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Post-synthesis phase and shape evolution of CsPbBr3 colloidal nanocrystals: The role of ligands
摘要： The surface chemistry of colloidal cesium lead bromide (CsPbBr3) nanocrystals is decisive in determining the stability and the final morphology of this class of materials, characterized by ionic structure and a high defect tolerance factor. Here, the high sensitivity of purified colloidal nanocubes of CsPbBr3 to diverse environmental condition (solvent dilution, ageing, ligands post synthetic treatment) in ambient atmosphere is investigated by means of a comprehensive morphological (electron microscopy), structural (θ/2θ X-ray diffraction (XRD) and grazing incidence wide angle scattering (GIWAXS)), and spectroscopic chemical (1H nuclear magnetic resonance (NMR), nuclear Overhauser effect spectroscopy (NOESY), absorption and emission spectroscopy) characterization. The aging and solvent dilution contribute to modify the nanocrystal morphology, due to a modification of the ligand dynamic. Moreover, we establish the ability of aliphatic carboxylic acids and alkyl amines ligands to induce, even in a post preparative process at room temperature, structural, morphological and spectroscopic variations. Upon post synthesis alkyl amine addition, in particular of oleyl amine and octyl amine, the highly green emitting CsPbBr3 nanocubes effectively turn into one-dimensional (1D) thin tetragonal nanowires or lead halide deficient rhombohedral zero-dimensional (0D) Cs4PbBr6 structures with a complete loss of fluorescence. The addition of an alkyl carboxylic acid, as oleic and nonanoic acid, produces the transformation of nanocubes into still emitting orthorombic two-dimensional (2D) nanoplates. The acid/base equilibrium between the native and added ligands, the adsorbed/free ligands dynamic in solution and the ligand solubility in non-polar solvent contribute to render CsPbBr3 particularly sensitive to environmental and processing conditions and, therefore prone to undergo to structural, morphological and, hence spectroscopic, transformations.
关键词： lead halide perovskite nanocrystals,surface chemistry,ligands equilibria,long term stability
更新于2025-11-21 11:01:37
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Direct Hot-Injection Synthesis of Lead Halide Perovskite Nanocubes in Acrylic Monomers for Ultrastable and Bright Nanocrystal–Polymer Composite Films
摘要： In recent years, lead halide perovskite nanocrystals (NCs) have attracted significant attention in both fundamental research and commercial applications due to their excellent optical and optoelectrical properties. However, the protective ligands on the surface of the perovskites NCs could be easily removed after the tedious process of centrifugation, separation, and dispersion, which greatly hampers their stability against light, heat, moisture, and oxygen and limits their practical applications. Here we report a new post-processing-free strategy (i.e., without centrifugation, separation, and dispersion process) of using an UV-polymerizable acrylic monomer of lauryl methacrylate (LMA) as the solvent to synthesize CsPbBr3 NCs, and then adding polyester polyurethane acrylates oligomer, monomer (IBOA) and initiator for directly UV polymerization to fabricate NC-polymer composite films. These films exhibited an improved photoluminescence quantum yield (85-90%) than classic NC-film (40-50%), which were processed using octadecene (ODE) as the solvent for NC synthesis and post-processed for UV polymerization. Significantly, the as-fabricated films by post-processing-free strategy exhibited excellent photostability against strong Xe lamp illumination; while the other films using classic methods were quickly photo-degraded. Meanwhile, these NC-polymer composite films showed good stability against moisture and heating when aging in water at 50oC for over 200 hours. These films, along with K2SiF6:Mn4+ (KSF) phosphor emitters, were used as downconverters for blue LEDs in liquid crystal displays with a wide color gamut of 115% in the International Commission on Illumination (CIE) 1931 color space. This work provides a facile and effective strategy for the preparation of ultrastable and bright color-conversion NC films for the development of the next-generation wide color gamut displays.
关键词： display backlight,lead halide perovskite,colloidal nanocrystals,color-conversion optical films,photostability
更新于2025-11-14 17:03:37
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Ultrafast Interfacial Charge Transfer of Cesium Lead Halide Perovskite Films CsPbX3 (X = Cl, Br, I) with Different Halogen Mixing
摘要： Understanding the interfacial charge transfer of the photoinduced transients of all-inorganic cesium lead halide perovskites (CsPbX3; X = Cl, Br, I) is critical for their photovoltaic applications. Ultrafast dynamics can provide comprehensive information about the transient behavior of the carriers and their transfer mechanism in the materials. In this work, the interfacial charge transfer of CsPbX3 films assembled with TiO2 with different halogen doping ratios was studied using femtosecond transient absorption (TA) spectroscopy combined with global analysis. Four subsequent decay processes after photoexcitation were obtained, including hot carrier cooling, free exciton forming, electron transfer, and charge recombination. The results indicate that the time constant of the interfacial electron transfer varies with the location of the trap state of these perovskites and the relative energy of CBs in the perovskite and TiO2 and that the time constant of the charge recombination can be attributed to the electron–hole interactions. These interpretations are supported by calculations based on first-principles density functional theory (DFT). Greater iodine doping in such perovskite CsPbX3/TiO2 systems increases the time constants of the electron transfer and charge recombination, which suggests that all-inorganic perovskite CsPbX3 with a high iodine content is favorable for improving the power conversion efficiency of solar cells.
关键词： cesium lead halide perovskite,transient absorption,global analysis,interfacial charge transfer
更新于2025-09-23 15:21:01
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One-step Co-evaporation of All-Inorganic Perovskite Thin Films with Room Temperature Ultralow Amplified Spontaneous Emission Threshold and Air-stability
摘要： Inorganic cesium lead halide perovskite has been successfully applied in optoelectronic field due to its remarkable optical gain properties. Unfortunately, conventional solution-processed CsPbX3 films suffer unavoidable pinhole defects and poor surface morphology, severely limiting their performance on amplified spontaneous emission (ASE) and lasing application. Herein, a dual-source thermal evaporation approach is explored in our work to achieve a uniform and high-coverage CsPbX3 polycrystalline thin film. It is found that the one-step co-evaporated CsPbBr3 (OC-CsPbBr3) thin films without post-annealing exhibit an ultralow ASE threshold of ~ 3.3 μJ/cm2 and gain coefficient above 300 cm-1. The coexistence of cubic and orthorhombic phases in this materials naturally form an energy cascade for the exciton transfer process, which enables rapid accumulation of excitons. Stable ASE intensity without degradation for at least 7 hours is also realized from OC-CsPbBr3 thin films under continuous excitation, which is superior to that in the solution-processed CsPbBr3 thin film. Notably, a Fabry-Perot (F-P) cavity laser based on the OC-CsPbBr3 thin film is first achieved, featuring an ultralow lasing threshold (1.7 μJ/cm2) and directional output (beam divergence of ~ 3.8°). This work highlights the noteworthy optical properties of OC-CsPbBr3 thin films, leading to potential available applications in the integrated optoelectronic chips.
关键词： amplified spontaneous emission,Cesium lead halide perovskite,vapor deposition,long-term stability,thin films
更新于2025-09-23 15:21:01
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Recent Progress of Strong Exciton-Photon Coupling in Lead Halide Perovskites
摘要： The semiconductor exciton–polariton, arising from the strong coupling between excitons and confined cavity photon modes, is not only of fundamental importance in macroscopic quantum effects but also has wide application prospects in ultralow-threshold polariton lasers, slowing-light devices, and quantum light sources. Very recently, metallic halide perovskites have been considered as a great candidate for exciton–polariton devices owing to their low-cost fabrication, large exciton oscillator strength, and binding energy. Herein, the latest progress in exciton–polaritons and polariton lasers of perovskites are reviewed. Polaritons in planar and nanowires Fabry–Pérot microcavities are discussed with particular reference to material and photophysics. Finally, a perspective on the remaining challenges in perovskite polaritons research is given.
关键词： exciton–polariton,low threshold laser,lead halide perovskite,optical microcavity,strong light–matter interaction
更新于2025-09-23 15:21:01
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On the determination of absorption cross section of colloidal lead halide perovskite quantum dots
摘要： The absorption cross section of lead halide perovskite nanocrystals is important for understanding their photophysical properties, especially those depending on the density of photoexcited charge carriers. Despite its importance, there are large discrepancies among the reported absorption cross section values determined employing different methods. Here, we measured the absorption cross section of CsPbBr3 quantum dots (QDs) of varying sizes using elemental analysis and transient absorption (TA) saturation methods and compared with the previously reported values determined from elemental analysis and transient photoluminescence (PL) saturation methods. A careful comparison indicates that the reliable absorption cross section of lead halide perovskite QDs is obtained from both elemental analysis and TA saturation methods, while many previously reported values determined from the PL saturation method underestimate the absorption cross section.
关键词： quantum dots,absorption cross section,photoluminescence,transient absorption,lead halide perovskite
更新于2025-09-23 15:19:57
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Strong Spin-Selective Optical Stark Effect in Lead Halide Perovskite Quantum Dots
摘要： The optical Stark effect (OSE) stems from a coherent, nonlinear interaction between a transition and a non-resonant light field, which usually causes a blue-shift of the transition energy. This shift can be understood using the picture of so-called photon-dressed states or Floquet states. The perturbation induced by a light filed which is periodical in time results in a series of quasi-static Floquet eigenstates periodically spaced in units of the photon energy. The repulsion (hybridization) between the Floquet and equilibrium states causes a blueshift of the transition between the equilibrium states, as schematically shown in Fig. 1a. The OSE effect is intrinsically helicity-selective, that is, a left circularly polarized light couples only to the |0> to |+1> but not the |0> to |-1> transition and vice versa (the number in the ket is the azimuthal quantum number of the total angular momentum). Experimentally, the OSE can be conveniently observed using circularly polarized transient absorption (TA) spectroscopy. With a co-circularly polarized pump-probe configuration, the probe pulse measures a blue-shifted transition in the duration of the pump pulse and a derivative-like difference spectrum (with respect to the unpumped spectrum) can be detected (Fig. 1b), whereas with a counter-circularly polarized configuration nothing can be detected if multi-photon absorption is negligible.
关键词： transient absorption spectroscopy,optical Stark effect,spin-selective,lead halide perovskite,quantum dots
更新于2025-09-23 15:19:57
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Controllable synthesis of all inorganic lead halide perovskite nanocrystals and white light-emitting diodes based on CsPbBr3 nanocrystals
摘要： The colloidal cesium lead halide perovskite nanocrystals (NCs) have attracted much attention over the past five years as a promising class of material with potential application in wide-color-gamut backlight display because of their high photoluminescence quantum yield (PLQY) and narrow-band emission (full-width at half-maximum, FWHM < 35 nm). To controllably synthesize perovskite NCs, the effects of reaction temperature and reaction time on structure, morphology, particle size and photoluminescence (PL) properties of the NCs were systematically investigated in this article. Based on these results, the formation kinetics of the perovskite NCs was analyzed and disclosed in further. Finally, a white light-emitting diode (WLED) was prepared by using synthesized CsPbBr3 NCs and K2SiF6:Mn4+ phosphors as the color converters. The WLED exhibits the bright white emission with a CIE chromaticity coordinate of (0.389, 0.376) and a wide color gamut of 123% of NTSC, indicating a potential application in the field of wide color gamut displays in the future.
关键词： Cesium lead halide perovskite,white light-emitting diodes,photoluminescent,hot-injection method,nanocrystals
更新于2025-09-23 15:19:57
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Exploring the surface chemistry of cesium lead halide perovskite nanocrystals
摘要： Colloidal nanocrystals (NCs) of cesium lead halide perovskites (CsPbX3, X = Cl, Br or I) are emerging as an exciting class of optoelectronic materials, but the retention of their colloidal and structural integrity during isolation, purification and handling still represents a critical issue. The impelling questions concerning their intrinsic chemical instability are connected to the dynamic nature of the bonding between the inorganic surface and the long-chain capping ligands. However, the key aspects of CsPbX3's surface chemistry that directly impact their stability remain elusive. In this contribution, we provide an in-depth investigation of the surface properties of differently composed CsPbX3 NCs, prepared by traditional hot-injection methods. The study, mainly relying on solution NMR spectroscopy, is backed up by elemental analysis as well as morphological, structural and optical investigations. We ascertained that the nature of the ligand adsorption/desorption processes at the NC surface is dependent on its elemental composition, thus explaining the origin of the instability afflicting CsPbI3 NCs. We also evaluated the effect of NC purification as well as of the degradation pathways involving the organic shell on the surface chemistry of CsPbX3 NCs. This study paves the way for new post-functionalization strategies for this promising class of nanomaterials.
关键词： surface chemistry,colloidal stability,degradation pathways,cesium lead halide perovskite nanocrystals,purification,ligand adsorption/desorption,NMR spectroscopy
更新于2025-09-19 17:15:36
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Embedded two dimensional perovskite nanoplatelets with air-stable luminescence
摘要： Two-dimensional (2D) perovskites represent a class of promising nanostructures for optoelectronic applications owing to their giant oscillator strength transition of excitons and high luminescence. However, major challenges lie in the surface ligand engineering and ambient stability. Here we show that air-stable quasi-2D CsPbBr3 nanoplatelets (NPLs) can be formed in the matrix of Cs4PbBr6 nanosheets by reducing the thickness of Cs4PbBr6 to ~7.6 nm, the scale comparable to the exciton Bohr radius of CsPbBr3. The 2D behavior of excitons is evidenced by the linear increase of radiative lifetime with increasing temperature. Moreover, the wide bandgap Cs4PbBr6 plays roles of surface passivation and protection, which leads to good photoluminescence properties without photo-bleaching effect and with ambient stability for over one month. Our work demonstrates a unique quasi-2D heterostructure of perovskite nanomaterials which may either serve as a workbench for studying the exciton recombination dynamics or find application in high performance optoelectronic devices.
关键词： two dimensional exciton,heterostructure,luminescence,lead halide perovskite
更新于2025-09-19 17:15:36