CsPbCl3 Nanocrystals Research Articles

The correlation between phase transition and photoluminescence properties of CsPbX3 (X= Cl, Br, I) perovskite nanocrystals.

We report a correlation between the structural phase transition of CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) and their temperature-dependent steady-state photoluminescence (PL) and time-resolved PL (TRPL). In contrast to CsPbBr3 and CsPbI3 NCs which exhibited a continuous blue-shift in their band gap with increasing temperature, the CsPbCl3 exhibited a blue shift until ∼193 K, followed by a red shift until room temperature. We attribute this change from a blue to a red shift to a structural phase transition in CsPbCl3, which also manifested in the temperature dependent TRPL. This pronounced phase transition in CsPbCl3 NCs is probably due to the condensation of its vibrational modes at low temperature, and the presence of the weak quantum confinement effect. Notably, the exciton recombination lifetimes showed a similar reverse trend due to the phase transition in CsPbCl3, which has not been reported previously.

Carbon-based fully printable self-powered ultraviolet perovskite photodetector: Manganese-assisted electron transfer and enhanced photocurrent

In this work, we improved the photocurrent of self-powered ultraviolet photodetector via doping manganese in CsPbCl3 perovskite nanocrystals light harvester. The doped manganese in nanocrystals has the following three features to assist electron transfer from CsPbCl3 nanocrystals to titanium dioxide: (i) the fast exciton-to-manganese energy transfer process benefits for competing electrons with perovskite exciton recombination, (ii) the charge carrier lifetime is very long for manganese d-states due to its spin and orbital forbidden transition, and (iii) the electrons can effectively transfer to the titanium dioxide layer from 4T1 of manganese d-states due to the smaller energy barrier. Based on the above, the self-powered photocurrent density of photodetectors has nearly twice enhancement from 0.08 mA·cm−2 to 0.14 mA·cm−2 and a high responsivity up to 7.3 mA·W−1 was achieved at 340 nm.

Mechanochemical synthesis and characterization of Mn-doped CsPbCl3 perovskite nanocrystals

Mn-doped CsPbCl3 nanocrystals are considered to be a promising material for luminescence and display applications owing to Mn doping provides a way to introduce new optical properties and reduce the use of toxic Pb. Complicate ion-exchange and hot-injection are commonly used for the fabrication of the nanocrystals. Developing a fast and efficient synthesis method remains a challenge so far. Herein, we developed a simplified solid-state mechanochemical approach to synthesize Mn-doped CsPbCl3 nanocrystals and investigated the structure and luminescence properties of the as-synthesized nanocrystals. Cubic morphology of Mn-doped CsPbCl3 nanocrystals with average size of 13 nm have been obtained by this approach. Mn was successfully incorporated in CsPbCl3 perovskite nanocrystals, resulting in a high photoluminescence quantum yield of 40.7% with an improvement of stability. Emission peak of 594 nm that can be assigned to the luminescence of Mn2+ d-d transition was observed under 365 nm UV excitation. The color of the luminescence changed from blue to warm white to yellow depended on the amount of Mn doping, exhibiting a tunable-color property. It is expected that this approach provides an effective route that would help for synthesis of perovskite nanocrystals doped with different dopants.

Origin and tunability of dual color emission in highly stable Mn doped CsPbCl3 nanocrystals grown by a solid-state process

Herein, we report on a facile, bulk scale room temperature solid-state synthesis of highly stable and luminescent Mn-doped CsPbCl3 nanocrystal (NCs) with high Mn substitution, and investigate the origin and tunability of its dual-color emission. The structural and compositional analyses confirm the successful doping of Mn (1–40%) ion in CsPbCl3 NCs. The Mn-doped CsPbCl3 NCs exhibit distinct excitonic photoluminescence (PL) emission at ~412 nm (Iex) and Mn related emission at ~590 nm (IMn) with high PL quantum yield (up to 35%). Our study reveals that the intensity ratio IMn/Iex could be widely tuned by a factor of 64 and 23 by changing the Mn concentration and the measurement temperature, respectively. The stronger Mn emission at higher temperature is attributed to the higher rate of transfer of photoexcited carriers from the excitonic state of CsPbCl3 host to Mn related state. Further, excitation intensity-dependent PL along with time-resolved PL studies revealed important insights into the origin and tunability of Mn related orange-red PL in the dual color emitting Mn-doped CsPbCl3 NCs. The PL line shape analysis revealed additional PL peak in the range ~634–666 nm, which grows stronger with higher doping concentration and it is attributed, for the first time, to structural defects in the NCs. Remarkably, the Mn-doped CsPbCl3 NCs synthesized by our method exhibit about 10 times higher storage stability than those reported earlier due to the high Mn doping efficiencies achieved due to the strain induced enhanced doping process. Finally, white light emitting diodes (LEDs) were fabricated by employing blue-emitting CsPbCl1.5Br1.5 NCs, green-emitting CsPbBr3 NCs and orange-red emitting 10% Mn-doped CsPbCl3 NCs all grown by the same method. Our work demonstrates a low-cost synthesis strategy for high Mn doping in CsPbCl3 NCs with superior ambient stability and highly tunable emission.

Mechanistic understanding of the charge carrier trapping in CsPbCl3 perovskite nanocrystals

The optical properties of CsPbCl3 perovskite nanocrystals (NCs) with varied sizes were studied in the temperature range from 80 to 320 K by steady-state and time-resolved photoluminescence (PL) spectroscopy. The CsPbCl3 NCs were synthesized with a hot-injection approach at reaction temperature of 140–180 °C. The PL emissions in NC films originate from localized excitons. It is found that NC films shows a significant decrease in PL intensity with increasing temperature while they exhibit a clear increase in PL lifetime from 80 K to around 250 K and then a reduction at high temperature. The abnormal temperature dependence of PL lifetimes in NC films is related to thermal activation of trapped carriers in the NCs. The change of average lifetimes with emission energy indicates the thermal degradation result from the loss of ligands on the surface of NC films. Moreover, the PL intensities, peak energies, and bandwidths of the NC films as a function of temperature are discussed detail.

Picosecond electron trapping limits the emissivity of CsPbCl3 perovskite nanocrystals.

Lead halide perovskite nanocrystals (NCs) have emerged as enabling materials for optoelectronics and photonics. A parameter essential for these applications is the photoluminescence quantum yield (PL QY) of these NCs. Despite being generally conceived as "defect-tolerant," perovskite NCs often have PL QYs significantly lower than unity, particularly for CsPbCl3 NCs with QYs typically lower than 10%. Postsynthetic treatments by (pseudo)halide salts were found to effectively improve the PL QYs, but the exact role played by the treatments (i.e., passivating electron and/or hole trapping sites) remains unclear. Here, we performed a side-by-side comparison between as-prepared and treated CsPbCl3 NCs using transient absorption and time-resolved PL measurements of sub-ps time resolution. We clearly identify ps electron trapping as the dominant channel impairing the PL QYs of as-prepared CsPbCl3 NCs. Electron trapping is effectively alleviated in the halide salt treated NCs. These insights should allow for rational improvement of the emissivity of perovskite NCs for the above-mentioned applications.

Coexisting CsPbCl3:CsPbI3 perovskite nanocrystal glasses with high luminescence and stability

Many previous studies have reported that because of the large difference between the ionic radii of Cl and I, halogen exchange is difficult to occur between CsPbCl3 and CsPbI3 perovskite nanocrystals, and the interaction between CsPbCl3 and CsPbI3 NCs will lead to their dissolution. In this work, two kinds of nanocrystals, CsPbCl3 and CsPbI3, were successfully crystallized simultaneously in glass by an in-situ growth method for the first time. Because of the effective reabsorption of photons, the CsPbCl3:CsPbI3 nanocrystals displayed higher fluorescence emission intensity and higher photoluminescence quantum yield than those of CsPbI3 nanocrystals. In addition, CsPbCl3:CsPbI3 nanocrystal glasses showed excellent water resistance and thermal stability, which benefited from the effective protection of the glass matrix. In particular, the fluorescence intensity of the nanocomposites remained above 95% after immersion in water for 60 days. Light-emitting devices were prepared by combining a near-infrared-emitting CsPbCl3:CsPbI3 nanocrystal glass and 400 nm LED chip, which were applied to indoor plant growth.

Optical properties of CsPbCl3 nanocrystals in phosphate glass

CsPbCl3 nanocrystals embedded glasses have potential to incorporate transition metal ions and lead to efficient spectral conversion for applications as solar concentrator materials in building. Here, CsPbCl3 nanocrystals were precipitated through heat-treatment in phosphate glasses with potential application in building. X-ray diffraction patterns confirm that CsPbCl3 nanocrystals were formed in glasses. By changing the heat-treatment conditions, absorption peaks of the CsPbCl3 nanocrystals can be tuned from 3.06 eV (405 nm) to 3.25 eV (381 nm). Upon 255–325 nm UV light excitation, photoluminescence in the range of 350–530 nm was observed. Upon 325–375 nm UV light excitation, CsPbCl3 nanocrystals exhibited narrow band photoluminescence centering at 405–410 nm with Stokes shift almost linearly dependent on the band gap energy of CsPbCl3 nanocrystals.

Synthesis of high-efficient Mn2+ doped CsPbCl3 perovskite nanocrystals in toluene and surprised lattice ejection of dopants at mild temperature

Doping has been established as a powerful approach for endowing novel properties to perovskite nanocrystals (NCs).However, the fast formation of perovskites makes the fundamental understanding of doping processes in these NCs very rare. In the present work, a mild temperature (<100 °C) approach to produce Mn2+ doped CsPbCl3 (Mn:CsPbCl3) perovskite NCs in toluene is reported. The effects of the introduced Mn/Pb ratios in the raw materials as well as the temperature on the structure and photoluminescence (PL) properties of Mn:CsPbCl3 NCs were investigated systematically. The as-synthesized Mn:CsPbCl3 NCs shown a strong Mn2+ emission at 594 nm with a PL quantum yield (QY) of 52%, and the doping concentrations can be easily tailored from 1.8 atom% to 13.3 atom% by changed the Mn/Pb feed ratios. The study revealed that the reaction temperature plays a key role in Mn:CsPbCl3 NCs. Through elemental and microstructure characterization, it was surprisingly found that lattice ejection of Mn ions occurred at 100 °C. This result greatly enhances the understanding of the “basic process” of Mn2+doping in CsPbCl3 NCs, which provides some insights into the preparation of metal ion doped perovskite NCs.

Improved Doping and Emission Efficiencies of Mn-Doped CsPbCl3 Perovskite Nanocrystals via Nickel Chloride.

It is challenging to improve the emission efficiency of Mn-doped CsPbCl3 (Mn:CsPbCl3) nanocrystals (NCs) because the excellent optical performances are dependent on high doping efficiency and few defects and traps. Steady-state and time-resolved photoluminescence (PL) spectroscopies were used to investigate the luminescence properties of Mn:CsPbCl3 NCs with different Mn doping levels synthesized in the presence of nickel chloride. The doping efficiency of Mn ions in Mn:CsPbCl3 NCs was greatly enhanced in the presence of NiCl2, and the PL wavelength of Mn2+ ions was tuned from 594 to 638 nm by varying the concentration of dopant Mn from 0.11% to 15.25%. The high emission quantum yields of Mn:CsPbCl3 NCs with orange and red emissions peaked at 600 and 620 nm in hexane were 70% and 39%, respectively. The improvement in doping and emission efficiencies of Mn2+ was attributed to the enhanced formation energies of the Mn doping under the Mn and Ni codoped configuration and the resulting reduction of defects and traps in Mn:CsPbCl3 NCs with incorporation of Ni2+ ions.

Highly Luminescent Violet- and Blue-Emitting Stable Perovskite Nanocrystals

Among the lead halide perovskites, photoluminescence quantum yield (PLQY) of violet-emitting CsPbCl3 nanocrystals (NCs) is the lowest (<5%). This is an impediment to the development of perovskite-b...

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.

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...

Engineering the Photoluminescence of CsPbX3 (X = Cl, Br, and I) Perovskite Nanocrystals Across the Full Visible Spectra with the Interval of 1 nm.

Fluorescent CsPbX3 (X = Cl, Br, I) perovskite nanocrystals (NCs) are compelling candidates for illumination and display applications because of the high photoluminescence quantum yields (PLQYs) narrow PL emission spectra, and in particular, the potential to tune the emission spectra in the entire visible range. However, limited by the current preparation strategy, the successive adjustment of PL emission across the full visible spectral range with very small interval, like conventional semiconductor quantum dots, is still challenging. In this work, we demonstrate the capability to tune the PL emission of CsPbX3 NCs in the full visible range with the interval of 1 nm on the basis of a modified anion-exchange route. Highly luminescent CsPbCl3 NCs with PLQY up to 34.2% are foremost prepared using alkanoyl chlorides as the chlorine source and further employed to perform anion exchange. A successive and accurate adjustment of the PL emission is achieved with the addition of ZnX2 (X = Br and I) aqueous solution and assisted by ultrasound to improve the reactivity of halogens in the anion exchange. Besides the accurately tunable PL emission position, the as-prepared CsPbX3 NCs exhibit good phase/chemical stability, high PLQY, and narrow PL emission spectra.

Presence of Metal Chloride for Minimizing the Halide Deficiency and Maximizing the Doping Efficiency in Mn(II)-Doped CsPbCl3 Nanocrystals.

Pretreatment using metal chlorides during the formation of halide deficient free perovskite nanocrystals is reported. Among several metal chlorides, Cu(II)Cl2 was observed to be ideal for the synthesis of highly emitting CsPbCl3 nanocrystals at high reaction temperature. Because high temperature remained more favorable for the dopant insertion, doping of Mn(II) was carried out under this halide-rich system, and nearly 68% photoluminescence quantum yield was recorded. Analysis could not provide strong evidence of insertion of Cu(II) inside the nanocrystals; rather, it was established that Cu(II)Cl2 in the system helped to stabilize the reaction even at and above 260 °C and provided an adequate chloride source for obtaining the highly emitting host as well as doped nanocrystals. Details of the physical process involved for this metal ion-induced uplifting of the reaction temperature and the consequent impacts on the nanocrystal formation are studied in detail and reported in this Letter.

Stable Luminous Nanocomposites of Confined Mn2+-Doped Lead Halide Perovskite Nanocrystals in Mesoporous Silica Nanospheres as Orange Fluorophores.

Creating highly stable inorganic perovskite nanocrystals (CsPbX3, where X = Cl, Br, and I) with excellent optical performance is challenging because their optical properties depend on their ionic structure and its inherent defects. Here, we present a facile and effective synthesis using a nanoconfinement strategy to grow Mn2+-doped CsPbCl3 nanocrystals embedded in dendritic mesoporous silica nanospheres (MSNs). The resulting nanocomposite is abbreviated as Cs(Pb x/Mn1- x)Cl3@MSNs and can serve as the orange emitter for white light-emitting diodes (WLEDs). The MSN matrix was prepared via a templated sol-gel technique as monodispersed center-radial dendritic porous particles, with a diamater of ∼105 nm and an inner pore size of ∼13 nm. The MSN was then utilized as the matrix to initiate the growth of Mn-doped perovskite nanocrystals (NCs). The NCs in the resulting composite have an average diameter of 8 nm and a photoluminescence quantum yield of >30%. In addition, the optical properties of the Cs(Pb x/Mn1- x)Cl3@MSNs can be tuned by varying the Mn2+ doping level. The resulting composites presented a significantly improved resistance to ultraviolet (UV) light, temperature, and moisture compared to that of bare Cs(Pb0.72/Mn0.28)Cl3. Finally, we fabricated down-converting WLEDs by using Cs(Pb x/Mn1- x)Cl3@MSNs as the orange-emitting phosphor deposited onto UV-emitting chips, demonstrating their promising applications in solid-state lighting. This work provides a valuable approach to fabricating stable orange luminophores as replacements for traditional emitters in light-emitting diode devices.

Grinding Synthesis of APbX3 (A = MA, FA, Cs; X = Cl, Br, I) Perovskite Nanocrystals.

Currently, metal halide perovskite nanocrystals have been extensively explored due to their unique optoelectronic properties and wide application prospects. In the present work, a facile grinding method is developed to prepare whole-family APbX3 (A = MA, FA, and Cs; X = Cl, Br, and I) perovskite nanocrystals. This strategy alleviates the harsh synthesis conditions of precursor dissolution, atmosphere protection, and high temperature. Impressively, the as-prepared perovskite nanocrystals are evidenced to have halogen-rich surfaces and yield visible full-spectral emissions with maximal photoluminescence quantum yield up to 92% and excellent stability. Additionally, the grinding method can be extended to synthesize widely concerned Mn2+-doped CsPbCl3 nanocrystals with dual-modal emissions of both excitons and dopants. As a proof-of-concept experiment, the present perovskite nanocrystals are demonstrated to be applicable as blue/green/red color converters in UV-excitable white-light-emitting diodes.

Temperature-dependent photoluminescence of pure and Mn-doped CsPbCl3 nanocrystals

Temperature-dependent photoluminescence (PL) properties of Mn-doped CsPbCl3 nanocrystals (NCs) are studied and compared with pure CsPbCl3 NCs by use of steady-state and time-resolved PL spectroscopies. The intrinsic exciton PL of the CsPbCl3 NCs locates at the wavelength range from 405 to 410 nm. The PL intensity in this range decreases rapidly, and the bandgap and linewidth become wider with rising temperature from 78 to 350 K. It is found that the exciton PL shows biexponential kinetics. The short-lived emission is ascribed to the surface trapping state recombination in NCs that has a photoinduced trapped pathway and a temporally resolved peak shift. The long-lived component is due to the band-edge excitonic recombination. Mn dopant open a new emission window at the wavelength range from 560 to 680 nm, of which intensity increases from 140 to 270 K, and then decreases with rising temperature up to 350 K. This unusual temperature dependence is ascribed to the thermal-assisted transition from the excitonic state of NCs to the 4T1 energy level of Mn2+. This work shows the potential of transition metal element doped perovskite NCs that can take advantage of the coupling between excitons and the d electrons of the dopants for expanded functionalities, such as temperature sensor and light-emitting diode.

High-Performance All-Inorganic CsPbCl3 Perovskite Nanocrystal Photodetectors with Superior Stability.

All-inorganic perovskites nanostructures, such as CsPbCl3 nanocrystals (NCs), are promising in many applications including light-emitting diodes, photovoltaics, and photodetectors. Despite the impressive performance that was demonstrated, a critical issue remains due to the instability of the perovskites in ambient. Herein, we report a method of passivating crystalline CsPbCl3 NC surfaces with 3-mercaptopropionic acid (MPA), and superior ambient stability is achieved. The printing of these colloidal NCs on the channel of graphene field-effect transistors (GFETs) on solid Si/SiO2 and flexible polyethylene terephthalate substrates was carried out to obtain CsPbCl3 NCs/GFET heterojunction photodetectors for flexible and visible-blind ultraviolet detection at wavelength below 400 nm. Besides ambient stability, the additional benefits of passivating surface charge trapping by the defects on CsPbCl3 NCs and facilitating high-efficiency charge transfer between the CsPbCl3 NCs and graphene were provided by MPA. Extraordinary optoelectronic performance was obtained on the CsPbCl3 NCs/graphene devices including a high ultraviolet responsivity exceeding 106 A/W, a high detectivity of 2 × 1013 Jones, a fast photoresponse time of 0.3 s, and ambient stability with less than 10% degradation of photoresponse after 2400 h. This result demonstrates the crucial importance of the perovskite NC surface passivation not only to the performance but also to the stability of the perovskite optoelectronic devices.

Anion Exchange and the Quantum-Cutting Energy Threshold in Ytterbium-Doped CsPb(Cl1- xBr x)3 Perovskite Nanocrystals.

Colloidal halide perovskite nanocrystals of CsPbCl3 doped with Yb3+ have demonstrated remarkably high sensitized photoluminescence quantum yields (PLQYs), approaching 200%, attributed to a picosecond quantum-cutting process in which one photon absorbed by the nanocrystal generates two photons emitted by the Yb3+ dopants. This quantum-cutting process is thought to involve a charge-neutral defect cluster within the nanocrystal's internal volume. We demonstrate that Yb3+-doped CsPbCl3 nanocrystals can be converted postsynthetically to Yb3+-doped CsPb(Cl1- xBr x)3 nanocrystals without compromising the desired high PLQYs. Nanocrystal energy gaps can be tuned continuously from Eg ≈ 3.06 eV (405 nm) in CsPbCl3 down to Eg ≈ 2.53 eV (∼490 nm) in CsPb(Cl0.25Br0.75)3 while retaining a constant PLQY above 100%. Reducing Eg further causes a rapid drop in PLQY, interpreted as reflecting an energy threshold for quantum cutting at approximately twice the energy of the Yb3+2F7/2 → 2F5/2 absorption threshold. These data demonstrate that very high quantum-cutting energy efficiencies can be achieved in Yb3+-doped CsPb(Cl1- xBr x)3 nanocrystals, offering the possibility to circumvent thermalization losses in conventional solar technologies. The presence of water during anion exchange is found to have a deleterious effect on the Yb3+ PLQYs but does not affect the nanocrystal shapes or morphologies, or even reduce the excitonic PLQYs of analogous undoped CsPb(Cl1- xBr x)3 nanocrystals. These results provide valuable information relevant to the development and application of these unique materials for spectral-shifting solar energy conversion technologies.