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Giant exchange bias in the single-layered Ruddlesden-Popper perovskite
摘要： Exchange bias (EB) as large as ～5.5 kOe is observed in SrLaCo0.5Mn0.5O4, which is the highest ever found in any layered transition-metal oxides including Ruddlesden-Popper series. Neutron-diffraction measurement rules out long-range magnetic ordering and together with dc magnetic measurements suggests formation of short-range magnetic domains. Ac magnetic susceptibility, magnetic memory effect, and magnetic training effect con?rm the system to be a cluster spin glass. By carrying out density functional calculations on several model con?gurations, we propose that EB is originated at the boundary between Mn-rich antiferromagnetic and Co-rich ferromagnetic domains at the subnanoscale. Reversal of magnetization axis on the Co side alters the magnetic coupling between the interfacial Mn and Co spins, which leads to EB. Our analysis infers that the presence of competing magnetic interactions is suf?cient to induce exchange bias and thereby a wide range of materials exhibiting giant EB can be engineered for designing novel magnetic memory devices.
关键词： Ruddlesden-Popper perovskite,Exchange bias,cluster spin glass,magnetic memory devices
更新于2025-09-23 15:21:21
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Tin halide perovskite films made of highly oriented 2D crystals enable more efficient and stable lead-free perovskite solar cells
摘要： Low toxicity and an ideal energy bandgap make 2D Ruddlesden-Popper tin-based halide perovskites a promising photovoltaic material. However, the disordered crystal orientation and the oxidation of Sn2+ to Sn4+ still need to be addressed. Here, we demonstrate that the annealing of FASnI3 assisted by phenyl ethyl ammonium chloride enables the formation of more ordered 2D tin-based perovskite crystals oriented vertically. We use in-situ synchrotron-based grazing incident X-ray diffraction (GIXRD) to correlate the higher crystal orientation to the better device performance. We measured a maximum power conversion efficiency of >9%. Furthermore, we demonstrate that the phenyl ethyl ammonium chloride acts as a barrier layer at the surface of the crystals protecting the tin from the oxidation. Hence, this work paves the way for more efficient and stable lead-free perovskite solar cells.
关键词： phenyl ethyl ammonium chloride,photovoltaic material,crystal orientation,lead-free perovskite solar cells,oxidation of Sn2+,2D Ruddlesden-Popper tin-based halide perovskites,power conversion efficiency
更新于2025-09-23 15:21:01
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General Synthesis Principles for Ruddlesden-Popper Hybrid Perovskite Halides from a Dynamic Equilibrium
摘要： Two-dimensional (2D) Ruddlesden-Popper hybrid perovskites are a homologous series of compounds with the formula A’2An–1BnX3n+1 (A’ = bulky organic cation; A = small organic cation; B = Pb2+ or Sn2+, X = Cl–, Br–, I–; n is an integer) composed of inorganic octahedra layers separated by organic spacer cations. The octahedral layer thickness is modified by the stoichiometry of the A site cation, but limited methods exist for controlled and discriminating synthesis for all compositions. We report a general synthesis method and its principles that yield phase-pure 2D hybrid perovskites; the chemistry operates within a dynamic equilibrium established by the molar solubility of the compounds within the homologous series. A solvent-antisolvent (HI-acetic acid) pair and the common-ion effect provide selective control over the molar solubility to precipitate phase-pure compounds, as is supported by simple and predictive calculations. Here, this approach is demonstrated in detail with A’ = n-butylammonium, A = methylammonium, and n ≤ 3 and is applied to the synthesis and discovery of materials with other bulky ammonium cations (e.g., iso-butylammonium and benzylammonium).
关键词： dynamic equilibrium,Ruddlesden-Popper,molar solubility,common-ion effect,hybrid perovskites,solvent-antisolvent,synthesis
更新于2025-09-23 15:21:01
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Layered Ruddlesdena??Popper Perovskites with Various Thicknesses for Stable Solid-State Solar Cells
摘要： The present research comes up with optimizing the layers thickness of a Ruddlesden–Popper perovskite with the general formula of (S0.97S'0.03)2[Cs0.05(FA0.097MA0.03)0.95]n – 1Pbn(I0.97Br0.03)3n + 1 for efficient, stable solar cell applications. Such a triple-cation quasi-two-dimensional (2D) structure simultaneously contains two spacers, namely 5-ammonium valeric acid iodide (S) and tetra-n-octylammonium bromide (S'). Systematic studies showed that morphology, crystal structure, optical properties, photovoltaic performance, and internal resistances of this compound depended upon the value of the n integer. Field emission scanning electron microscopy set forth that the deposited films were composed of various morphologies depending on the n value. An increase in the n value resulted in improving the light absorption, reducing the band gap energy, and blue-shifting the photoluminescence peak. So as to fabricate solar cells, CuInS2 nanoparticles were employed as a novel hole-transporting material. The device based on the film having n = 4 value showed the highest power conversion efficiency of 10.2%. Electrochemical impedance spectroscopy demonstrated that the improved performance of this cell was mainly thanks to its low series resistance (11.68 Ω), and long electron lifetime (8.05 μs) as compared to all the fabricated cells. Moreover, this cell displayed a maximum external quantum efficiency of 82% among all the devices. The un-encapsulated solar cells showed that the output reduction directly depended on the n value so that the cell based on the n = 4 reached 82% of its initial power over 2500 h in ambient conditions.
关键词： tetra-n-octylammonium bromide,Ruddlesden–Popper structure,2D triple-cation perovskite,solar cells
更新于2025-09-23 15:21:01
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Energetics and Energy Loss in 2D Ruddlesdena??Popper Perovskite Solar Cells
摘要： 2D Ruddlesden–Popper perovskites (RPPs) are emerging as potential challengers to their 3D counterpart due to superior stability and competitive efficiency. However, the fundamental questions on energetics of the 2D RPPs are not well understood. Here, the energetics at (PEA)2(MA)n?1PbnI3n+1/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) interfaces with varying n values of 1, 3, 5, 40, and ∞ are systematically investigated. It is found that n–n junctions form at the 2D RPP interfaces (n = 3, 5, and 40), instead of p–n junctions in the pure 2D and 3D scenarios (n = 1 and ∞). The potential gradient across phenethylammonium iodide ligands that significantly decreases surface work function, promotes separation of the photogenerated charge carriers with electron transferring from perovskite crystal to ligand at the interface, reducing charge recombination, which contributes to the smallest energy loss and the highest open-circuit voltage (Voc) in the perovskite solar cells (PSCs) based on the 2D RPP (n = 5)/PCBM. The mechanism is further verified by inserting a thin 2D RPP capping layer between pure 3D perovskite and PCBM in PSCs, causing the Voc to evidently increase by 94 mV. Capacitance–voltage measurements with Mott–Schottky analysis demonstrate that such Voc improvement is attributed to the enhanced potential at the interface.
关键词： energy loss,2D Ruddlesden–Popper perovskites,open-circuit voltage,perovskite solar cells,energetics
更新于2025-09-23 15:21:01
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Quantum dots of two-dimensional Ruddlesdena??Popper organica??inorganic hybrid perovskite with high optical limiting properties
摘要： Hybrid perovskites have been investigated for various potential applications because of their tunable optical properties. In this paper, we report the synthesis of quantum dots (QDs) of two-dimensional (2D) Ruddlesden–Popper (RP) hybrid perovskite using a top-down approach. The QDs of the developed 2D RP perovskite exhibit high and sharp photoluminescence in the ultraviolet region. The sharp peak in the absorption spectrum and the intense photoluminescence in the ultraviolet region indicate strong quantum confinement in these particles, which is further confirmed by x-ray photoelectron spectroscopy. These QDs show superior nonlinear optical scattering and absorption properties with the optical z-scan technique and strong nonlinear absorption property with the photoacoustic z-scan technique. Evaluating the nonlinear optical properties using two complementary techniques provides a deeper understanding of the nonlinear mechanism involved in the optical limiting process. The two-photon absorption coefficient obtained by optical z-scan is 7.2 × 102 cm/GW, which is larger than that of most perovskite nanocrystals and nanosheets. Our studies, therefore, reveal a new class of material, 2D RP perovskite QDs, which show important nonlinear properties that are important for optical limiting applications.
关键词： Ruddlesden–Popper perovskite,optical limiting,nonlinear optical properties,Quantum dots,two-photon absorption
更新于2025-09-23 15:21:01
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Remote Phononic Effects in Epitaxial Ruddlesden-Popper Halide Perovskites
摘要： Despite their weak nature, van der Waals (vdW) interactions have been shown to effectively control the optoelectronic and vibrational properties of layered materials. However, how vdW effects exist in Ruddlesden-Popper layered halide perovskites remains unclear. Here we reveal the role of interlayer vdW force in Ruddlesden-Popper perovskite in regulating phase transition kinetics and carrier dynamics, based on high-quality epitaxial single crystalline (C4H9NH3)2PbI4 flakes with controlled dimensions. Both substrate-perovskite epitaxial interaction and interlayer vdW interaction play significant roles in suppressing the structural phase transition. With reducing flake thickness from ~100 nm to ~20 nm, electron-phonon coupling strength decreases by ~30%, suggesting the ineffectiveness of phonon confinement of the natural quantum wells. Therefore, the conventional understanding that vdW perovskite is equivalent to a multiple quantum well has to be substantially amended due to significant nonlocal phononic effects in the layered crystal where intralayer interaction is not drastically different from the interlayer force.
关键词： phase transition,electron-phonon coupling,Ruddlesden-Popper perovskites,epitaxial growth,van der Waals interactions
更新于2025-09-23 15:21:01
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Thermal stability study of transition metal perovskite sulfides
摘要： Transition metal perovskite chalcogenides, a class of materials with rich tunability in functionalities, are gaining increased attention as candidate materials for renewable energy applications. Perovskite oxides are considered excellent n-type thermoelectric materials. Compared to oxide counterparts, we expect the chalcogenides to possess more favorable thermoelectric properties such as lower lattice thermal conductivity and smaller band gap, making them promising material candidates for high temperature thermoelectrics. Thus, it is necessary to study the thermal properties of these materials in detail, especially thermal stability, to evaluate their potential. In this work, we report the synthesis and thermal stability study of five compounds, a-SrZrS3, b-SrZrS3, BaZrS3, Ba2ZrS4, and Ba3Zr2S7. These materials cover several structural types including distorted perovskite, needle-like, and Ruddlesden–Popper phases. Differential scanning calorimeter and thermogravimetric analysis measurements were performed up to 1200 °C in air. Structural and chemical characterizations such as X-ray diffraction, Raman spectroscopy, and energy dispersive analytical X-ray spectroscopy were performed on all the samples before and after the heat treatment to understand the oxidation process. Our studies show that perovskite chalcogenides possess excellent thermal stability in air at least up to 550 °C.
关键词： differential scanning calorimeter,thermoelectric materials,Transition metal perovskite chalcogenides,thermal stability,thermogravimetric analysis,Raman spectroscopy,Ruddlesden–Popper phases,X-ray diffraction,energy dispersive analytical X-ray spectroscopy
更新于2025-09-23 15:21:01
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Band Edge Tuning of Two-Dimensional Ruddlesdena??Popper Perovskites by A Cation Size Revealed through Nanoplates
摘要： Current understanding of the effects of various A site cations on the photophysical properties of halide perovskites (APbI3) is limited by the compositional tunability. Here we report the synthesis and characterization of colloidal nanoplates of a series of 2D Ruddlesden-Popper (RP) perovskites (HA)2(A)Pb2I7 (HA = n-hexylammonium) with seven small and large A site cations to reveal the size effects of such A cations. Absorbance and photoluminescence (PL) measurements show a clear parabolic trend of the optical band gap vs. the A cation size, with methylammonium and formamidinium near the bottom. This band gap shifting is attributed to the changing chemical pressure inside of the A site cavity templating the Pb-I framework. PL quantum yield and time resolved PL measurements show the effect of A cation size on the PL efficiencies and carrier lifetimes. This fundamental investigation can inform the choices of A site cations that can be incorporated into halide perovskite materials for optoelectronic applications.
关键词： chemical pressure,photoluminescence,A site cations,2D Ruddlesden-Popper perovskites,optical band gap
更新于2025-09-19 17:13:59
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Two-dimensional Ruddlesdena??Popper layered perovskite for light-emitting diodes
摘要： Solution-processed metal halide perovskite light-emitting diodes (PeLEDs) have attracted extensive attention due to the great potential application in energy-efficient lighting and displays. Two-dimensional Ruddlesden–Popper (2DRP) layered perovskites exhibit high photoluminescence quantum efficiency, improved film morphology, and enhanced operational stability over their three-dimensional counterparts, making them attractive for high-performance PeLEDs. In addition, 2DRP perovskite materials with a tunable exciton binding energy are suitable for preparing PeLEDs with color-tunability. In this perspective, we first introduce the merits of the 2DRP layered perovskites in terms of their structural characteristics. The progress in 2DRP PeLEDs is then reviewed. The challenges and new opportunities of the PeLEDs are finally discussed. We hope to open up new perspectives for rational designs of the 2DRP perovskite materials for PeLEDs with unprecedented efficiency and stability.
关键词： operational stability,film morphology,photoluminescence quantum efficiency,Two-dimensional Ruddlesden–Popper layered perovskite,color-tunability,light-emitting diodes
更新于2025-09-19 17:13:59