Ruddlesden-Popper Perovskites Research Articles

Tuning Electronic and Structural Properties of Lead-Free Metal Halide Perovskites: A Comparative Study of 2D Ruddlesden-Popper and 3D Compositions.

In recent decades, two-dimensional (\num{2}D) perovskites have emerged as promising semiconductors for next-generation photovoltaics, showing notable advancements in solar energy conversion. Herein, we explore the impact of alternative inorganic lattice \ce{BX}-based compositions ($\ce{B} = \ce{Ge}$ or \ce{Sn}, $\ce{X} = \ce{Br}$ or \ce{I}) on the energy gap and stability. Our investigation encompasses \ce{BA$_2$MA$_{n-1}$B$_n$X$_{3n+1}$} \num{2}D Ruddlesden-Popper perovskites (for $n = \num{1} - \num{5}$ layers) and \num{3}D bulk \ce{(MA)BX$_3$} systems, employing first-principles calculations with spin-orbit coupling (SOC), DFT-1/2 quasiparticle, and D3 dispersion corrections. The study unveils how atoms with smaller ionic radii induce anisotropic internal and external distortions within the inorganic and organic lattices. Introducing the \ce{BA} spacers in the low-layer regime reduces local distortions but widens band gaps. Our calculation protocol provides deeper insights into the physics and chemistry underlying \num{2}D perovskite materials, paving the way for optimizing environmentally friendly alternatives that can efficiently replace \ce{Pb} with sustainable materials.

Orbital-overlap-driven hybridization in 3d-transition metal perovskite oxides LaMO3 (M = Ti-Ni) and La2CuO4

The wide tunability of strongly correlated transition metal (TM) oxides stems from their complex electronic properties and the coupled degrees of freedom. Among the perovskite oxides family, LaMO3 (M = Ti-Ni) allows an M-dependent systematic study of the electronic structure within the same-structure-family motif. While most of the studies have been focusing on the 3d TMs and oxygen sites, the role of the rare-earth site has been far less explored. In this work, we use resonant inelastic X-ray scattering (RIXS) at the lanthanum N4,5 edges and density functional theory (DFT) to investigate the hybridization mechanisms in LaMO3. We link the spatial-overlap-driven hybridization to energetic-overlap-driven hybridization by comparing the RIXS chemical shifts and the DFT band widths. The scope is extended to highly covalent Ruddlesden-Popper perovskite La2CuO4 by intercalating lanthanum atoms to rock-salt layers. Our work evidences an observable contribution of localized lanthanum 5p and 4f orbitals in the band structure.

Purely Ionically Bonded Cation Paving the Way to Ultralow Thermal Conductivity and Large Thermoelectric Figure of Merit in Ruddlesden-Popper Perovskite Cs2SnI2Br2.

Lower dimensional materials have gained quite a bit of popularity in the last few decades. Perovskite materials have been studied extensively for their photovoltaic properties. But for large scale application of photovoltaic materials, the thermal properties need to be studied. In this work, using first principles calculations, we have studied the thermal conductivity and thermoelectric performance of quasi two-dimensional (2D) Ruddlesden-Popper phase of perovskite, Cs2SnI2Br2. The Cs atoms are found to be ionically bonded to the halogens leading to low elastic constants and hence give rise to weak bonding. The large anharmonicity in this material causes the lattice thermal conductivity to be ultralow having a value of 0.30 W.m-1.K-1 at 300 K and therefore the thermoelectric figure of merit has been found to be high with a maximum value of 2.08 at 600 K. This lead-free 2D perovskite can be the precursor to a wide variety of similar materials with ultralow thermal conductivity.

Vertically Oriented Quasi-2D Perovskite Grown In-Situ by Carbonyl Array-Synergized Crystallization for Direct X-Ray Detectors.

Quasi-2D perovskite quantum wells are increasingly recognized as promising candidates for direct-conversion X-ray detection. However, the fabrication of oriented and uniformly thick quasi-2D perovskite films, crucial for effective high-energy X-ray detection, is hindered by the inherent challenges of preferential crystallization at the gas-liquid interface, resulting in poor film quality. In addressing this limitation, a carbonyl array-synergized crystallization (CSC) strategy is employed for the fabrication of thick films of a quasi-2D Ruddlesden-Popper (RP) phase perovskite, specifically PEA2MA4Pb5I16. The CSC strategy involves incorporating two forms of carbonyls in the perovskite precursor, generating large and dense intermediates. This design reduces the nucleation rate at the gas-liquid interface, enhances the binding energies of Pb2+ at (202) and (111) planes, and passivates ion vacancy defects. Consequently, the construction of high-quality thick films of PEA2MA4Pb5I16 RP perovskite quantum wells is achieved and characterized by vertical orientation and a pure well-width distribution. The corresponding PEA2MA4Pb5I16 RP perovskite X-ray detectors exhibit multi-dimensional advantages in performance compared to previous approaches and commercially available a-Se detectors. This CSC strategy promotes 2D perovskites as a candidate for next-generation large-area flat-panel X-ray detection systems.

High responsivity VIS-NIR photodetector based on (PEA)2PbI4/P3HT Heterojunction

Abstract Two-dimensional (2D) Ruddlesden-Popper (RP) perovskite is an ideal platform for building high-performance photodetectors due to its unique structure, excellent stability, and tunable bandgap. However, 2D perovskite heterojunction photodetectors are still less reported. In this work, the photodetector based on (PEA)2PbI4/P3HT heterojunction was prepared by the liquid-phase solution method under air conditions, which showed a responsivity (R) of 8.38 A/W and a specific detectivity (D*) of 6.53 × 1011Jones under 808 nm light. In addition, the device has a transient response time of 79.57 µs/484 µs and a high stability performance that maintains more than 95% of the photocurrent under continuous cycling tests and shows good cyclic stability after 30 days without encapsulation. This work provides a promising strategy for extending 2D perovskite photodetectors in the VIS to NIR spectral range.

A numerical approach to optimize the efficiency of a novel HTL-free Sr3Ti2S7 Ruddlesden-Popper perovskite solar cell

The exceptional environmental and structural stability of two-dimensional Ruddlesden-Popper perovskites has made them appealing candidates for high-performance perovskite solar cells. Besides, Ruddlesden-Popper perovskites can be synthesized using low-cost solution processing and have tunable bandgaps as compared to their conventional three-dimensional counterparts. Therefore, a Ruddlesden–Popper perovskite solar cell has been reported in this investigation and the SCAPS program has been used to theoretically study the device performance of the proposed lead-free, environmentally friendly perovskite solar cell. A novel Sr3Ti2S7 material has been utilized as the light absorber for the first time in such a theoretical study. Two different configurations, employing WS2 and C60 electron transport layers have been presented and device simulations have been performed to optimize the solar cell. The utilization of C60 as an electron transport material did not prove to be beneficial for the solar cell as it suffered from major recombination losses. It was also found that higher doping concentration of the electron transport materials could help these cells achieve improved fill factor. The diffusion length of the electrons and holes with respect to absorber defect density was also determined. Mott-Schottky analysis proved that the ITO/C60/Sr3Ti2S7/Au structure had a lower flatband potential compared to ITO/WS2/Sr3Ti2S7/Au. Additionally, from the impedance spectroscopy results, the recombination lifetime of the ITO/WS2/Sr3Ti2S7/Au configuration was found to be 46.7 μs compared to only 12.9 μs for the ITO/C60/Sr3Ti2S7/Au architecture. It was also established that if the thickness of the absorber and the bulk defect concentration were optimized the ITO/WS2/Sr3Ti2S7/Au and ITO/C60/Sr3Ti2S7/Au solar cells could achieve conversion efficiencies close to 11.0 % and 10.0 % respectively.

Rational Design of Ruddlesden–Popper Perovskite Ferrites as Air Electrode for Highly Active and Durable Reversible Protonic Ceramic Cells

HighlightsA novel A/B-sites co-substitution strategy was introduced to enhance the performance and durability of Ruddlesden–Popper perovskite Sr3Fe2O7−δ (SF)-based air electrodes for reversible protonic ceramic cells (RePCCs).Simultaneous Sr-deficiency and Nb-substitution in SF result in Sr2.8Fe1.8Nb0.2O7−δ (D-SFN), offering improved structural stability under RePCC conditions by suppressing the formation of Sr3Fe2(OH)12 phase.The introduction of Sr-deficiency enhances oxygen vacancy concentration in D-SFN, promoting efficient oxygen transport within the material and contributing to excellent activity in RePCCs.

Enhanced Photostability of the Colloidal Ruddlesden–Popper Perovskite Nanoplate through 4-Fluorobenzylammonium Iodide-Mediated Surface Engineering for Photoluminescent Application

Enhanced Photostability of the Colloidal Ruddlesden–Popper Perovskite Nanoplate through 4-Fluorobenzylammonium Iodide-Mediated Surface Engineering for Photoluminescent Application

High-quality 2D Ruddlesden-Popper perovskites single crystal and its intrinsic spectral properties

High-quality 2D Ruddlesden-Popper perovskite (RPP) single crystals with large size are highly desirable for fundamental research and different related applications, which also is critical to understand the reported divergent spectral properties of 2D RPP. In this study, we successfully prepared crack free (n-C12H25NH3)2(CH3NH3)Pb2I7 single crystal with a lateral size up to centimeter by regulating the interlayer interaction and aggregate behavior of this layered self-assembly lattice. The RPP crystals show step-like absorbance band with a clear cutoff at 588 nm. The optical band gap was determined as 2.1 eV, which was consistent with previous theoretical calculation results, and clarified its divergent spectral properties. Moreover, a narrow photoluminescence (PL) peak at 623 nm was observed near the band edge. Time-resolved PL measurements revealed a highly reproducible decaying pathway, comprising three distinct components with lifetime as τ1 ∼ 0.57, τ2 ∼ 2.33 ns and τ3 ∼ 11.40 ns respectively. This crystal has demonstrated remarkable long-term chemical stability under ambient conditions.

Optimization Charge-Carrier Properties of 2D Ruddlesden–Popper Perovskite for Solar Cells

Optimization Charge-Carrier Properties of 2D Ruddlesden–Popper Perovskite for Solar Cells

Regulation of Ni/Co Ratio and Gas Transport in High‐Order Ruddlesden–Popper Perovskite Air Electrodes for Protonic Ceramic Electrochemical Cells

AbstractThe delicate design of efficient air electrodes is conducive to improving the reaction kinetics and operational durability of protonic ceramic electrochemical cells (PCECs) at intermediate‐low temperatures. Here, a series of high‐order Ruddlesden–Popper (RP) perovskite electrodes are developed via the regulation of Ni/Co ratio and porosity for efficient charge/gas transfer. As verified by structural analysis and electrochemical characterizations, the electrode with a composition of Pr4Ni1.8Co1.2O10‐δ (PNCO64) shows the most matchable thermal expansion behavior with electrolytes, and highest electrical conductivity, and best catalytic activity toward oxygen reduction/evolution reactions. The Ni/Co ratio of 6:4 can induce the formation of an optimized amount of Pr6O11 in PNCO64, which is likely the pivotal source of the improved catalytic activity. When implemented on PCECs, the PNCO64 electrodes with the addition of 5% graphite pore‐former achieve a remarkable peak power density (1.18 W cm−2) and a high current density of 2.08 A cm−2 at 1.3 V at 600 °C. Excellent durability in fuel cell mode (≈85 h) and electrolysis mode (≈92 h) is also accomplished in PCECs at 600 °C.

An Active and Stable Cobalt‐Free Ruddlesden–Popper Nd0.8Sr1.2Ni1‐xFexO4±δ Air Electrode for Reversible Proton‐Conducting Solid Oxide Cells

AbstractReversible proton‐conducting solid oxide cells (R‐PSOCs) are considered to be one of the most promising devices for efficient power generation and hydrogen production. However, the requirement of high catalytic activity for fast oxygen reduction/evolution reaction (ORR/OER) and durability under high steam concentration of air electrode materials remains the major challenge for the practical application of R‐PSOCs. Here, a series of cobalt‐free Ruddlesden–Popper perovskite of Nd0.8Sr1.2Ni1‐xFexO4±δ are reported with mixed conductivity for enhanced ORR/OER kinetics. The R‐PSOCs with an optimal Nd0.8Sr1.2Ni0.7Fe0.3O4±δ air electrode show a high peak power density of 1.28 W cm−2 in the fuel cell mode and a promising current density of 3.24 A cm−2 at 1.3 V in the electrolysis cell mode at 700 °C. In addition, the R‐PSOCs show favorable stability under the fuel cell, electrolysis, and reversible modes for hundreds of hours. This work demonstrates that the Ruddlesden–Popper materials can be utilized as suitable air electrodes for R‐PSOCs.

Exciton engineering of 2D Ruddlesden–Popper perovskites by synergistically tuning the intra and interlayer structures

Designing two-dimensional halide perovskites for high-performance optoelectronic applications requires deep understanding of the structure-property relationship that governs their excitonic behaviors. However, a design framework that considers both intra and interlayer structures modified by the A-site and spacer cations, respectively, has not been developed. Here, we use pressure to synergistically tune the intra and interlayer structures and uncover the structural modulations that result in improved optoelectronic performance. Under applied pressure, (BA)2(GA)Pb2I7 exhibits a 72-fold boost of photoluminescence and 10-fold increase of photoconductivity. Based on the observed structural change, we introduce a structural descriptor χ that describes both the intra and interlayer characteristics and establish a general quantitative relationship between χ and photoluminescence quantum yield: smaller χ correlates with minimized trapped excitons and more efficient emission from free excitons. Building on this principle, we design a perovskite (CMA)2(FA)Pb2I7 that exhibits a small χ and an impressive photoluminescence quantum yield of 59.3%.

Water-Oil Interfacial Synthesis of Two-Dimensional Colloidal Lead-Iodide Perovskites with Enhanced Efficiency and Stability.

Two-dimensional Ruddlesden-Popper perovskites L2PbI4 (L = alkylammonium cation) (RPPs) have attracted significant attention due to their unique excitonic characteristics. However, their ultrafast reaction dynamics exacerbates the structural distortion of the inorganic framework, leading to severe deterioration in photoluminescence. Here, we propose a water-oil interfacial synthesis approach to achieve controlled growth of the RPPs nanosheets. By segregating Pb and I precursors in two immiscible solvents, the nucleation and growth of RPPs are prolonged to the minute level. L2PbI4 nanosheets terminated with various alkylammonium are synthesized, and the factors influencing the growth kinetics of RPPs nanosheets are investigated. The resulting (PEA)2PbI4 nanosheets exhibit a 3.6-time enhancement in quantum efficiency and 3.2-time improvement photostability compared to those synthesized using the classical recrystallization method. A white light-emitting diode based on (HDA)2PbI4 nanosheets is fabricated, achieving a color gamut of 119.7% of the NTSC display standards. This innovative approach offers a new method for the controlled growth of 2D RPPs with improved optical quality and stability.

Ruddlesden-Popper Perovskite Nanocrystals as Interface Modification Layer for Efficient Perovskite Solar Cells.

Perovskite nanocrystals are advantageous for interfacial passivation of perovskite solar cells (PSCs), but the insulating long alkyl chain surface ligands impede the charge transfer, while the conventional ligand exchange would possibly introduce surface defects to the nanocrystals. In this work, we reported novel in situ modification of CsPbBr3 nanocrystals using a short chain conjugated molecule 2-methoxyphenylethylammonium iodide (2-MeO-PEAI) for interfacial passivation of PSCs. Transmission electron microscopy studies with atomic resolution unveil the transformation from cubic CsPbBr3 to Ruddlesden-Popper phase (RPP) nanocrystals due to halogen exchange. Synergic passivation by the RPP nanocrystals and 2-MeO-PEA+ has led to suppressed interface defects and enhanced charge carrier transport. Consequently, PSCs with in situ modified RPP nanocrystals achieved a champion power conversion efficiency of 24.39%, along with an improvement in stability. This work brings insights into the microstructural evolution of perovskite nanocrystals, providing a novel and feasible approach for interfacial passivation of PSCs.

Boosting MA-based two-dimensional Ruddlesden-Popper perovskite solar cells by incorporating a binary spacer

Two-dimensional Ruddlesden-Popper (2DRP) perovskite exhibits excellent stability in perovskite solar cells (PSCs) due to introducing hydrophobic long-chain organic spacers. However, the poor charge transporting property of bulky organic cation spacers limits the performance of 2DRP PSCs. Inspired by the A-site cation alloying strategy in 3D perovskites, 2DRP perovskites with a binary spacer can promote charge transporting compared to the unary spacer counterparts. Herein, the superior MA-based 2DRP perovskite films with a binary spacer, including 3-guanidinopropanoic acid (GPA) and 4-fluorophenethylamine (FPEA) are realized. These films (GPA0.85FPEA0.15)2MA4Pb5I16 show good morphology, large grain size, decreased trap state density, and preferential orientation of the as-prepared film. Accordingly, the present 2DRP-based PSC with the binary spacer achieves a remarkable efficiency of 18.37% with a VOC of 1.15 V, a JSC of 20.13 mA cm−2, and an FF of 79.23%. To our knowledge, the PCE value should be the highest for binary spacer MA-based 2DRP (n ≤ 5) PSCs to date. Importantly, owing to the hydrophobic fluorine group of FPEA and the enhanced interlayer interaction by FPEA, the unencapsulated 2DRP PSCs based on binary spacers exhibit much excellent humidity stability and thermal stability than the unary spacer counterparts.

Origin of discrete donor–acceptor pair transitions in 2D Ruddlesden–Popper perovskites

Two-dimensional (2D) van der Waals nanomaterials have attracted considerable attention for potential use in photonic and light–matter applications at the nanoscale. Thanks to their excitonic properties, 2D perovskites are also promising active materials to be included in devices working at room temperature. In this work, we study the presence of very narrow and spatially localized optical transitions in 2D lead halide perovskites by μ-photoluminescence and time-decay measurements. These discrete optical transitions are characterized by sub-millielectronvolt linewidths (≃120μeV) and long decay times (5–8 ns). X-ray photoemission and density-functional theory calculations have been employed to investigate the chemical origin of electronic states responsible of these transitions. The association of phenethylammonium with methylammonium cations into 2D Ruddlesden–Popper perovskites, (PEA)2(MA)n−1PbnI3n+1, particularly in phases with n≥2, has been identified as a mechanism of donor–acceptor pair (DAP) formation, corresponding to the displacement of lead atoms and their replacement by methylammonium. Ionized DAP recombination is identified as the most likely physical source of the observed discrete optical emission lines. The analysis of the experimental data with a simple model, which evaluates the Coulombic interaction between ionized acceptors and donors, returns a donor in Bohr radius of the order of ≃10 nm. The analysis of the spectral and electronic characteristics of these single donor–acceptor states in 2D perovskites is of particular importance both from the point of view of fundamental research, as well as to be able to link the emission of these states with new optoelectronic applications that require long-range optically controllable interactions.

Realizing Phase‐Pure (PEA)2FAPb2I7 Perovskite Films by Inhibiting 3D Phase Formation

Abstract2D Ruddlesden–Popper (RP) layered metal‐halide perovskites have garnered significant interest due to their unique photoelectric properties and excellent stability. However, 2D perovskite films prepared via solution process generally exhibit multi‐quantum well structure with random well width distribution, which significantly impedes the carrier transportation. Herein, the synthesis of phase‐pure 2D (PEA)2FAPb2I7 (PEA = C8H11N, FA = CH4N2) perovskite thin films is reported in ambient environment achieved by suppressing the formation of the 3D perovskite phase. First, incorporation of MACl additive can effectively regulate the intermediate during crystallization, facilitating the formation of a metastable 3D MAxFA1‐xPbIyCl3‐y phase. Second, precise control of environmental humidity is employed to further inhibit the formation of α‐FAPbI3 phase. As a result, the perovskite intermediate composed of predominantly metastable 3D phase and 2D n = 2 phase is achieved, which is eventually transformed into 2D n = 2 perovskite during annealing, leading to markedly enhanced phase purity. Photoconductive‐type photodetectors based on the phase‐pure 2D RP perovskite films are fabricated, demonstrating a high detectivity of over 9.4 × 1012 Jones due to the improved carrier transportation. This study provides a comprehensive insight into the crystallization process of phase‐pure 2D perovskites.

Multicomponent doping realized superior triple-conducting within cobalt-free Ruddlesden-Popper-type perovskite for Proton-conducting fuel cells cathode

Proton-conducting solid oxide fuel cells (H-SOFCs) are appealing for low-to-intermediate temperature operation due to their intrinsic lower activation energy and better ionic conductivity. Unfortunately, there are currently few acceptable and high-performing cathode materials available for H-SOFCs. Herein, we present a novel high performance multicomponent Ruddlesden-Popper (RP) type cathode Pr3Ni1.5Cu0.3Nb0.05Ta0.05Zr0.05Y0.05O7-δ (PNCNTZY) with superior triple conducting property. The multicomponent co-doping of Nb, Ta, Zr, and Y brings about the enhancement of configurational entropy and cocktail effect for improving H+/O2-/e- triple conductivity and oxygen vacancy concentration. Naturally, the ORR activity is improved by facilitated charge transfer and oxygen surface exchange, exhibiting reduced polarization resistance to just 0.24 Ω cm2 at 550 °C. When used as the cathode in H-SOFC single cells, excellent power production is demonstrated at 550 °C, with a peak power density of up to 0.84 W cm-2. Furthermore, the PNCNTZY sample shows adequate thermal compatibility with proton conductor electrolytes BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) and then appropriate endurance durability (0.8 A cm-2 at 550 °C for about 250 h) due to their match of thermal expansion coefficient (TEC) brought about by the Co-free and partial replacement of larger-size elements. This extremely promising Co-free RP perovskite cathode for H-SOFCs produced by this work might provide a new type candidate and novel strategy for the commercialization of H-SOFCs.

Impact of large A-site cations on electron-vibrational interactions in 2D halide perovskites: Ab initio quantum dynamics.

Using abinitio nonadiabatic molecular dynamics, we study the effect of large A-site cations on nonradiative electron-hole recombination in two-dimensional Ruddlesden-Popper perovskites HA2APb2I7, HA = n-hexylammonium, A = methylammonium (MA), or guanidinium (GA). The steric hindrance created by large GA cations distorts and stiffens the inorganic Pb-I lattice, reduces thermal structural fluctuations, and maintains the delocalization of electrons and holes at ambient and elevated temperatures. The delocalized charges interact more strongly in the GA system than in the MA system, and the charge recombination is accelerated. In contrast, replacement of only some MA cations with GA enhances disorder and increases charge lifetime, as seen in three-dimensional perovskites. This study highlights the key influence of structural fluctuations and disorder on the properties of charge carriers in metal halide perovskites, providing guidance for tuning materials' optoelectronic performance.