Ruddlesden-Popper Halide Perovskites Research Articles

Nonlinear Absorption in 2D Ruddlesden-Popper Perovskites: Pathways to Ultrafast Optical Applications.

Owing to their distinctive photophysical properties resulting from their larger exciton binding energy and the influence of dielectric and quantum confinement effects, considerable research interest has been directed toward two-dimensional Ruddlesden-Popper halide perovskites (2D RP-HPs). Particularly, 2D RP-HPs exhibit exceptional multiphoton absorption (MPA) effects that reveal versatile applications. In this work, two-photon absorption (2PA) and three-photon absorption (3PA) in 2D RP-HPs, specifically (PEA)2PbBr4 and (BA)2PbBr4 platelets, have been demonstrated through their photoluminescence spectra under multiphoton excitation, revealing a power law relationship with excitation energy. On the other hand, polarization-dependent MPA measurements are also conducted to obtain their anisotropy properties. The excellent 2PA and 3PA effects of 2D RP-HPs have found applications in ultrafast optics to construct fringe-resolved autocorrelation traces, enabling the retrieval of pulse duration not only passively mode-locked Ti:sapphire at 800 nm but also Yb-doped fiber lasers at 1030 nm.

First-Principles Investigation of Optoelectronic Structure and Thermodynamic Properties of Ruddlesden-Popper Halide Perovskites for Optoelectronic Applications

First-Principles Investigation of Optoelectronic Structure and Thermodynamic Properties of Ruddlesden-Popper Halide Perovskites for Optoelectronic Applications

Terahertz emission from two-dimensional Ruddlesden-Popper halide perovskites driven by electric dipole and quadrupole under below-band-gap excitation

Terahertz emission from two-dimensional Ruddlesden-Popper halide perovskites driven by electric dipole and quadrupole under below-band-gap excitation

Investigation of NMR shielding, EFG and structural relaxation of all-inorganic Pb-based Ruddlesden Popper halide perovskites

Investigation of NMR shielding, EFG and structural relaxation of all-inorganic Pb-based Ruddlesden Popper halide perovskites

Emergence of Rashba-/Dresselhaus effects in Ruddlesden–Popper halide perovskites with octahedral rotations

Ruddlesden–Popper halide perovskites are highly versatile quasi-two-dimensional energy materials with a wide range of tunable optoelectronic properties. Here we use the all-inorganic CsPb n X Ruddlesden–Popper perovskites with X = I, Br, and Cl to systematically model the effect of octahedral tilting distortions on the energy landscape, band gaps, macroscopic polarization, and the emergence of Rashba-/Dresselhaus splitting in these materials. We construct all unique n = 1 and n = 2 structures following from octahedral tilts and use first-principles density functional theory to calculate total energies, polarizations and band structures, backed up by band gap calculations using the GW approach. Our results provide design rules for tailoring structural distortions and band-structure properties in all-inorganic Ruddlesden–Popper perovskites through the interplay of the amplitude, direction, and chemical character of the antiferrodistortive distortion modes contributing to each octahedral tilt pattern. Our work emphasizes that, in contrast to three-dimensional perovskites, polar structures may arise from a combination of octahedral tilts, and Rashba-/Dresselhaus splitting in this class of materials is determined by the direction and Pb-I orbital contribution of the polar distortion mode.

Band gap engineering and optoelectronic properties of all-inorganic Ruddlesden-Popper halide perovskites Cs2B(X1-uYu)4 (B = Pb, Sn; X/Y = Cl, Br, I)

In this article two-dimensional Ruddlesden-Popper (2DRP) halide perovskites Cs2B(X1-uYu)4 where B = Pb, Sn; X/Y = Cl, Br, I; and u = 0, 0.25, 0.5, 0.75, 1 are investigated for potential applications in optoelectronic, photoemission and photovoltaic devices. In these compounds the corner sharing B-centered [BX2Y4]4- units build the 2D [BX2Y2]n2n− plane, where the halides occupy the in-plane bridging and out of plane apical site respectively, while the spacer cation (Cs+) balancing the charge and separate the octahedral layers. These compounds have direct band gaps and spin orbit (SOC) calculations split Pb/Sn p-orbital and reduce the band gaps. The wide (1.04–3.45) and direct band gaps enable these materials for futuristic applications in optoelectronics, high speed ultrathin transistors and photodetectors. The anti-bonding lone-pair Pb/Sn-s orbital at the valence band edge is excellent for light absorption and photovoltaic performance. These compounds are good dielectric and optically functional materials for photovoltaic and energy storage devices due to their small values of charge carrier effective masses and large exciton binding energies. Therefore, the optical coefficients like dielectric function (real and imaginary), absorption coefficient and index of refraction are calculated.

Structural and optoelectronic properties of Ge- and Si -based inorganic two dimensional Ruddlesden Popper halide perovskites

In the present work silicon (Si) and germanium (Ge) based two dimensional Ruddlesden-Popper halide perovskites (2DRP-HPs) Cs 2 BX 2 Y 2 (B = Ge/Si and X/Y= Cl/Cl, Br/Cl, I/Cl, Br/Br, I/Br and I/I) are studied for photovoltaic, visible emitter and other potential optoelectronic applications. The tolerance factor values of these compounds are greater than one and hence exist in the stable K 2 NiF 4 -type tetragonal structure. The direct band gaps (1.39-2.59 eV) make these compounds important for futuristic applications in optoelectronic devices operational in the visible region of the electromagnetic spectrum, photodetectors and high speed ultrathin transistors. The spin orbit coupling (SOC) effect increases from Cl to I and splits the p-orbital of halogen in the conduction band, due to which the band gap reduces. The small exciton binding energies, effective masses of charge carrier, enable these materials for energy storage and photovoltaic applications. At visible and ultraviolet energy range, these RP-HPs have excellent response to the incident photons, which confirms their commercialization in optoelectronic devices and photovoltaic cells.

Direct Characterization of Type‐I Band Alignment in 2D Ruddlesden–Popper Perovskites

Abstract2D Ruddlesden–Popper halide perovskites have attracted considerable attention due to their desirable optoelectronic properties, high chemical and structural tunability, and improved environmental stability. However, the understanding of their structure–properties relationships is still limited. In particular, the energy level positions and band alignments at interfaces involving these materials, which are important features to control in the context of any applications, are still under debate. Here, the electronic structure of high‐purity films of BA2MAn−1PbnI3n+1 for n = 1–5 (where BA stands for butylammonium and MA for methylammonium) is investigated, using optical absorption, ultraviolet, and inverse photoemission spectroscopies, and density functional theory calculations. This study determines the ionization energy and electron affinity of each compound and demonstrates a type‐I band alignment for the BA2MAn−1PbnI3n+1 series. This study further describes the evolution of the exciton binding energy as a function of the thickness of the inorganic layers.

Enhanced Amplified Spontaneous Emission in Quasi-2D Perovskite by Facilitating Energy Transfer.

Despite the superior optoelectronic properties of quasi-two-dimensional (quasi-2D) Ruddlesden-Popper halide perovskites, the inhomogeneous distribution of mixed phases result in inefficient energy transfer and multiple emission peaks. Herein, the insufficient energy funneling process at the high-energy phase is almost completely suppressed and the excitonic understanding of gain nature is studied in the energy funneling managed quasi-2D perovskite via introducing poly(vinyl pyrrolidone) (PVP) additive. The energy transfer process is facilitated from 0.37 to 0.26 ps after introducing the PVP additive, accelerating the exciton accumulation in the emissive state, and increasing the ratio of the high-dimensional phase for enhancing radiative emission. The gain lifetime is promoted to be as fast as 28 ps to outcompete nonradiative recombination during the build-up of population inversion. Simultaneously, the net gain coefficient is increased by more than twofold that of the pristine perovskite film. Owing to the remarkable gain properties, room-temperature amplified spontaneous emission is realized with a low threshold of 11.3 μJ/cm2, 4 times lower than 43 μJ/cm2 of the pristine film. Our findings suggest that the PVP-treated quasi-2D perovskite shows great promise for high-performance laser devices.

Stabilized High-Membered and Phase-Pure 2D All Inorganic Ruddlesden-Popper Halide Perovskites Nanocrystals as Photocatalysts for the CO2 Reduction Reaction.

In contrast to the 2D organic-inorganic hybrid Ruddlesden-Popper halide perovskites (RPP), a new class of 2D all inorganic RPP (IRPP) has been recently proposed by substituting the organic spacers with an optimal inorganic alternative of cesium cations (Cs+ ). Nevertheless, the synthesis of high-membered 2D IRPPs (n>1) has been a very challenging task because the Cs+ need to act as both spacers and A-site cations simultaneously. This work presents the successful synthesis of stable phase-pure high-membered 2D IRPPsof Csn+1 Pbn Br3n+1 nanosheets (NSs) with n= 3 and 4 by employing the strategy of using additional strong binding bidentate ligands. The structures of the 2D IRPPs (n= 3 and 4) NSs are confirmed by powder X-ray diffraction and high-resolution aberration-corrected scanning transmission electron microscope measurements. These 2D IRPPs NSs exhibit a strong quantum confinement effect with tunable absorption and emission in the visible light range by varying their n values, attributed to their inherent 2D quantum-well structure. The superior structural and optical stability of the phase-pure high-membered 2D IRPPs make them a promising candidate as photocatalysts in CO2 reduction reactions with outstanding photocatalytic performance and long-termstability.

Ion migration mechanism in all-inorganic Ruddlesden-Popper lead halide perovskites by first-principles calculations.

Ion migration under light illumination or electric field could cause several complex phenomena, such as hysteresis, phase segregation, and interface passivation, in optoelectronic devices based on hybrid organic-inorganic perovskites. The high ionic conductivity of metal halide perovskites can be ascribed to the lower migration barrier of halide anions, which has been demonstrated to be inhibited by the large organic layer of two-dimensional perovskite structures. However, in all-inorganic two-dimensional perovskites, the diffusion mechanism of halide anions has not been comprehensively studied. Herein, we investigate the diffusion mechanism of halide anions in all-inorganic Ruddlesden-Popper (RP) halide perovskites by first-principles calculations. In these all-inorganic perovskites, the inorganic CsI layer can also prevent halide diffusion between the adjacent octahedral slabs via the vacancy-hopping mechanism. However, intercalation provides an additional diffusion channel for halide interstitials, which promote in-plane diffusion in RP perovskites. These results reveal the migration properties of halide vacancies and interstitials in all-inorganic RP perovskites, which would be beneficial for exploring their novel optoelectronic applications.

Atomically Resolved Quantum-Confined Electronic Structures at Organic-Inorganic Interfaces of Two-Dimensional Ruddlesden-Popper Halide Perovskites.

This work demonstrates the direct visualization of atomically resolved quantum-confined electronic structures at organic-inorganic heterointerfaces of two-dimensional (2D) organic-inorganic hybrid Ruddlesden-Popper perovskites (RPPs); this is accomplished with scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) by using solvent engineering to prepare perpendicularly oriented 2D RPPs. Atomically resolved band mapping images across the organic-inorganic interfaces of 2D RPPs yield typical quantum-well-like type-I heterojunction band alignment with band gaps depending on the thicknesses or n values of the inorganic perovskite slabs. The presence of edge states within the band gap due to organic cation vacancies is also observed. In addition, real-space visualization of atomic-scale structural phase transition behavior and changes in local electronic band structures are obtained simultaneously. Our results provide an unequivocal observation and explanation of the quantum-confined electronic structures formed at organic-inorganic interfaces of 2D RPPs.

Anion Exchange of Ruddlesden-Popper Lead Halide Perovskites Produces Stable Lateral Heterostructures.

Heterostructures of three-dimensional (3D) halide perovskites are unstable because of facile anion interdiffusion at halide interfaces. Two-dimensional (2D) Ruddlesden-Popper halide perovskites (RPPs) show suppressed and anisotropic ion diffusion that could enable stable RPP heterostructures, yet the direct and general growth of lateral RPP heterostructures remains challenging. Here, we show that halide miscibility in RPPs decreases with perovskite layer thickness (n), enabling the formation of sharp halide lateral heterostructures from n = 1 and 2 RP lead iodide microplates via anion exchange with hydrogen bromide vapor. In contrast, RPPs with n ≥ 3 form more diffuse lateral heterojunctions, more similar to those in 3D perovskites. The anion exchange behaviors are further modulated by the spacer and A-site cations in the RPP structures. These new insights, and kinetic studies of the exchange reactions, enable the preparation of lateral heterostructures from various n = 2 RPPs that are more stable against anion interdiffusion and degradation for potential optoelectronic device applications.

Layer number dependent exciton dissociation and carrier recombination in 2D Ruddlesden–Popper halide perovskites

Different dynamics of excitons and free carriers in 2D Ruddlesden–Popper halide perovskites with layer numbers of n = 1 and n ≥ 2.

Deterministic fabrication of arbitrary vertical heterostructures of two-dimensional Ruddlesden-Popper halide perovskites.

Ruddlesden-Popper lead halide perovskites have emerged as a new class of two-dimensional semiconductors with tunable optoelectronic properties, potentially offering unlimited heterostructure configurations for exploration. However, the practical realization of such heterostructures is challenging because of the difficulty in achieving controllable direct synthesis or van der Waals integration of halide perovskites due to their mobile and fragile crystal lattices. Here we report direct growth of large-area nanosheets of diverse phase-pure Ruddlesden-Popper perovskites with thicknesses down to one monolayer at the solution-air interface and a reliable approach for gently transferring and stacking these nanosheets. These advances enable the deterministic fabrication of arbitrary vertical heterostructures and multi-heterostructures of Ruddlesden-Popper perovskites with greater structural degrees of freedom that define the electronic structures of the heterojunctions. Such rationally designed heterostructures exhibit interesting interlayer properties, such as interlayer carrier transfer and reduction of the photoluminescence linewidth, and could enable the exploration of exciton physics and optoelectronic applications.

Rashba band splitting in two-dimensional Ruddlesden–Popper halide perovskites

Due to the presence of heavy elements and the dynamic nature of hybrid halide perovskites, the strong spin–orbit coupling effect can give rise to Rashba band splitting in these materials. Despite many reports on the Rashba effect in 3D perovskites like CH3NH3PbI3, little is known about its presence in two-dimensional Ruddlesden–Popper (2DRP) perovskites. In this work, we use first-principle calculations to investigate the magnitude and origin of the Rashba effect in three families of 2DRP perovskites. We demonstrate the correlation between the splitting magnitude and the octahedron distortions. Moreover, different numbers of inorganic layers, spacer cations, and A-site cations have a great influence on the Rashba splitting through different mechanisms. While structures with C6H5C2H4NH3 (PEA) have a significant Rashba splitting only in the monolayer condition, C4H9NH3 (BA) induces large distortion by tilting the CH3NH3 (MA) cations around all octahedrons, giving rise to a larger Rashba splitting with an increasing number of inorganic layers. Our work elucidates the magnitude and origin of the Rashba splitting in 2DRP perovskites and provides guidelines for the manipulation of the Rashba splitting in these materials.

Efficient Energy Funneling in Quasi-2D Perovskites: From Light Emission to Lasing.

Quasi-2D Ruddlesden-Popper halide perovskites with a large exciton binding energy, self-assembled quantum wells, and high quantum yield draw attention for optoelectronic device applications. Thin films of these quasi-2D perovskites consist of a mixture of domains having different dimensionality, allowing energy funneling from lower-dimensional nanosheets (high-bandgap domains) to 3D nanocrystals (low-bandgap domains). High-quality quasi-2D perovskite (PEA)2 (FA)3 Pb4 Br13 films are fabricated by solution engineering. Grazing-incidence wide-angle X-ray scattering measurements are conducted to study the crystal orientation, and transient absorption spectroscopy measurements are conducted to study the charge-carrier dynamics. These data show that highly oriented 2D crystal films have a faster energy transfer from the high-bandgap domains to the low-bandgap domains (<0.5 ps) compared to the randomly oriented films. High-performance light-emitting diodes can be realized with these highly oriented 2D films. Finally, amplified spontaneous emission with a low threshold 4.16 µJ cm-2 is achieved and distributed feedback lasers are also demonstrated. These results show that it is important to control the morphology of the quasi-2D films to achieve efficient energy transfer, which is a critical requirement for light-emitting devices.

Tunable Ferroelectricity in Ruddlesden-Popper Halide Perovskites.

Ruddlesden-Popper (RP) halide perovskites are the new kids on the block for high-performance perovskite photovoltaics with excellent ambient stability. The layered nature of these perovskites offers an exciting possibility of harnessing their ferroelectric property for photovoltaics. Adjacent polar domains in a ferroelectric material allow the spatial separation of electrons and holes. Presently, the structure-function properties governing the ferroelectric behavior of RP perovskites are an open question. Herein, we realize tunable ferroelectricity in 2-phenylethylammonium (PEA) and methylammonium (MA) RP perovskite (PEA)2(MA) n̅-1Pb n̅I3 n̅+1. Second harmonic generation (SHG) confirms the noncentrosymmetric nature of these polycrystalline thin films, whereas piezoresponse force microscopy and polarization-electric field measurements validate the microscopic and macroscopic ferroelectric properties. Temperature-dependent SHG and dielectric constant measurements uncover a phase transition temperature at around 170 °C in these films. Extensive molecular dynamics simulations support the experimental results and identified the correlated reorientation of MA molecules and ion translations as the source of ferroelectricity. Current-voltage characteristics in the dark reveal the persistence of hysteresis in these devices, which has profound implications for light-harvesting and light-emitting applications. Importantly, our findings disclose a viable approach for engineering the ferroelectric properties of RP perovskites that may unlock new functionalities for perovskite optoelectronics.

Pressure-Induced Broadband Emission of 2D Organic-Inorganic Hybrid Perovskite (C6H5C2H4NH3)2PbBr4.

2D Ruddlesden–Popper halide perovskites, which incorporate hydrophobic organic interlayers to considerably improve environmental stability and optical properties diversity, have attracted substantial research attention for optoelectronic applications. The burgeoning broad emission arising from exciton self‐trapping of 2D perovskites shows a strong dependence on a deformable structure. Here, the pressure‐induced broadband emission of layered (001) Pb‐Br perovskite with a large Stokes shift in the visible region is observed by finely improving lattice distortion to increase exciton–phonon coupling under hydrostatic pressure. Band gap narrows ≈0.5 eV under modest pressure, mainly due to the large compressibility of the orientational organic layer, confirming that the bulky organic cations notably influence the structure and, in turn, the various properties of materials. Sequential amorphization of the organic and inorganic layer is confirmed by high pressure Raman and X‐ray diffraction measurements, suggesting the particularity of layered crystal structures. The mechanism constructed here offers a new route for tuning the optical properties of 2D perovskites.

Scaling law for excitons in 2D perovskite quantum wells

Ruddlesden–Popper halide perovskites are 2D solution-processed quantum wells with a general formula A2A’n-1MnX3n+1, where optoelectronic properties can be tuned by varying the perovskite layer thickness (n-value), and have recently emerged as efficient semiconductors with technologically relevant stability. However, fundamental questions concerning the nature of optical resonances (excitons or free carriers) and the exciton reduced mass, and their scaling with quantum well thickness, which are critical for designing efficient optoelectronic devices, remain unresolved. Here, using optical spectroscopy and 60-Tesla magneto-absorption supported by modeling, we unambiguously demonstrate that the optical resonances arise from tightly bound excitons with both exciton reduced masses and binding energies decreasing, respectively, from 0.221 m0 to 0.186 m0 and from 470 meV to 125 meV with increasing thickness from n equals 1 to 5. Based on this study we propose a general scaling law to determine the binding energy of excitons in perovskite quantum wells of any layer thickness.