocrystals (NCs) are emerged as promising materials for illumination and display applications due to their excellent luminescent properties. However, the low photoluminescence quantum yield (PLQY) of violet/blue emission and poor stability of NCs restrict their development. Herein, we report an effective strategy for enhanced PLQY and stability of CsPb(Cl/Br)3 NCs by incorporating Nd3+ ions. It was found that Nd3+ ions could be doped into the host perovskite NC lattice which exists in NCs as Nd3+. The steady-state and time-resolved PL spectra showed the decrease of the defect state density in doped NCs with the increase of Nd content. The maximum PLQY of the as-prepared Nd3+ doped CsPbCl3 NCs was increased up to 58% at the Nd/Pb molar ratio of 3/1. Compared with undoped NCs, the water stability of Nd3+ doped CsPbCl3 NCs was significantly improved. The prepared Nd3+ doped CsPbCl3 NCs were further post-treated by anion exchange reaction with PbBr2 at room temperature. The PL of the as-synthesized Nd3+ doped CsPb(Cl/Br)3 NCs covered the emission range of 408–503 nm, and the maximum PLQY could reached 93%. This work discourses that Nd3+ ions can improve the PLQY and stability of blue and violet perovskite NCs, which will promote their practical application.

Simultaneous Enhancement of Photoluminescence and Stability of CsPbCl3 Perovskite Enabled by Titanium Ion Dopant

The application of CsPbCl3 perovskite is limited by the low photoluminescence quantum yield (PLQY), weak luminescence, and unpromising stability. Doping impurity ions has been considered as an effective strategy to tune the optoelectronic performances of perovskite. In this work, heterovalent Ti3+ ions are successfully doped into CsPbCl3 nanocrystals. It is found that Ti3+ ion doping could effectively improve the photoluminescence (PL) performance of CsPbCl3 nanocrystals. Density functional theory (DFT) calculations reveal that Ti3+ ions could introduce more band-edge states around the conduction band minimum of CsPbCl3, which is conducive to release electrons into conduction band. Furthermore, Ti3+ ion doping could inhibit the Cl vacancy concentration in CsPbCl3 and prevent the in-gap state caused by Cl vacancy. Notably, the stability of CsPbCl3 perovskite is greatly improved through Ti3+ ion doping. This work provides a new perspective for improving the optoelectronic properties of all-inorganic perovskites through heterovalent metal ion doping.

Perovskite energy funnels for efficient white emission

Doping Mn2+ into CsPbCl3 nanocrystals (NCs) yields strong orange emission, while the related emission in Mn2+ doped CsPbBr3 NCs is impaired seriously. This is mainly ascribed to back energy transfer from the Mn2+ dopant to the host. Doping Mn2+ into perovskites with multiple-quantum-well (MQW) structures may address this issue, where the energy funnels ensure a rapid energy transfer process, and thus resulting in a high photoluminescence quantum yield (PLQY). Here, we have developed an Ag+ assisted Mn2+ doping method in which Mn2+ can be easily doped into Br-based MQW perovskites. In this MQW perovskites, both nanoplatelets (NPLs) and NCs were formed simultaneously, where efficient energy transfer occurred from the NPLs with a higher energy bandgap to the NCs with a smaller energy bandgap, and then to the Mn2+ dopants. White lighting solution with a PLQY up to 98% has been acquired by altering the experimental parameters, such as reaction time and the Pb-to-Mn feed ratio. The successful doping of Mn2+ into CsPbBr3 host has great significance and shows promising application for next-generation white lighting.

Synthesis and optical properties of doped CsPbCl3 nanocrystals

Synthesis and optical properties of doped CsPbCl3 nanocrystals

Narrow-Band Violet-Light-Emitting Diodes Based on Stable Cesium Lead Chloride Perovskite Nanocrystals

CsPbCl3 nanocrystals are potential ultrapure emitters. But it is challenging to synthesize CsPbCl3 nanocrystals with sufficient stability, which impedes their application in light-emitting devices. In this work, we report a facile phosphoryl-chemistry-mediated synthesis approach to synthesizing stable CsPbCl3 nanocrystals, in which the phenylphosphonic dichloride (PhPOCl2) precursor is employed. In addition to the high reactivity of the P–Cl bond of PhPOCl2 for providing adequate Cl, the derived P=O with good proton affinity facilitates the formation of a distinct nanocrystal surface with the nonprotonated oleylamine (OLA) ligand. Accordingly, the L-type-ligand-capped CsPbCl3 nanocrystals exhibited not only bright luminance but also good stability that endured repeated purification up to 10 cycles. Based on the stable CsPbCl3 nanocrystals, we achieved violet LEDs with extremely narrow electroluminescence spectra (full width at half-maximum ≈ 10.6 nm).

Revealing the effect of electrochemical switching and energy transfer on the electrochemiluminescence of Mn-doped CsPbCl3 nanocrystals

The electrochemical behavior and consequent luminescence properties of Mn-doped CsPbCl3 perovskite (Mn:CsPbCl3) nanocrystals (NCs) were investigated by cyclic voltammetry (CV) and electrochemiluminescence (ECL) measurements. Mn:CsPbCl3 NCs could be electrochemically injected with electrons or holes at different potentials to produce ECL through both annihilation and coreactant routes. Importantly, it has been found that the ECL involving the coreactant could originate from two pathways: energy recombination at the surface, and energy transfer from the excited CsPbCl3 host to the dopant center, producing emission via Mn d-d transition, which is different from the photoluminescence (PL) of Mn:CsPbCl3 NCs alone, which contains dual emissions from both the host and the dopant.