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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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Light-Stimulated Synaptic Transistors Fabricated by a Facile Solution Process Based on Inorganic Perovskite Quantum Dots and Organic Semiconductors
摘要： Implementation of artificial intelligent systems with light-stimulated synaptic emulators may enhance computational speed by providing devices with high bandwidth, low power computation requirements, and low crosstalk. One of the key challenges is to develop light-stimulated devices that can response to light signals in a neuron-/synapse-like fashion. A simple and effective solution process to fabricate light-stimulated synaptic transistors (LSSTs) based on inorganic halide perovskite quantum dots (IHP QDs) and organic semiconductors (OSCs) is reported. Blending IHP QDs and OSCs not only improves the charge separation efficiency of the photoexcited charges, but also induces delayed decay of the photocurrent in the IHP QDs/OSCs hybrid film. The enhanced charge separation efficiency results in high photoresponsivity, while the induced delayed decay of the photocurrent is critical to achieving light-stimulating devices with a memory effect, which are important for achieving high synaptic performance. The LSSTs can respond to light signals in a highly neuron-/synapse-like fashion. Both short-term and long-term synaptic behaviors have been realized, which may lay the foundation for the future implementation of artificial intelligent systems that are enabled by light signals. More significantly, LSSTs are fabricated by a facile solution process which can be easily applied to large-scale samples.
关键词： light-stimulated synaptic transistors,solution process,organic semiconductors,blended materials,inorganic halide perovskite quantum dots
更新于2025-11-19 16:56:42
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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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Suppression of Iodide Ions Migration via Sb2S3 interfacial Modification for stable Inorganic Perovskite Solar Cells
摘要： In mixed halide perovskite, the halide phase segregation is commonly observed due to halide ions migration, which causes severe stability issues in perovskite devices. Here, we directly revealed the iodide-migration process via potentiostatic treatment in CsPbIBr2 perovskite. The absence of iodide ions was reduced significantly via Sb2S3 interfacial modification. We further employed the DFT calculation to optimize the geometry positions at the perovskite interface and radial distribution functions (RDF) to analyze the atom perturbation. The simulation yielded a slight distortion of perovskite lattice at the interface of Sb2S3-CsPbIBr2 and iodide ions fluctuation was reduced due to the decrease of halide vacancies. In addition, the thermally stimulated current was calculated to evaluate the defects density in the modified perovskite device. Due to the Sb2S3 interaction with perovskite, the device became stable against humidity and maintained photoactive over 400 h. The champion efficiency of 9.31% with 26.31% improvement was obtained in modified CsPbIBr2 perovskite solar cells.
关键词： stability,The mixed halide perovskite,Sb2S3,DFT,iodide ions migration
更新于2025-11-14 15:15:56
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Fascinating Physical Properties of 2D Hybrid Perovskite [(NH3)(CH2)7(NH3)]CuClxBr4?x, x?=?0, 2 and 4
摘要： The 2-D organic–inorganic hybrid perovskites of the formula [(NH3)(CH2)7(NH3)]CuClxBr4?x, x = 0, 2 and 4 were prepared by slow evaporation from ethanolic solution in stoichiometric ratio 1:1 (organic/inorganic). Microchemical analysis and x-ray diffraction (XRD) were used to confirm the formation of the presently investigated hybrids. Differential scanning calorimetry (DSC) indicated order–disorder transitions at T1 = 357 K, T2 = 388 K, and T3 = 398 K for x = 0, 2 and 4 of the three heptane diammonium Cu hybrid perovskites, respectively. These transitions are in good agreement with the electrical permittivity results at different frequencies and temperatures. Optical properties and estimated band gap energy reveal that the band gap energy decreases sharply with replacement of Cl ion by Br ion where the band gap energy of [(NH3)(CH2)7(NH3)]CuBr4, x = 0 (denoted 2C7CuBr) is 1.6 eV (brown color) and for [(NH3)(CH2)7(NH3)]CuCl4, x = 4 (denoted 2C7CuCl) is 2.6 eV (yellow color). The differential magnetic susceptibility of 2C7CuBr in the temperature range 80–300 K indicates the effective magnetic moment μeff = 2.05 BM.
关键词： 2D hybrid perovskite,optical properties of halide perovskite,phase transition,magnetic properties of Cu perovskite
更新于2025-09-23 15:23:52
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Spectrally Resolved Ultrafast Exciton Transfer in Mixed Perovskite Quantum Wells
摘要： Solution-processed perovskite quantum wells have been used to fabricate increasingly efficient and stable optoelectronic devices. Little is known about the dynamics of photogenerated excitons in perovskite quantum wells within the first few hundred femtoseconds – a crucial timescale on which energy and charge transfer processes may compete. Here we use ultrafast transient absorption and two-dimensional electronic spectroscopy to clarify the movement of excitons and charges in reduced-dimensional perovskite solids. We report excitonic funneling from strongly to weakly confined perovskite quantum wells within 150 fs, facilitated by strong spectral overlap and orientational alignment among neighboring wells. This energy transfer happens on timescales orders of magnitude faster than charge transfer, which we find to occur instead over 10 - 100s of picoseconds. Simulations of both F?rster-type interwell exciton transfer and free carrier charge transfer are in agreement with these experimental findings, with theoretical exciton transfer calculated to occur in 100s of fs.
关键词： energy transfer,Carrier,metal halide perovskite,two-dimensional electronic spectroscopy,layered perovskite,dynamics
更新于2025-09-23 15:23:52
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Stark Effect and Environment-Induced Modulation of Emission in Single Halide Perovskite Nanocrystals
摘要： Organic-inorganic halide perovskites have emerged as promising materials for next generation solar cells. In nanostructured form also, these materials are excellent candidates for optoelectronic applications such as lasers and light emitting diodes for displays and lighting. While great progress has been achieved so far in optimizing the intrinsic photophysical properties of perovskite nanocrystals (NCs), in working opto-electronic devices external factors, such as the effects of conducting environment and of the applied electric field on exciton generation and photon emission have been largely unexplored. Here, we use NCs of the all-inorganic perovskite CsPbBr3 dispersed polyvinyl carbazole, a hole-conductor, and in polymethyl methacrylate, an insulator, to examine the effects of applied electric field and conductivity of the matrix on the perovskite photophysics at single-particle level. We found that the conducting environment causes a significant decrease of photoluminescence (PL) brightness of individual NCs due the appearance of intermediate-intensity emitting states with significantly shortened lifetime. Applied electric field has a similar effect and, in addition, causes a non-linear spectral-shift of the PL maxima, a combination of linear and quadratic Stark effect caused by environment-induced polarity and field-related polarizability. The environment and electric field effects are explained by ionization of the NCs through hole transfer and emission of the resulting negatively-charged excitons.
关键词： ionization,halide perovskite nanocrystals,single-particle spectroscopy,Stark effect,blinking
更新于2025-09-23 15:23:52
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Alternative Type 2D-3D Lead Halide Perovskite with Inorganic Sodium Ions as Spacer for High Performance Light Emitting Diodes
摘要： Two-dimensional (2D) lead halide perovskites with long-chain ammonium halides display high photoluminescence quantum yield (PLQY), due to their size and dielectric confinement, which promise a high efficiency and low-cost light emitting diode (LED). However, the presence of insulating organic long-chain spacer cation (L) dramatically deteriorates the charge transport properties along the out-of-plane nanoplatelet direction or adjacent nanocrystals, which would limit the LED device performance. In order to overcome this issue, we successfully incorporate small alkaline ions such as sodium (Na+) to replace long organic molecule. Grazing incident X-ray diffraction (GIXRD) measurements verify the 2D layered formation with preferential crystallite orientation. In addition, the incorporated sodium salt also generates amorphous sodium lead bromide (NaPbBr3) in perovskite as spacers to form nanocrystal-like halide perovskite film. PLQY is dramatically improved in the sodium incorporated film associating with enhanced PL lifetime. With incorporating small concentration of an organic additive, this 2D-3D perovskite can achieve a compact and uniform film. Therefore, a 2D-3D perovskite achieves a high external quantum efficiency (EQE) of 15.9% with good operational stability. Our work develops a type of 2D-3D halide perovskite with various inorganic ions as spacers for high performance of promising optoelectronic devices.
关键词： two-dimensional,alkaline halide,perovskite,dielectric confinement,light-emitting diode
更新于2025-09-23 15:23:52
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Unusual pressure-induced electronic structure evolution in organometal halide perovskite predicted from first-principles
摘要： Pressure has been demonstrated to be an effective parameter to alter the atomic and electronic structures of materials. By using the first-principles calculations based on density functional theory (DFT), we systematically investigated the changes in the atomic and electronic structures of the cubic MAPbI3 phase under pressures. It is found that the band gap of the compressed cubic MAPbI3 structure exhibits a remarkable redshift to 1.114/1.380 eV in DFT/HSE-SOC calculation under a mild pressure of 2.772 GPa, and subsequently shows a widening at higher pressures until ~20 GPa. As the pressure further increases, the band gap closes at ~80 GPa. Detailed structural and electronic characteristic analyses indicate that the band gap of the cubic MAPbI3 structure is determined by two competing effects: the lattice contraction decreases its band gap while the PbI6 octahedral tilting increases it. Given that, pressure can be a powerful tool to help understanding the optoelectronic properties of perovskite materials.
关键词： Density functional theory,Pressure,Organometal halide perovskite,Electronic structure
更新于2025-09-23 15:23:52
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Semimetallicity and Negative Differential Resistance from Hybrid Halide Perovskite Nanowires
摘要： In the rapidly progressing field of organometal halide perovskites, the dimensional reduction can open up new opportunities for device applications. Herein, taking the recently synthesized trimethylsulfonium lead triiodide (CH3)3SPbI3 perovskite as a representative example, first-principles calculations are carried out and the nanostructuring and device application of halide perovskite nanowires are studied. It is found that the 1D (CH3)3SPbI3 structure is structurally stable, and the electronic structures of higher-dimensional forms are robustly determined at the 1D level. Remarkably, due to the face-sharing [PbI6] octahedral atomic structure, the organic ligand-removed 1D PbI3 frameworks are also found to be stable. Moreover, the PbI3 columns avoid the Peierls distortion and assume a semimetallic character, contradicting the conventional assumption of semiconducting metal-halogen inorganic frameworks. Adopting the bundled nanowire junctions consisting of (CH3)3SPbI3 channels with sub-5 nm dimensions sandwiched between PbI3 electrodes, high current densities and large room-temperature negative differential resistance (NDR) are finally obtained. It will be emphasized that the NDR originates from the combination of the near-Ohmic character of PbI3-(CH3)3SPbI3 contacts and a novel NDR mechanism that involves the quantum-mechanical hybridization between channel and electrode states. This work demonstrates the great potential of low-dimensional hybrid perovskites toward advanced electronic devices beyond actively pursued photonic applications.
关键词： semimetals,halide perovskite nanowires,first-principles calculations,negative differential resistance
更新于2025-09-23 15:22:29