Ruddlesden-Popper Research Articles

Phase Tailoring of Ruddlesden-Popper Perovskite at Fixed Large Spacer Cation Ratio.

Ruddlesden-Popper (RP) metal halide perovskites are considered as promising optoelectronic materials due to their good environmental stability and desirable optoelectronic properties. However, the phase composition and ordering in the deposited film, with a fixed ratio of large organic spacer cation in the precursor solution, are hard to be further tailored for specific optoelectronic applications. Herein, it is shown that even with a fixed spacer cation ratio, the phase composition and ordering can still be largely regulated by utilizing different crystallization kinetics of various cations with the inorganic octahedral lead halide. By using two different short cations to compete with the large spacer cation, the phase composition can be continuously tailored from thin multiple quantum wells (MQWs) dominated to 3D perovskite dominated. The phase ordering can be reversed from small n phases' prior to large n phases' prior near the substrate. Finally, with the same amount of large spacer cation protection, the perovskite can be tailored for both high-performance electroluminescence and photovoltaics with favorable energetic landscape for the corresponding desired first-order excitonic recombination and second-order free electron-hole recombination, respectively. This exploration substantially contributes to the understanding of precise phase engineering in RP perovskite and may provide a new insight into the design of multiple functional devices.

Exciton-Phonon Interaction-Induced Large In-Plane Optical Anisotropy in Two-Dimensional All-Inorganic Perovskite Crystals.

Two-dimensional (2D) perovskites are an emerging class of layered materials with unique optoelectronic properties. To date, most 2D perovskites with Ruddlesden-Popper (RP) phase reported are organic- inorganic hybrid perovskites with long organic spacers. Here, we report a high-quality all-inorganic 2D perovskite, Cs2PbI2Cl2, synthesized by an aqueous method. The as-synthesized perovskite crystals exhibit large in-plane emission and reflection optical anisotropy. The maximum in-plane linear dichroic ratio is up to 9.6 for exciton emission and 2.0 for reflection at 77 K. The large in-plane optical anisotropy may be ascribed to the strong electron-phonon interaction-induced lattice distortion. The large optical anisotropy enables us to construct a polarization-sensitive photodetector based on this perovskite, for which the linear dichroic ratio of photoresponse is about 1.2. Our study provides an alternative avenue to achieve in-plane optical anisotropy in an isotropy structure and thus would be of great importance for polarization-associated applications.

Lewis Base Passivation of Quasi-2D Ruddlesden–Popper Perovskite for Order of Magnitude Photoluminescence Enhancement and Improved Stability

Quasi-two-dimensional (2D) Ruddlesden–Popper (RP) perovskites are currently considered as the material of choice for the next-generation light-emitting diodes (LEDs) due to their superior optoelect...

Theoretical study on the tunable electronic band structure of Cs2PbI2Cl2/CsPbBr3 halide perovskite heterostructure driven by ferroelectric polarization modulation

Ferroelectric polarizationhas been considered to be an key factor to tune the structural and photoelectric properties of perovskites and their heterostructures. While there has been growing researches made in the novel phenomena originating from interface formed between oxide perovskites, the effects of ferroelectric polarization on the electronic properties of halide perovskites and their heterostructures are rarely studied. Herein, by using first-principles calculations, all-inorganic halide perovskite heterostructure composed of 3D perovskite tetragonal CsPbBr3 and 2D Ruddlesden-Popper (RP) perovskite Cs2PbI2Cl2 is constructed for disclosing the relationship between the intrinsic polarization of tetragonal CsPbBr3 and electronic band structure of heterostructure. Cs atoms and Pb atoms of tetragonal CsPbBr3 in heterostructure are artificially moved away from the equivalent centers to simulate increased polarization. Our results show that with the spontaneous polarization of tetragonal CsPbBr3 increasing, the bandgap of heterostructure decreases, and the band alignment switches from staggered type-II to broken-gap type-III. Moreover, large cation–anion displacements along z-direction in tetragonal CsPbBr3 can be observed when tensile strains (≥5%) are applied, indicating a increased ferroelectric polarization, which also facilitates the decreasing of bandgap in heterostructure and the type-II-type-III transition of band alignment. Our study suggests that control over the polarization of ferroelectric materials is of great importance to tune the photoelectric properties of perovskite-based devices.

Inhibiting in situ phase transition in Ruddlesden-Popper perovskite via tailoring bond hybridization and its application in oxygen permeation

Inhibiting in situ phase transition in Ruddlesden-Popper perovskite via tailoring bond hybridization and its application in oxygen permeation

Revealing a high-density three-dimensional Ruddlesden–Popper-type fault network in an SmNiO3 thin film

An epitaxial SmNiO3 thin-film grown on an LaAlO3 (001) substrate using pulsed laser deposition is investigated with spherical-aberration corrected scanning transmission electron microscopy techniques, including high-angle annular dark field, X-ray energy dispersive, and electron energy-loss spectroscopy. High-density Ruddlesden–Popper (RP)-type faults, which generate two types of image contrast due to overlaps along the electron beam direction, are identified with the translational vector of 1/2a⟨111⟩c, corresponding to 1/2a⟨101⟩c displacement of Sm atoms when observed along the [010]c zone axis. These defects originate from Sm-rich non-stoichiometry within the SmNiO3, and their directions depend on the local stress states. Lattice distortion induced by the RP faults reduces the metal-to-insulator transition temperature to around 340 K. The effects of high-density RP faults on the lattice strain, domain size, and strong electronic-lattice correlations indicate that RP faults can provide extra freedom to tailor the physical properties of SmNiO3 thin films for potential electronic device applications. High-density Ruddlesden–Popper-type faults are revealed in an epitaxial SmNiO3 thin film grown on LaAlO3 (001) by pulsed laser deposition, originating from Sm-rich non-stoichiometry, and their directions depend on the local stress states. Lattice distortion induced by the RP faults reduces the metal-to-insulator transition temperature to around 340 K. RP faults provide extra freedom to tailor intriguing properties of SmNiO3 for potential electronic device applications.

Interfacial resistive switching of Ruddlesden–Popper phase strontium titanate thin film by charge-modulated Schottky barrier

Ruddlesden–Popper (RP) phase Sr2TiO4 thin film is deposited successfully on FTO/glass substrate by spin coating. X-ray diffraction (XRD) pattern shows high-intensity (00 l) (l = 2, 4, and 6) peaks. The device shows bipolar resistive switching (RS) effect. Analysis on current–voltage (I-V) characteristic shows that conduction mechanism is dominated by Schottky emission in both low resistive state (LRS) and high resistive state (HRS). A variation (~0.12 eV) in Schottky barrier height (SBH) is observed between HRS and LRS. Thus, RS at electrode-Sr2TiO4 interface is the main mechanism. In general, variation of SBH is induced by accumulation of interfacial charges. Polarization-voltage (P-V) measurement shows hysteresis loop, which indicates the accumulation of interfacial charges. Formation and migration of charged oxygen vacancies and ions is proposed to be a possible mechanism of interfacial charges accumulation. This study paves the avenue for exploring RS application based on RP phase Sr2TiO4 perovskite oxide.

A‐Site Cation Engineering in 2D Ruddlesden–Popper (BA)2(MA1‐xAx)2Pb3I10 Perovskite Films

AbstractThe partial incorporation of large organic cations into the octahedral sites of 3D perovskites has been widely investigated but few works have reported their addition in 2D Ruddlesden–Popper (RP) perovskites. Here, the gradual substitution of the methylammonium (MA) cation in thin films of 2D RP perovskites (BA)2(MA)2Pb3I10 (BA = n‐butylammonium) by guanidinium (Gua), dimethylammonium (DA), ethylammonium (EA), rubidium (Rb), propylammonium (PA), cesium (Cs) or formamidinium (FA) to synthesize mixed A‐cation (BA)2(MA1‐xAx)2Pb3I10 perovskites has been studied. The limit in the percentage of the A‐site cation at which it is homogeneously incorporated in all n phases without destabilizing the overall structure is determined. It is found that the structural changes in the 2D RP perovskites may lead to modifications of the optoelectronic properties as larger bandgap (EA), blue‐shift of the PL peak position (above the threshold), strong quenching of the PL (Cs) or reduced concentration of trap states (Gua and EA). Solar devices fabricated with the different mixed A‐cation 2D RP display an enhanced performance for those perovskites containing low percentages of Gua or EA cations. This characterization is very valuable to correlate the size and shape of the A‐cation with the changes of the properties of the material.

Signatures of Coherent Phonon Transport in Ultralow Thermal Conductivity Two-Dimensional Ruddlesden–Popper Phase Perovskites

An emerging class of methylammonium lead iodide (MAPbI3)-based Ruddlesden-Popper (RP) phase perovskites, BA2MAn-1PbnI3n+1 (n = 1-7), exhibit enhanced stability to environmental conditions relative to MAPbI3, yet still degrade at elevated temperatures. We experimentally determine the thermal conductivities of these layered RP phases for n = 1-6, where n defines the number of repeated perovskite octahedra per layer. We measure thermal conductivities of 0.37 ± 0.13/0.12, 0.17 ± 0.08/0.07, 0.21 ± 0.05/0.04, and 0.19 ± 0.04/0.03 W/m·K in thin films of n = 1-4 and 0.08 ± 0.06/0.04, 0.06 ± 0.04/0.03, 0.06 ± 0.03/0.03, and 0.08 ± 0.07/0.04 W/m·K in single crystals of n = 3-6. With the exception of n = 1, these thermal conductivities are lower than the range of 0.34-0.50 W/m·K reported for single-crystal MAPbI3. Reduced-order lattice dynamics modeling suggests that the initially decreasing trend of thermal conductivity in similarly oriented perovskites with increasing n may result from the transport properties of coherent phonons, emergent from the superstructure, that do not scatter at the interfaces of organic butylammonium chains and perovskite octahedra. Reduced group velocity of coherent phonons in n = 3-6, a consequence of band flattening in the phonon dispersion, is primarily responsible for their ultralow thermal conductivities. Similar effects on thermal conductivity have been experimentally demonstrated in deposited superlattices, but never in naturally defined materials such as RP phases. GIWAXS measurements reveal that higher n RP phase thin films are less orientationally controlled and therefore possess apparently elevated thermal conductivities relative to single crystals of the same n.

Tailoring c‐Axis Orientation in Epitaxial Ruddlesden–Popper Pr0.5Ca1.5MnO4 Films

AbstractInterest in layered Ruddlesden–Popper (RP) strongly correlated manganites of Pr0.5Ca1.5MnO4 as well as in their thin film polymorphs is motivated by the high temperature of charge orbital ordering above room temperature. The c‐axis orientation in epitaxial films is tailored by different SrTiO3 (STO) substrate orientations and CaMnO3 (CMO) buffer layers. Films on STO(110) show in‐plane alignment of the c‐axis parallel to the [100] direction. On STO(100), two possible directions of the in‐plane c‐axis lead to a mosaic like, quasi 2D nanostructure, consisting of RP, rock‐salt, and perovskite blocks. With the CMO buffer layer, Pr0.5Ca1.5MnO4 epitaxial films with c‐axis out‐of‐plane are realized. Different physical vapor deposition techniques as ion beam sputtering, pulsed laser deposition and metalorganic aerosol deposition are applied in order to distinguish effects of growth conditions from intrinsic epitaxial properties. Despite their very different growth conditions, surface morphology, crystal structure, and orientation of the thin films reveal a high level of similarity as verified by X‐ray diffraction, scanning, and high resolution transmission electron microscopy. For different epitaxial relations stress in the films is relaxed by means of modified interface chemistry. The charge ordering in the films occurs at a temperature close to that expected in bulk material.

Smoothing the energy transfer pathway in quasi-2D perovskite films using methanesulfonate leads to highly efficient light-emitting devices

Quasi-two-dimensional (quasi-2D) Ruddlesden–Popper (RP) perovskites such as BA2Csn–1PbnBr3n+1 (BA = butylammonium, n > 1) are promising emitters, but their electroluminescence performance is limited by a severe non-radiative recombination during the energy transfer process. Here, we make use of methanesulfonate (MeS) that can interact with the spacer BA cations via strong hydrogen bonding interaction to reconstruct the quasi-2D perovskite structure, which increases the energy acceptor-to-donor ratio and enhances the energy transfer in perovskite films, thus improving the light emission efficiency. MeS additives also lower the defect density in RP perovskites, which is due to the elimination of uncoordinated Pb2+ by the electron-rich Lewis base MeS and the weakened adsorbate blocking effect. As a result, green light-emitting diodes fabricated using these quasi-2D RP perovskite films reach current efficiency of 63 cd A−1 and 20.5% external quantum efficiency, which are the best reported performance for devices based on quasi-2D perovskites so far.

Mechanochemical Synthesis, Optical and Magnetic Properties of Pb-Free Ruddlesden–Popper-Type Layered Rb2CuCl2Br2 Perovskite

2D layered Ruddlesden–Popper (RP) perovskites gained significant attention owing to their unique optoelectronic properties and ultralow thermal conductivity; however, in comparison to the hybrid Pb...

Spectroscopic and transport properties of Ba‐ and Ti‐doped BaLaInO4

AbstractIn this work, the local structure of the acceptor Ba1+хLa1–хInO4–0.5х and donor BaLaIn1–хTiхO4+0.5х doped solid solutions based on BaLaInO4 was investigated. The appearance of new types of the defects (oxygen vacancy and oxygen interstitial) in the crystal lattice was confirmed by the spectroscopic investigations. It was shown that for both solid solutions the same tendency of the increase in the symmetry of the structure and the expansion of interlayer space with increasing dopant concentration is observed. The changes in the transport properties (ionic conductivity) have the same tendency for both solid solutions. The increase in the oxygen‐ionic and protonic conductivity in the area of “low” dopant concentrations (x < 0.05) is due to the increase in the mobility of ions caused by the influence of geometric factor. The decrease in the ionic conductivity values in the area of “high” dopant concentrations (x > 0.05) is caused by the appearance of interaction between defects (concentration factor). The most conductive ionic (oxygen‐ionic and protonic) material with Ruddlesden–Popper (RP) structure based on BaLaInO4 is Ba1.1La0.9InO3.95 composition.

Effective Phase Control for High-Performance Red-Light-Emitting Quasi-2D Perovskite Solar Cells via MACl Additive

Quasi-2D Ruddlesden–Popper (RP) perovskite films have been widely used in fabricating high-performance perovskite light-emitting diodes (PeLEDs) and solar cells because of their environmental stabi...

Crystallinity-dependent device characteristics of polycrystalline 2D n = 4 Ruddlesden–Popper perovskite photodetectors

Ruddlesden–Popper (RP) perovskites have attracted a lot of attention as the active layer for optoelectronic devices due to their excellent photophysical properties and environmental stability. Especially, local structural properties of RP perovskites have shown to play important roles in determining the performance of optoelectronic devices. Here, we report the photodetector performance variation depending on the crystallinity of n = 4 two-dimensional (2D) RP perovskite polycrystalline films. Through controlling the solvent evaporation rate, 2D RP perovskite films could be tuned between highly- and randomly-orientated phases. We investigated how different factors related to the film crystallinity are reflected in the variation of photodetector performances by considering grain boundary and low energy edge state effects in n = 4 RP perovskites. Better understanding the interplay between these factors that govern the photophysical properties of the devices would be beneficial for designing high-performance RP perovskite-based optoelectronic devices.

Two-Dimensional Dion–Jacobson Structure Perovskites for Efficient Sky-Blue Light-Emitting Diodes

Two-dimensional Ruddlesden–Popper (RP) and Dion–Jacobson (DJ) phase perovskites are promising alternatives to fabricate blue perovskite light-emitting diodes (PeLEDs) due to their strong quantum/di...

Layer Shift Factor in Layered Hybrid Perovskites: Univocal Quantitative Descriptor of Composition–Structure–Property Relationships

Asceding interest of the scientific community in layered hybrid halide perovskites (LHHPs) as materials for innovative photovoltaic and optoelectronic applications led to unprecedented expansion of this family of compounds, reaching now several hundred refined structures. Despite the unique structural diversity of LHHPs, traditional approaches of describing their structures, such as dividing into Dion-Jacobson (DJ) or Ruddlesden-Popper (RP) phases for mostt structures are ambiguous and unquantifiable. Here, we introduced a quantitative layer shift factor (LSF) for a univocal classification and quantitative comparison of the structures. We also developed an algorithm for automatic calculation of the LSF for such structures. We demonstrate the application of the proposed approach for an analysis of correlations between LSF and band gap to reveal "structure-property" relationships. Our study gives a simple and useful approach to classify of either the layered perovskite-like structures or other layered compounds composed of layers of vertex-connected octahedra as a structural unit.

Oxidation and Storage Mechanisms for Nitrogen Oxides on Variously Terminated (001) Surfaces of SrFeO3-δ and Sr3Fe2O7-δ Perovskites.

The Ruddlesden-Popper (RP)-type layered perovskite is a candidate material for a new nitrogen oxide (NOx) storage catalyst. Here, we investigate the adsorption and oxidation of NOx on the (001) surfaces of RP-type oxide Sr3Fe2O7-δ for all of the terminations by comparing to those of simple perovskite SrFeO3-δ by the density functional theory (DFT) calculations. The possible (001) cleavages of Sr3Fe2O7 generate two FeO2- and three SrO-terminated surfaces, and the calculated surface energies indicated that the SrO-terminated surface generated by the cleavage at the rock salt layer is the most stable one. The oxygen of the FeO2-terminated surfaces could be removed with significantly low energy because the process involves the favorable reduction of the Fe4+ site. Consequently, the surface oxygen at the FeO2 site could easily oxidize adsorbed NO to NO2 by the Mars-van Krevelen mechanism. The resulting oxygen vacancy in the surface would be filled easily with lattice oxygen in bulk. The oxidation of NO with adsorbed molecular O2 was unfavorable by both the Langmuir-Hinshelwood and Eley-Rideal mechanisms because this process does not involve the reduction of the Fe4+ site. The oxygen of the SrO-terminated surfaces was tightly bound and acted as the adsorption site of NO and NO2. An electron transfer strengthened the NOx binding to the surface by forming nitrite (NO2-) or nitrate (NO3-) species. The DFT calculations revealed that the RP-type structure promoted NOx oxidation and storage properties by forming active oxygen due to the Jahn-Teller distortion and by exposing SrO-terminated surfaces due to the cleavage at the rock salt layer.

Effects of Cl and F Substitution in Phenylethylammonium Spacer Cations on Stability, Structure, and Optical Properties of 2D–3D Ruddlesden–Popper Perovskite Layers

Recent experiments on chemical tuning of spacer cations (phenylethylammonium: PEA) with electronegative entities such as Cl or F in 2D–3D Ruddlesden–Popper (RP) perovskite layers show simultaneous ...

High-Quality Ruddlesden-Popper Perovskite Film Formation for High-Performance Perovskite Solar Cells.

In the last decade, perovskite solar cells (PSCs) have undergone unprecedented rapid development and become a promising candidate for a new-generation solar cell. Among various PSCs, typical 3D halide perovskite-based PSCs deliver the highest efficiency but they suffer from severe instability, which restricts their practical applications. By contrast, the low-dimensional Ruddlesden-Popper (RP) perovskite-based PSCs have recently raised increasing attention due to their superior stability. Yet, the efficiency of RP perovskite-based PSCs is still far from that of the 3D counterparts owing to the difficulty in fabricating high-quality RP perovskite films. In pursuit of high-efficiency RP perovskite-based PSCs, it is critical to manipulate the film formation process to prepare high-quality RP perovskite films. This review aims to provide comprehensive understanding of the high-quality RP-type perovskite film formation by investigating the influential factors. On this basis, several strategies to improve the RP perovskite film quality are proposed via summarizing the recent progress and efforts on the preparation of high-quality RP perovskite film. This review will provide useful guidelines for a better understanding of the crystallization and phase kinetics during RP perovskite film formation process and the design and development of high-performance RP perovskite-based PSCs, promoting the commercialization of PSC technology.