CsPbCl3 Nanocrystals Research Articles

Thermally stable emission from Yb3+-doped CsPbCl3 nanocrystals

The thermal stability of Yb3+-doped CsPbCl3 nanocrystals is critical for their performances and applications. In this work, we examine the high temperature luminescent properties of Yb3+-doped CsPbCl3 nanocrystals by temperature dependent luminescent spectroscopy (both steady and time-resolved). It is found that Yb3+ emission intensity first increases with temperature (300 K–350 K) and remains thermally stable up to 400 K. The initial PL increase is accompanied by the lengthening of decay lifetime and can be attributed to the removal of water molecules from the NCs’ surface, which can efficiently suppress the multi-phonon quenching and subsequently gives rise to PL enhancement and lifetime lengthening. Such thermally stable emission is originated from sub-picosecond carrier trapping by Yb3+ dimer, which is nearly 1000 times faster than that of native traps. Further increasing the temperature (400 K–480 K) leads to the reducing of PL intensity. The Yb3+ emission intensity drops to 53% of initial value at 480 K and suffers ∼20% irreversible loss after cooling back to 300 K. Formation of deep band-gap trap states and photon inactive species Cs4PbCl6 are responsible for PL decreasing and irreversible loss. Current report demonstrates the superior thermal stability of Yb3+ compared to exciton emission in perovskite NCs and shed new light on exploration of thermally stable luminescent materials.

Size-Dependent Doping Synergy and Dual-Color Emission in CsPb1-xMnxCl3 Nanocrystals

The doping of atomic impurities into colloidal semiconductor nanocrystals (NCs) is a powerful way to tune optical and electronic properties. Manganese (Mn)-doped CsPbCl3 NCs in particular show dual exciton/dopant emission in the visible spectrum, making them materials of current interest for optoelectronic applications. Here, we examine the impact of Mn doping on the photophysics of CsPbCl3 NCs from a different perspective. Using ultracentrifugation, we extract size-resolved fractions from a series of parent NC suspensions prepared at varied doping levels, and we measure the photoresponse as a function of NC size. Our results reveal synergistic radiative effects, with large enhancements in both blue (exciton) and red (dopant) quantum yield (QY) over a narrow range of Mn concentration. We ascribe the first effect to defect passivation and the latter to efficient exciton–dopant charge transfer near a critical point in the number of Mn per NC where the dopant spacing coincides with the Bohr exciton radius. Advanced computational techniques applied to Mn-doped CsPbCl3 reproduce emission colors and concentration trends, with a drop in QY at higher doping levels. Our results offer additional insight into the photophysical interplay of doping, quantum confinement, and radiative relaxation in lead-halide perovskites, while clarifying the complexity of the underlying kinetics and highlighting the critical role of the dopant number per NC at the nanoscale.

Recent Advances in Enhancing and Enriching the Optical Properties of Cl‐Based CsPbX3 Nanocrystals

AbstractCsPbCl3 nanocrystals (NCs) exhibit vast potential in high‐energy emission applications owing to their wide‐bandgap characteristics, that differ from those of CsPbBr3 and CsPbI3 NCs. Recently, significant developments related to CsPbCl3 NCs have been achieved with regard to tunable emission, luminescence efficiency, and stability, along with their use as hosts for the sensitization of transition metals or rare‐earth ions. This review describes the important factors that influence the optical properties of CsPbCl3 NCs based on factors such as crystal structure, defect compositions, and surface states. In addition, fundamental strategies for improving the performance of CsPbCl3 NCs are discussed, including direct synthesis, post‐treatment methods, and cation doping by either single‐ or co‐doping. The prospects of CsPbCl3 NCs for related optoelectronic applications are reviewed, with emphasis on practical hurdles that need to be overcome in the future.

Engineering the Bandgap and Surface Structure of CsPbCl3 Nanocrystals to Achieve Efficient Ultraviolet Luminescence

AbstractHerein, we report the design of novel ultraviolet luminescent CsPbCl3 nanocrystals (NCs) with the emission peak at 381 nm through doping of cadmium ions. Subsequently, a surface passivation strategy with CdCl2 is adopted to improve their photoluminescence quantum yield (PLQY) with the maximum value of 60.5 %, which is 67 times higher than that of the pristine counterparts. The PLQY of the surface passivated NCs remains over 50 % after one week while the pristine NCs show negligible emission. By virtue of density functional theory calculations, we reveal that the higher PLQY and better stability after surface passivation may result from the significant elimination of surface chloride vacancy (VCl) defects. These findings provide fundamental insights into the optical manipulation of metal ion‐doped CsPbCl3 NCs.

Precise Ligand Tuning Emission of Mn-Doped CsPbCl3 Nanocrystals by the Amount of Sulfonates.

Using Mn-doped CsPbCl3 nanocrystals (Mn:CsPbCl3 NCs) to improve perovskite's properties is becoming an important strategy. Here, we demonstrate a modified supersaturated recrystallization route to synthesize high-quality Mn:CsPbCl3 NCs at room temperature. Unprecedentedly, sulfonate ligands with various concentrations are shown to successfully tune the dual-color emission of Mn:CsPbCl3 NCs. Ultrafast transient absorption studies reveal that the host-to-dopant internal energy-transfer process involves the mediated traps. Interestingly, the dual-color emission is tuned via stabilizing mediated traps with a small amount of ligand (band edge (BE) emission reduces and Mn2+ emission increases), passivating the deep traps with a large amount of ligand (Mn2+ emission increases), and destroying Mn:CsPbCl3 NCs with too much ligand (both BE and Mn2+ emission is quenched). Furthermore, the ligand tuning Mn2+ emission exhibits quenching for Cu2+ with high sensitivity and selectivity. Our work provides a new strategy to tune the optical properties of Mn:CsPbCl3 NCs and presents its potential application in an optical detector.

Pressure-Engineered Optical and Charge Transport Properties of Mn2+/Cu2+ Codoped CsPbCl3 Perovskite Nanocrystals via Structural Progression.

In this work, compared with the corresponding pure CsPbCl3 nanocrystals (NCs) and Mn2+-doped CsPbCl3 NCs, Mn2+/Cu2+-codoped CsPbCl3 NCs exhibited improved photoluminescence (PL) and photoluminescence quantum yields (PL QYs) (57.6%), prolonged PL lifetimes (1.78 ms), and enhanced thermal endurance (523 K) as a result of efficient Mn2+ doping (3.66%) induced by the addition of CuCl2. Furthermore, we applied pressure on Mn2+/Cu2+-codoped CsPbCl3 NCs to reveal that a red shift of photoluminescence followed by a blue shift was caused by band gap evolution and related to the structural phase transition from cubic to orthorhombic. Moreover, we also found that under the preheating condition of 523 K, such phase transition exhibited obvious morphological invariance, accompanied by significantly enhanced conductivity. The pressure applied to the products treated with high temperature enlarged the electrical difference and easily intensified the interface by closer packaging. Interestingly, defect-triggered mixed ionic and electronic conducting (MIEC) was observed in annealed NCs when the applied pressure was 2.9 GPa. The pressure-dependent ionic conduction was closely related to local nanocrystal amorphization and increased deviatoric stress, as clearly described by in situ impedance spectra. Finally, retrieved products exhibited better conductivity (improved by 5-6 times) and enhanced photoelectric response than those when pressure was not applied. Our findings not only reveal the pressure-tuned optical and electrical properties via structural progression but also open up the promising exploration of more amorphous all-inorganic CsPbX3-based photoelectric applications.

Enhancing Mn Emission of CsPbCl3 Perovskite Nanocrystals via Incorporation of Rubidium Ions

Mn doped cesium lead halide perovskite nanocrystals (NCs) have potential application for white light emitting diodes. However, the emission of doped NCs is limited to trap-mediated energy transfer. The Mn doped CsPbCl3 NCs with corporation of rubidium (Rb+) ions (Mn:Cs1-xRbxPbCl3 NCs, x = 0, 0.1, 0.2, 0.3, and 0.4) were synthesized. The effect of the optical and structural properties of Mn:Cs1-xRbxPbCl3 NCs were studied by steady-state and time-resolved photoluminescence spectroscopy. The photoluminescence quantum yields and lifetimes of Mn doped CsPbCl3 NCs with different Rb+ contents were obtained. It was found that the Mn doped CsPbCl3 NCs with Rb+ content of 0.1 exhibited the highest Mn2+ emission quantum yield up to 63.18%. Interestingly, the temperature-dependent PL spectra demonstrated the enhanced Mn2+ emission of Mn doped CsPbCl3 NCs at low temperature of 80 K. The experimental result indicated the Mn2+ emission of Mn doped CsPbCl3 NCs was enhanced by incorporating Rb+ ions.

Cu doping-enhanced emission efficiency of Mn2+ in cesium lead halide perovskite nanocrystals for efficient white light-emitting diodes

Enhancing emission efficiency of Mn2+ in blue-orange dual-emitting Mn doped cesium lead halide perovskite nanocrystals (NCs) with high photoluminescence quantum yields (PL QYs) is important to fabricate high efficiency white light emitting diodes for solid state lighting. The synthesis and luminescent properties of Mn doped CsPbCl3-xBrx NCs through anion exchange of Mn and Cu co-doped CsPbCl3 NCs with PbBr2 at room temperature were studied by means of steady-state and time-resolved PL spectroscopy. The high Mn2+ PL QYs of 52–63% were obtained in the initial Mn and Cu co-doped CsPbCl3 NCs synthesized under various Mn/Pb/Cu molar ratios at 190 °C by hot injection method. A record Mn2+ PL QY up to 53% was achieved in the blue (450 nm) -orange (600 nm) dual-emitting Mn and Cu co-doped CsPbCl3-xBrx NCs through anion exchange. The enhancement of Mn emission efficiencies was attributed to reduced defect states in the doped NCs due to the incorporation of Cu ions. The efficient warm white light emitting diodes with color rendering index of 85 and luminous efficacy of 69 lm/W were fabricated by combination of the blue-orange dual-emitting Mn and Cu co-doped CsPbCl3-xBrx NCs and green emissive CsPbBr3@Cs4PbBr6 core/shell NCs. The improved color rendering index was demonstrated with increasing Mn content.

Mn2+/Yb3+ Codoped CsPbCl3 Perovskite Nanocrystals with Triple-Wavelength Emission for Luminescent Solar Concentrators.

Doping metal ions into lead halide perovskite nanocrystals (NCs) has attracted great attention over the past few years due to the emergence of novel properties relevant to optoelectronic applications. Here, the synthesis of Mn2+/Yb3+ codoped CsPbCl3 NCs through a hot‐injection technique is reported. The resulting NCs show a unique triple‐wavelength emission covering ultraviolet/blue, visible, and near‐infrared regions. By optimizing the dopant concentrations, the total photoluminescence quantum yield (PL QY) of the codoped NCs can reach ≈125.3% due to quantum cutting effects. Mechanism studies reveal the efficient energy transfer processes from host NCs to Mn2+ and Yb3+ dopant ions, as well as a possible inter‐dopant energy transfer from Mn2+ to Yb3+ ion centers. Owing to the high PL QYs and minimal reabsorption loss, the codoped perovskite NCs are demonstrated to be used as efficient emitters in luminescent solar concentrators, with greatly enhanced external optical efficiency compared to that of using solely Mn2+ doped CsPbCl3 NCs. This study presents a new model system for enriching doping chemistry studies and future applications of perovskite NCs.

Downshifting of highly energetic photons and energy transfer by Mn-doped perovskite CsPbCl3 nanocrystals in hybrid organic/silicon nanostructured solar cells

Abstract The downshifting of highly energetic photons in the ultraviolet region has the benefit of extending the spectral response and decreasing the thermalization effect in Si-related solar cells. Herein, we report low-cost hybrid organic/inorganic solar cells with minimized spectral losses with directly-deposited Mn-doped perovskite CsPbCl3 nanocrystals (NCs) on the surface of Si nanotips with PEDOT:PSS acting as the hole transporting and passivating layer. The CsPbCl3 NCs act as highly efficient radiative and non-radiative energy transfer centers. Manganese doping in CsPbCl3 NCs also drastically enhances photoluminescence quantum yields due to the charge transfer of photoinduced excitons from the CsPbCl3 host to the dopant Mn2+ centers. Finally, the Mn doped CsPbCl3 NCs enhance the cell properties and give a high power conversion efficiency of 13.48%.

Quantum yield enhancement of Mn-doped CsPbCl3 perovskite nanocrystals as luminescent down-shifting layer for CIGS solar cells

The emission and absorption properties of Mn doped CsPbCl3 NC make it ideal candidates as luminescent down shifting layer material for solar cells, However, effective Mn doping and further quantum yield improvement remains challenging. We present our modified hot injection route to obtain Mn doped CsPbCl3 nanocrystals with different morphologies and enhanced quantum yield. The samples presented were synthesized with precursor MnCl2 and PbCl2 with the ratio of 1:1, 1:2, 1:2.5 and 1:3. For samples with lower Mn doping level, the as prepared samples are uniform nanocubes with average size of 11 nm. When MnCl2 amount is increased beyond 2.5, large piece of nanosheets were found by TEM and AFM with ultrathin thickness and strong quantum confinement effect. CsPbCl3 nanocrystals with optimal Mn doping level show enhanced quantum yield of 69%. Luminescent down shifting layers prepared from Mn doped CsPbCl3 nanocrystals successfully increased short-circuit current (6.67%) and PCE (1.67%) of Cu(In,Ga)Se2 solar cell.

Triplet Energy Transfer from Perovskite Nanocrystals Mediated by Electron Transfer.

Triplet energy transfer from colloidal nanocrystals is a novel approach to sensitizing molecular triplets that are important for many applications. Recent studies suggest that this triplet transfer can be mediated by a hole transfer process when it is energetically allowed. In contrast, electron-transfer-mediated triplet transfer has not been observed yet, which is likely due to hole-trapping in typical II-VI group nanocrystals inhibiting the hole transfer step following initial electron transfer and hence disrupting a complete triplet exciton transfer. Here we report electron-transfer-mediated triplet energy transfer from CsPbCl3 and CsPbBr3 perovskite nanocrystals to surface-anchored rhodamine molecules. The mechanism was unambiguously established by ultrafast spectroscopy; control experiments using CdS nanocrystals also confirmed the role of hole-trapping in inhibiting this mechanism. The sensitized rhodamine triplets engaged in a variety of applications such as photon upconversion and singlet oxygen generation. Compared to conventional one-step triplet transfer, the electron-transfer-mediated mechanism is less demanding in terms of interfacial electronic coupling and hence is more generally implementable. Overall, this study not only establishes a complete framework of triplet energy transfer across nanocrystal/molecule interfaces but also greatly expands the scope of molecular triplet sensitization using nanocrystals.

Increasing photoluminescence yield of CsPbCl3 nanocrystals by heterovalent doping with Pr3+

CsPbCl3 perovskite nanocrystals are doped with heterovalent Pr3+ using hot-injection method. These Pr3+-doped CsPbCl3 nanocrystals exhibit a dramatically improved absolute photoluminescence quantum yield (PLQY) compared to the undoped CsPbCl3, reaching 78.9 % PLQY at 9 % Pr-substitution. The crystal structure modification upon Pr3+ doping and luminescence mechanism are investigated using conventional optical spectroscopy and synchrotron X-ray spectroscopy (i.e., X-ray absorption fine structure and X-ray excited optical luminescence). Both the Pr3+ and Cl− are found contributing to the luminescence enhancement, and their individual roles in luminescence enhancement are analyzed.

Manganese-Doping-Induced Quantum Confinement within Host Perovskite Nanocrystals through Ruddlesden-Popper Defects.

The concept of doping Mn2+ ions into II–VI semiconductor nanocrystals (NCs) was recently extended to perovskite NCs. To date, most studies on Mn2+ doped NCs focus on enhancing the emission related to the Mn2+ dopant via an energy transfer mechanism. Herein, we found that the doping of Mn2+ ions into CsPbCl3 NCs not only results in a Mn2+‐related orange emission, but also strongly influences the excitonic properties of the host NCs. We observe for the first time that Mn2+ doping leads to the formation of Ruddlesden–Popper (R.P.) defects and thus induces quantum confinement within the host NCs. We find that a slight doping with Mn2+ ions improves the size distribution of the NCs, which results in a prominent excitonic peak. However, with increasing the Mn2+ concentration, the number of R.P. planes increases leading to smaller single‐crystal domains. The thus enhanced confinement and crystal inhomogeneity cause a gradual blue shift and broadening of the excitonic transition, respectively.

Near-Unity Red Mn2+ Photoluminescence Quantum Yield of Doped CsPbCl3 Nanocrystals with Cd Incorporation.

Although Mn2+ doping in semiconductor nanocrystals (NCs) has been studied for nearly three decades, the near 100% photoluminescence (PL) quantum yield (QY) of Mn2+ emission has never been realized so far. Herein, greatly improved PL QYs of Mn2+ emissions are reported in Mn2+-doped CsPbCl3 NCs with various Mn2+ doping concentrations after CdCl2 post-treatment at room temperature. Specifically, the near-unity QY and near single-exponential decay of red Mn2+ emission peaking at 627 nm in doped CsPbCl3 NCs are obtained for the first time. The temperature dependence of steady-state and time-resolved PL spectra reveals that the CdCl2 post-treatment significantly reduces the nonradiative defect states and enhances the energy transfer from host to Mn2+ ions. Moreover, the Mn2+:CsPbCl3 NCs after CdCl2 post-treatment exhibit robust stability and high PL QYs after multipurification. The results will provide an effective route to obtain doped perovskite NCs with high performance for white lighting emitting diodes.

Stable Mn-Doped CsPbCl3 Nanocrystals inside Mesoporous Alumina Films for Display and Catalytic Applications

Doping Mn2+ in CsPbCl3 nanocrystals (NCs) has generated exciting optical properties, making it a potential candidate for illumination and display applications. Also, it opens up a way to substitute...

Enhanced luminescence of Mn doped CsPbCl3 and CsPb(Cl/Br)3 perovskite nanocrystals stabilized in glasses

Introducing of impurity ions into semiconductor nanocrystals can improve their photoluminescence quantum efficiency through energy transfer and enhance their applicability towards light-emitting devices. In this work, Mn doped CsPbCl3 and CsPbCl3-xBrx perovskite nanocrystals were prepared in glass through melt-quenching and subsequent thermal treatment. Both Mn doping concentration and thermal treatment conditions affected the growth and resultant band edge emission of perovskite nanocrystals, enabling tunable photoluminescence ranging from UV to blue. In addition to UV-blue band edge emission from these Mn-doped perovskite nanocrystals, red emission from Mn ions was activated through efficient energy transfer from perovskite nanocrystals. Intensity ratio between the band edge emission of perovskite nanocrystals and red emission of Mn ions was also tunable by varying the Mn doping concentration and heat-treatment conditions, covering a wider color gamut. Along with the good chemical and mechanical properties of glass matrix, these Mn-doped cesium lead halide perovskite nanocrystal embedded glasses have potentials for applications in light emitting devices.

Ambient Condition Mg2+ Doping Producing Highly Luminescent Green- and Violet-Emitting Perovskite Nanocrystals with Reduced Toxicity and Enhanced Stability.

The lack of long-term stability, the presence of toxic lead, and a low photoluminescence (PL) efficiency are the major obstacles to the commercialization of lead-halide perovskite-based optoelectronic and photovoltaic devices. Herein we report a facile ambient condition doping protocol that addresses all three issues of the CsPbX3 perovskite nanocrystals (NCs) to a substantial extent. We show that the room-temperature treatment of these NCs with MgX2 results in the partial (18-23%) replacement of toxic lead, enhances the PL quantum yield of green-emitting CsPbBr3 (to ∼100% from ∼51%) and violet-emitting CsPbCl3 NCs (to ∼79% from ∼1%), and improves the stability under ambient conditions and in the presence of light and a polar solvent. Ultrafast pump-probe and temperature-dependent PL studies reveal that curing of the intrinsic structural disorder, introduction of some shallow energy levels close to the conduction band edge, and effective passivation of the halide deficiency contribute to the improved properties of the doped systems.

Role of Solid-State Miscibility during Anion Exchange in Cesium Lead Halide Nanocrystals Probed by Single-Particle Fluorescence.

In this Letter, we used fluorescence microscopy to image the reversible transformation of individual CsPbCl3 nanocrystals to CsPbBr3, which enables us to quantify heterogeneity in reactivity among hundreds of nanocrystals prepared within the same batch. We observed a wide distribution of waiting times for individual nanocrystals to react as has been seen previously for cation exchange and ion intercalation. However, a significant difference for this reaction is that the switching times for changes in fluorescence intensity are dependent on the concentration of substitutional halide ions in solution (i.e., Br- or Cl-). On the basis of the high solid-state miscibility between CsPbCl3 and CsPbBr3, we develop a model in which the activation energy for anion exchange depends on the density of exchanged ions in the nanocrystal. The heterogeneity in reaction kinetics observed among individual nanocrystals limits the compositional uniformity that can be achieved in luminescent CsPbCl3-xBrx nanocrystals prepared by anion exchange.

Synthesis of monodisperse water-stable surface Pb-rich CsPbCl3 nanocrystals for efficient photocatalytic CO2 reduction.

Surface Pb-rich lead halide (CsPbCl3) perovskite nanocrystals (NCs) with high stability and monodispersity in water have been synthesized using a general and convenient liquid-solid interpenetration (LSI) method. In this process, water molecules permeate into the solid CsPbCl3 NC layers and slowly dissolve the Cs+ and Cl- ions on the surface of CsPbCl3 NCs. The Cs+ and Cl- ions in water inhibit the decomposition rate of CsPbCl3 NCs, inducing surface Pb-rich layers. The surface Pb-rich structure increases the photoluminescence (PL) lifetimes and improves the photocatalytic performances of lead halide perovskite NCs. Under simulated solar irradiation, the largest rate of CO2 photoreduction from surface Pb-rich Ni-doped CsPbCl3 NCs reaches up to 169.37 μmol g-1 h-1. This study provides an effective general strategy to design stable lead halide perovskite quantum dots (QDs) for their wide applications.