Ruddlesden-Popper Perovskites Research Articles

Gradient 2D–3D Ruddlesden-Popper perovskite film for high-performance self-powered photodetectors

Quasi-2D Ruddlesden–Popper perovskites have been widely used in the photoelectric detection field owing to their tunable optical bandgap and superior stability. However, because phases formed in the quasi-2D perovskite films have unfixed n values, the transport channels of charge carriers are greatly disordered. Herein, based on the hot-casting method, the effects of substrate temperature on the surface morphology and internal phases distribution of 2D perovskite films was investigated, leading to the preparation of uniform and compact 2D–3D gradient perovskite thin films. Perovskites have an orderly gradient phase distribution along the longitudinal direction of the thin film, which is beneficial to the separation and transport of carriers, thus improving the photosensitivity of photodiode over the whole visible spectrum range. The ideal photodetector fabricated at 120 ℃ has an extremely low dark current density (2.3 × 10−11A/cm2), large specific detectivity (1.22 × 1014 Jones) at 455 nm, ultra-fast response time (5.5/4.7 µs) and ultra-high on/off ratio of 108, indicating its great potential for high-efficiency photodetection without the voltage bias (0 V). Moreover, compared with 3D perovskite devices, hot-casted 2D perovskite devices exhibit greatly improved stability, with JD remaining at about 10−11A/cm2 for 400 h, which is very significant for realizing outstanding performance and stable photodiodes.

Pinhole-free 2D Ruddlesden–Popper perovskite layer with close packed large crystalline grains, suitable for optoelectronic applications

Here, we achieved pinhole-free 2D Ruddlesden–Popper Perovskite (RPP) BA2PbI4 layers with close packed crystalline grains with dimension of about 30 × 30 µm2, which have been demonstrated to be favorable for optoelectronic applications, such as fast response RPP-based metal/semiconductor/metal photodetectors. We explored affecting parameters in hot casting of BA2PbI4 layers, and proved that oxygen plasma treatment prior to hot casting plays a significant role to achieve high quality close packed polycrystalline RPP layers at lower hot cast temperatures. Moreover, we demonstrate that crystal growth of 2D BA2PbI4 can be dominantly controlled by the rate of solvent evaporation through substrate temperature or rotational speed, while molarity of the prepared RPP/DMF precursor is the dominant factor that determines the RPP layer thickness, and can affect the spectral response of the realized photodetector. Benefiting from the high light absorption and inherent chemical stability of 2D RPP layers, we achieved high responsivity and stability, and fast response photodetection from perovskite active layer. We achieved a fast photoresponse with rise and fall times of 189 µs and 300 µs, and the maximum responsivity of 119 mA/W and detectivity of 2.15 × 108 Jones in response to illumination wavelength of 450 nm. The presented polycrystalline RPP-based photodetector benefits from a simple and low-cost fabrication process, suitable for large area production on glass substrate, a good stability and responsivity, and a promising fast photoresponse, even around that of exfoliated single crystal RPP-based counterparts. However, it is well known that exfoliation methods suffer from poor repeatability and scalability, which make them incompatible with mass production and large area applications.

Proton-Mediated Structural and Optical Recovery of a UV-Degraded Colloidal Ruddlesden–Popper Perovskite Nanoplate for Prolonged Application

Two-dimensional Ruddlesden–Popper (RP) lead halide perovskite nanoplates (NPls) have recently attracted attention due to their superior properties in optoelectronics. However, structural degradation of these materials under continuous photoexcitation restricts their acceptability. Herein, we report an instantaneous structural as well as optical recovery of colloidal (OAm)2(CH3NH3PbI3)2PbI4 RP NPls from its UV-degraded stage through a simple “protonation” approach by proton-donating species like 1-dodecanethiol, 4-aminothiophenol, and hydroiodic acid.

Inhibiting in Situ Phase Transition in Ruddlesdenpopper Perovskite Via Tailoring Bond Hybridization for Oxygen Ion Conduction

Owing to the excellent physical and chemical properties, mixed ionic-electronic conducting oxides, especially Ruddlesden-Popper (RP)perovskite oxides, are interesting materials for environment and energy research. Phase transition is a common phenomenon for these materials, which generally exerts a great influence on the properties and functionalities. Element-doping has been recognized as a facile and efficient strategy to improve the oxygen ionic or electronic conductivity or to stabilize the crystal phase structure. However, in-depth understanding of the mechanism of phase transition is still limited so far. Herein, we try to reveal the mechanism of molybdenum substitution in B-site of RP perovskite (Pr2NiO4) to induce the ex-situ collapse and to inhibit the in-situ phase transition. This work not only provides a thorough explanation of the phase transition process based on element doping but also presents a novel high-performance oxygen permeation membrane.

Sr3Fe1.5Zn0.5O7-δ as Cathode for Protonic-Conducting Solid Oxide Fuel Cells with Enhanced Oxygen Reduction Reaction Activity

Perovskite oxides have attracted intensive attention for their good electrochemical performance and stability as electrodes for protonic ceramic fuel cells (PCFCs). However, operating under high temperatures and various atmospheres results in a large polarization resistance and sluggish oxygen reduction reaction (ORR) in cathodes. Here, Zn was successfully doped into Sr3Fe2O7-δ (SFO) Ruddlesden-Popper (RP) perovskite cathode and the Sr3Fe1.5Zn0.5O7-δ (SFZ05) shows a superior ORR activity. The polarization resistance of SFZ05 is 0.072 Ω·cm-2, which is 47% lower than that of the undoped SFO, and the maximum peak power density of the single-cell of NiO-BaZr0.1Ce0.7Y0.2O3-δ(BZCY)|BZCY|SFZ05 reaches 523.56 mW·cm-2 at 750℃, increased by 22% than SFO. The improvement is attributed to the formation of oxygen vacancies and the increase of proton conductivity. These results display that SFZ05 is a promising candidate for a highly active and stable cathode for PCFCs.

Efficient Narrowband Photoconductivity of the Excitonic Resonance in Two-Dimensional Ruddlesden-Popper Perovskites Due to Exciton Polarons.

Filter-less, wavelength-selective photodetectors made of perovskite usually rely on the charge collection narrowing mechanism, which intrinsically limits the response times. Using the narrow excitonic peak of, e.g., two-dimensional (2D) Ruddlesden-Popper perovskites as direct absorbers to realize color-selective photodetectivity promises faster responses. However, one major challenge in realizing such devices remains the separation and charge carrier extraction of the tightly bound excitons. Here, we report on filter-less color-selective photoconductivity in 2D perovskite butylammonium lead iodide thin film devices, exhibiting a distinct resonance in the photocurrent spectrum with a full width at half-maximum of 16.5 nm that correlates to the excitonic absorption. Our devices exhibit unexpectedly efficient charge carrier separation with an external quantum efficiency of ≤8.9% at the excitonic resonance, which we trace back to the involvement of exciton polarons. Our photodetector achieves response times of 150 μs and a maximum specific detectivity of 2.5 × 1010 Jones at the excitonic peak.

Bulk Incorporation of Molecular Dopants into Ruddlesden–Popper Organic Metal–Halide Perovskites for Charge Transfer Doping

AbstractOrganic metal‐halide perovskites (OHPs) have recently attracted much attention as next‐generation semiconducting materials due to their outstanding opto‐electrical properties. However, OHPs currently suffer from the lack of efficient doping methods, while the traditional method of atomistic doping having clear limitations in the achievable doping range. While doping with molecular dopants, has been suggested as a solution to this problem, the action of these dopants is typically restricted to perovskite surfaces, therefore significantly reducing their doping potential. In this study, successful bulk inclusion of “magic blue”, a molecular dopant, into 2D Ruddlesden–Popper perovskites is reported. This doping strategy of immersing the perovskite film in dopant solution increases the electrical current up to ≈60 times while maintaining clean film surface. A full mechanistic picture of such immersion doping is provided, in which the solvent molecule facilitates bulk diffusion of dopant molecule inside the organic spacer layer. Physical criteria for judicious choice of solvents in immersion doping are developed based on readily available solvent properties. The immersion doping method developed in this study that enables bulk molecular doping in OHPs will provide a strategic doping methodology for controlling electrical properties of OHPs for electronic and optoelectronic devices.

Fluorinated 2-Phenylethylammonium Spacer Cations for Improved Stability of Ruddlesden–Popper Pb/Sn Halide Perovskites: Insight from First-Principles Calculations

Improving the stability of hybrid halide perovskite solar cells is essential for their commercialization in emerging cutting-edge technology. Here, we report the results of state-of-the-art first-principles calculations to achieve and understand enhancement in the stability of Ruddlesden–Popper (RP) lead/tin halide perovskites with fluorinated 2-phenylethylammonium (PEA) spacer cations. It is found that the substitution of up to five F atoms in the phenyl ring makes C slightly positively charged due to ∼0.5e charge transfer to electronegative F. This leads to the formation of electric dipoles in the spacer cation region and polarization of the charge density. This improves the formation energy and enhances the stability of the layers. The charge transfer makes some of the C 2p orbitals partly empty so that they hybridize with F 2p orbitals near the conduction band minimum. This is interesting for the charge transport perpendicular to the layers. Our study further shows that changing the metal cations Pb with Sn does not affect the orientation of the cation molecules in the pure as well as chemically tuned RP layers whereas changing the halide ions I with Br has an impact on the orientation of the organic molecules. The calculated structures of the layers agree well with the available experimental results and suggest structures of some unexplored layers that would be interesting to fabricate. The calculated electronic structure and optical properties show that the absorption coefficient is high (∼105 cm–1) for the layers having heavily fluorinated spacer cations. Furthermore, we find higher stability and a desirable lower direct band gap for Sn-based green perovskite layers compared to the Pb counterparts. Our results provide computational insight into the surface engineering of RP perovskites for further developments in this fast-growing area.

Tetracycline hydrochloride degradation by activation of peroxymonosulfate with lanthanum copper Ruddlesden-Popper perovskite oxide: Performance and mechanism

ABO3-type perovskite oxides have been regarded as a kind of potential catalyst for peroxymonosulfate (PMS) activation. But some limitations such as specific pH conditions and coexisting ion interference restrict its practical application. Herein, a lanthanum copper Ruddlesden-Popper perovskite oxide (La2CuO4) was successfully synthesized through the sol-gel process and applied in the activation of PMS. And for the first time the La2CuO4/PMS system was used for tetracycline hydrochloride (TC-HCl) degradation. Results showed that La2CuO4 was a potential PMS activation catalyst in the removal of antibiotics. At optimized condition (0.2 g/L catalysts, 1 mM PMS, pH0 6.9), 96.05% of TC-HCl was removed in 30 min. In experiments of debugging control conditions, over a wide pH range of 3–11, more than 90% of TC-HCl can be removed. In the natural water treatment process, TC-HCl removal rates of about 84.2% and 70.3% were obtained in tap water and River water, respectively. According to the reusability and stability tests and the results of FTIR and XPS analysis, La2CuO4 had high structural and chemical stability. Electron paramagnetic resonance (EPR) suggested that the active species including ·OH, SO4−· and 1O2 were detected in degradation reaction. Finally, reasonable reaction mechanisms and possible degradation pathways of TC-HCl were proposed. These results indicate that La2CuO4 can act as a potential catalyst for PMS activation to degrade TC-HCl in water.

Dynamic Distortions of Quasi-2D Ruddlesden–Popper Perovskites at Elevated Temperatures: Influence on Thermal and Electronic Properties

Ruddlesden–Popper hybrid halide perovskites are quasi-two-dimensional materials with a layered structure and structural dynamics that are determined by the interplay between the organic and inorganic layers. While their optical properties are governed by confinement effects, the atomistic origin of thermal and electronic properties of these materials is yet to be fully established. Here we combine computational and experimental techniques to study A2PbI4 (A = butylammonium (BA), phenethylammonium (PEA)) Ruddlesden–Popper perovskites and compare them with the quintessential perovskite CH3NH3PbI3. We use first-principles density functional theory, molecular dynamics simulations based on machine-learned interatomic potentials, thermal measurements, temperature-dependent Raman spectroscopy, and ultraviolet photoelectron spectroscopy to probe the thermal and electronic properties of these materials at elevated temperatures. Our molecular dynamics simulations demonstrate that dynamic fluctuations in the organic sublattice determine the bulk-average distortions of these materials at room temperature, explaining significant differences in their electronic density of states close to the Fermi level. Furthermore, by analyzing the organic layer dynamics in BA2PbI4 we provide a mechanistic explanation for the phase transition of this material at 274 K and observations from Raman measurements. Our results highlight the role of the organic interlayer for the electronic and thermal transport properties of Ruddlesden–Popper perovskites, paving the way for the design of new hybrid materials for tailored applications.

Phase‐Purified Ruddlesden–Popper Perovskites Vertically Oriented in Block Copolymer Nanostructures for Environmentally Stable Light Conversion and Charge Trapping

Abstract2D Ruddlesden–Popper perovskites (RPPs) with 2D layer‐tunable optoelectronic properties suffer from randomly oriented multiple phases. Herein, an efficient method for developing RPP films with controlled phase purity and crystal orientation via a one‐step synthesis of RPPs in a self‐assembled block copolymer (BCP) film is demonstrated. RPP crystals with a target phase <n = 2 or 3> are preferentially embedded in the poly(ethylene oxide) domains of a polystyrene‐block‐poly(ethylene oxide) nanostructured film. Interestingly, rapid self‐assembly with the BCP results in phase‐purified n = 2 and 3 targeted RPPs with a target phase percentage two and four times higher, respectively, than that of pristine RPP. Furthermore, RPP crystals synthesized within BCP are preferentially oriented with their b‐axis parallel to the surface normal. The photoluminescence of the composite film is significantly enhanced, allowing environmentally stable ultraviolet‐to‐blue color conversion. Moreover, semiconducting RPP crystals nanopatterned in the BCP are successfully used as charge‐trapping floating nanogates, resulting in a non‐volatile field‐effect transistor memory.

Ruddlesden–Popper Perovskite Alloys: Continuous and Discontinuous Tuning of the Electronic Structure

Alloying mixed ratios of elements into the halide perovskite (HP) structure has proven to be an effective method of tuning these materials’ structural and electronic properties for photovoltaic and other optoelectronic applications. However, the standard spectroscopies used to characterize HP alloys such as absorption and photoluminescence are limited in their ability to detect disorder and phase segregation within the structure. Here, we characterize these properties in 2D HP alloys to a greater degree by using electroabsorption spectroscopy to study thin films with mixed-metal (Pb–Sn) and mixed-halide (Br–Cl and Br–I) compositions. The large spectral separation of band-edge states in 2D HPs allow us to detect a coexistence of elemental-rich domains within the Pb–Sn and Br–I alloys. Meanwhile, we find that the Br–Cl alloys exhibit sharper spectral features and a more uniform electroabsorption response indicative of an ordered structure, albeit still not as ordered as their pure Br and Cl counterparts. The band gap energies of the Br–Cl series (PEA2PbBrxCl4 – x) can be continuously tuned between 3.425 and 4.13 eV via the Br:Cl ratio, while the exciton binding energies can be tuned from 349 to 487 meV.

High‐Quality Lead Acetate–Based Ruddlesden–Popper Perovskite Films for Efficient Solar Cells

The 2D Ruddlesden–Popper perovskites (RPPs), consisting of alternating organic spacer layers and inorganic layers, are emerging photovoltaic materials because of their highly tunable optoelectronic properties and improved stability compared to their 3D counterparts. Nonhalide lead sources attract increasing attention in 3D perovskites, whereas the lead sources for RPPs are limited to lead halides. Herein, nonhalide lead source of lead acetate is investigated for high‐quality RPP films by a dimethyl sulfoxide (DMSO)‐assisted delayed annealing process. The incorporation of DMSO in the lead acetate–based precursor solution regulates the crystallization process, resulting in RPP films with distinctly enhanced crystallinity, reduced trap density, vertical crystal orientation, and graded phase distribution. Consequently, the optimized RPP solar cell with an inverted planar structure delivers a champion power conversion efficiency of 17.3%. Herein, future developments of nonhalide lead sources are spurred to fabricate RPP films with high device performance.

Investigation of catalytic reduction of NO by CO over A- and B- site substituted La(Sr)Fe(Co)O3 perovskites

In this study, La1−xSrxFeO3 and LaFe1−xCoxO3 perovskites with different La/Sr and Fe/Co ratios have been synthesized via auto combustion method using glycine as fuel. After complete characterization, the catalytic activity of the perovskites was evaluated in the nitrogen monoxide reduction by carbon monoxide, in a lab-scale plug flow reactor. The most active catalysts were La0.75Sr0.25FeO3 and LaFe0.25Co0.75O3. Substitution in different sites of perovskite structure influences differently the catalytic activity and selectivity. The A-site substitution of La by Sr resulted in decrease of activity due to the presence of strontium carbonate, formed by strong adsorption of the produced carbon dioxide on the catalyst surface while selectivity of the reaction is correlated with the oxygen reverse uptake. The B-site substitution of Fe by Co increases the activity due to the partial -reduction of the classic ABO3 phase to A2BO4 Ruddlesden-Popper perovskite phase La2CoO4.

Minimal Molecular Building Blocks for Screening in Quasi-Two-Dimensional Organic-Inorganic Lead Halide Perovskites.

Layered hybrid organic-inorganic lead halide perovskites have intriguing optoelectronic properties, but some of the most interesting perovskite systems, such as defective, disordered, or mixed perovskites, require multiple unit cells to describe and are not accessible within state-of-the-art ab initio theoretical approaches for computing excited states. The principal bottleneck is the calculation of the dielectric matrix, which scales formally as O(N4). We develop here a fully ab initio approximation for the dielectric matrix, known as IPSA-2C, in which we separate the polarizability of the organic/inorganic layers into minimal building blocks, thus circumventing the undesirable power-law scaling. The IPSA-2C method reproduces the quasi-particle band structures and absorption spectra for a series of Ruddlesden-Popper perovskites to high accuracy, by including critical nonlocal effects neglected in simpler models, and sheds light on the complicated interplay of screening between the organic and inorganic sublattices.

Controllable Synthesis of Centimeter-Sized 2D Ruddlesden–Popper Perovskite Single Crystals through Intermediate-Phase Engineering

Controllable Synthesis of Centimeter-Sized 2D Ruddlesden–Popper Perovskite Single Crystals through Intermediate-Phase Engineering

Controllable Transformation of 2D Perovskite for Multifunctional Sensing Properties

There is growing demand for convenient and cost-efficient ethanol sensing techniques in daily life and industry. However, the complexity, high cost, and large volume of the equipment hinder the widespread use of conventional ethanol sensing techniques. Here, we introduce a test paperlike visualized label-free ethanol sensing platform by taking advantage of the instability of 2D Ruddlesden–Popper perovskite in ethanol. The photoluminescence of PEA2Csn–1PbnBr3n+1 2D perovskite changes from deep blue to green distinctly when exposed to ethanol. A cheap demo ethanol test paper is fabricated by this 2D perovskite and paper using a simple method, demonstrating interesting rapid and convenient ethanol sensing performance. Crystal analysis, constituent analysis, spectral analysis, and molecular dynamic (MD) simulation reveal the crystal structure transformation from 2D to 3D induced by the migration of PEA+ cations in the original 2D perovskite when exposed to ethanol. In addition, a chemiresistive sensor based on the 2D perovskite and on the 2D–3D phase transformation is developed and demonstrates a high ethanol detection sensitivity with a limit down to 0.7 ppm. The photodetector fabricated by the 2D perovskite also demonstrates tunable sensitivity upon the controllable 2D–3D transformation. This remarkable colorimetric, chemiresistive, and photosensitive perovskite is expected to highlight its future application and be a supplement to the existing ethanol sensing and photodetector techniques.

Strained induced metallic to semiconductor transitions in 2D Ruddlesden Popper perovskites: A GGA + SOC approach

Based on RP perovskites, we put 2%, 4%, 6%, and 8% biaxial strains on 2D monolayers of phenyl-ammonium tin iodide (PH2SnI4) perovskites. Density functional theory (DFT) is used to study the structural distortion, octahedral tilting, band gap tuning, Bader charge analysis, and mechanical stability of the resulting configurations. Band gaps under the effects of compressive strain (Eg1), zero strain (Eg2), and tensile strain (Eg3) follow a decreasing order of Eg1(1.262 eV) < Eg2(1.329 eV) < Eg3(1.331 eV) for 6%-strain. The absence of trap states in energy band gaps and dominant cation and anion contributions at conduction and valence band edges supports the defect tolerance. All the structures analyzed are mechanically stable. The covalently bonded structures are ductile/brittle under tensile/compressive strain, with a prominent stretching mode. Strain improves the optical performance with dielectric constant increased (red-shifted) under compressive strain and reduced (blue-shifted) under compressive strain.

Stereopsis-Inspired 3D Visual Imaging System Based on 2D Ruddlesden-Popper Perovskite.

Stereopsis is of great important functions for humans to perceive and interact with the world. To realize the function of stereoscopic imaging, optoelectronic sensors shall possess good photoresponsive performance, multidirectional sensing, and 3D building capabilities. However, the current imaging sensors are mainly focused on 2D imaging, limiting their practical application scenarios. In this study, a stereopsis-inspired flexible 3D visual imaging system (VIS) based on 2D Ruddlesden-Popper perovskite is demonstrated. The 3D-VIS consists of 800 device units, each of which demonstrates excellent photoresponse performance, mechanical characteristics, and environmental stability. In addition to the capability of detecting 2D reflective images, the 3D-VIS realizes the function of detecting the depth of field and fusing object projections of two directions to invert the 3D image by utilizing voxels to rebuild the spatial structure of the object. In the future, the 3D-VIS will have broad application prospects in medical imaging, virtual reality, industrial automation, and other fields.

Construction of a 3D/2D heterojunction based on a fluorinated cyclohexylamine 2D Ruddlesden–Popper perovskite for highly efficient and stable perovskite solar cells

Nonradiative recombination at perovskite/charge transport layer interfaces is caused by surface defects and instability, and it is known to limit the long-term development of perovskite solar cells (PSCs). To overcome this issue, the three-dimensional/two-dimensional (3D/2D) perovskite heterojunction has emerged as a possible solution to improve the stabilities and efficiency of PSCs. Herein, we employ a simple one-step method to prepare n-i-p-structured PSCs using a 3D/2D perovskite heterojunction as the absorption layer. For this purpose, the large and non-centrosymmetric 4,4-difluorocyclohexylammonium (DFCHA+) cation, which has been confirmed to be a valid organic spacer in 2D Ruddlesden–Popper (RP) phase perovskites, is employed as an organic ligand for post-treatment of the surfaces of MAPbI3 films. The presence of an ultrathin 2D RP phase perovskite was confirmed on the surface, and the 3D/2D perovskite heterojunction was successfully constructed. Benefitting from surface post-treatment, the density of the surface trap states was reduced with effective passivation. In addition, nonradiative recombination was suppressed, and the interface bands were aligned. As a result, the optimal device achieved a power conversion efficiency of 21.93% with a remarkable open-circuit voltage (VOC) of 1.14 V, a current density (JSC) of 23.71 mA cm−2, and a fill factor of 0.82. Furthermore, owing to the hydrophobicity of the DFCHA+ cation, the unencapsulated device was able to maintain an initial efficiency of 82.3% after storage for 500 h at a relative humidity of ∼45%. We believe that this post-treatment strategy has wide application potential in the field of photovoltaic devices.