Ruddlesden-Popper Research Articles

Modification of the band gap of Ruddlesden‒Popper perovskites Srn+1TinO3n+1 (n=1, 2, 3, and ∞) by Fe ion irradiation doping

Ruddlesden‒Popper (RP)-type perovskite materials Srn+1TinO3n+1 (n = 1, 2, 3, and ∞) have important application prospects in photocatalysis. However, their wide band gap limits their visible light absorption ability. Doping is an efficient method that can be used to reduce the band gap and improve its light absorption range. In this work, irradiation doping with the advantages of compulsivity and controllability, rather than a chemical doping method, is used to manipulate the band gaps of Srn+1TinO3n+1 to understand the respective contributions of the substitution of the Sr and Ti sites to the band gap reduction as a function of the n value. The solid-state reaction-prepared RP-type perovskites Srn+1TinO3n+1 (n = 1, 2, 3, and ∞) irradiated by a 270 keV Fe ion beam with 0–1 × 1016 ions/cm2 doses were characterized by SEM, XRD and UV–vis diffuse reflectance spectra. Tauc plot analysis showed that the band gaps of Srn+1TinO3n+1 decreased with an increase in Fe doping dose, which was confirmed by DFT calculations. Meanwhile, the effects of the perovskite and rock-salt layers of the RP-type perovskite on the band gap modification were demonstrated, showing that the band gap of Srn+1TinO3n+1 with smaller n values decreases less when the Fe irradiation dose increases. This is explained by more salt SrO layers found in Srn+1TinO3n+1 for smaller n values, which prevents the substitution of Sr and Ti atoms in perovskite layers, significantly influencing the band gap.

Quasi-2D Ruddlesden-Popper Lead Halide Perovskites: How Edge Matters.

A band-mapping technique is introduced to investigate the formation of low-energy edge states in quasi-2D Ruddlesden-Popper (RP) perovskites, (BA)2(MA)n-1PbnI3n+1, through a localized mode of measurement, namely, scanning tunneling spectroscopy. The local band structures measured at different points reveal the formation of 3D CH3NH3PbI3 (MAPbI3) at the edges of the perovskite nanosheets; for thin films, the 3D phase (n = ∞) could be seen to form at grain boundaries. The presence of MAPbI3 at the edges or grain boundaries of the perovskites has led to self-forming type-II band alignment in BA2MA2Pb3I10 (n = 3). The rationale behind achieving a high-efficiency solar cell based on the material, which has a large exciton binding energy, has been inferred. Kelvin probe force microscopy studies under illumination have yielded a higher surface photovoltage at the edges compared to the interior and supported the inference of exciton dissociation due to internal type-II band alignment in the quasi-2D RP perovskites.

Structural Dimensionality Dependence of the Band Gap in An+1BnX3n+1 Ruddlesden-Popper Perovskites: A Global Picture.

Dimensionality engineering in An+1BnX3n+1 Ruddlesden-Popper (RP) perovskites has recently emerged as a promising tool for tuning the band gap to improve optoelectronic properties. However, the evolution of the band gap is dependent on the material; distinguishing the effects of different factors is urgently needed to guide the rational design of high-performance materials. Through first-principles calculations, we perform a systematic investigation of RP oxide, chalcogenide, and halide perovskites. The results reveal that in addition to the confinement effect and the change in octahedral rotation motions and/or amplitudes, interfacial rumpling and a change in the A-site cation coordination number also determine the evolution of the band gap. More importantly, we emphasize that the evolution of the band gap in RP perovskites is not dependent on the material family. Instead, the B-site frontier orbital type (s, p, and d) and bandwidth, A-site cation, interfacial rumpling, and structural distortions simultaneously determine the evolution of the band gap. These insights enable a complete and deeper understanding of various experimental observations.

Chemically inducing room temperature spin-crossover in double layered magnetic refrigerants Pr1.4+Sr1.6-Mn2O7 (0.0 ≤ x ≤ 0.5)

The height of total entropy (ST) for a magnetic refrigerant material is essentially concerned with the magnetic and structural transitions. However, the participation of such transitions in layered materials is not well understood. Therefore, the purpose of this work is to investigate the interplay between double layer lattice with their single perovskite counterpart, to achieve optimal magnetocaloric performance. A series of self-doped Pr1.4+xSr1.6-xMn2O7 (0.0 ≤ x ≤ 0.5) Ruddlesden-Popper (R-P) perovskite have been prepared through the solid-state sintering method. With increasing the Pr-stoichiometry, the lattice faults have increased and the double layer lattice dramatically disintegrates into single perovskite structure. Due to the reduction of bilayer R-P phase into single perovskite the spin crossover occurs from weak bilayer (TC = 304 K) interactions towards the strong three-dimensional (TC = 308 K) interactions respectively. This series consistently develops thermomagnetic irreversibility in zero-field cooled (ZFC)-field cooled (FC) magnetization, which is indicative of a spin-glass state. The glassy nature has been ascribed collectively to the lattice strain produced because of dislocations and to an antiferromagnetic phase segregated at the surface. The maximum value of temperature average entropy change (TEC) and adiabatic temperature (ΔTad) has enhanced nearly by 4 folds from 0.53 J kg−1 K−1, 0.59 K (for x = 0.0) up to 1.85 J kg−1 K−1, 10 K (for x = 0.5) at 2.5 T, respectively. Additionally, the room temperature relative cooling power has improved from 26.94 J/kg up to 77.84 J/kg with an applied field of 2.5 T. Our findings in this work suggest that the controlled reduction of double layer lattice into single perovskite and/or existence of both phases simultaneously in bilayer R-P manganites may be very effective in obtaining the desirable characteristics of magnetocaloric effects.

25.2: High Detectivity Perovskite‐IGZO Phototransistor with Tunable Photoconductive Gain

Organic‐inorganic hybrid perovskite is a highly light sensitive photodetector material(1), which has competitive advantages of low cost, wide and adjustable light absorption range. However, due to its solubility in polar solvent, its fabrication is not compatible with conventional photolithography process, which limits its application as pixel element in high‐resolution image sensors. Therefore, the patterning of perovskite turns out to be a key issue for practical application of perovskite photodetectors in the field of image sensor(2). In this study, we report a Ruddlesden‐Popper (RP) quasi‐two‐dimensional (quasi‐2D) perovskite ‐ indium gallium zinc oxide (IGZO) phototransistor, and their patterning techniques. A patterned quasi‐2D perovskite layer is deposited on the channel region of IGZO thin film transistor (TFT), which enables ultralow off‐state dark currents of 10−11 A and a high responsivity of 103.5 A/W under 400 nm light illumination with tunable photoconductive gain.

Cesium-doped Dion-Jacobson 2D perovskites for highly stable photovoltaics with an 18.3% efficiency

Dion-Jacobson (DJ) phase 2D layered perovskites have recently emerged as promising candidates for tackling unstable issue of perovskite solar cells (PSCs) owing to their outstanding stability compared to widely studied Ruddlesden-Popper (RP) 2D and 3D analogues. To further improve the efficiency and stability of DJ 2D PSCs, we herein report a series of cesium-doped DJ 2D perovskites (PDA)Csx(MA)3−xPb4I13 (PDA=1,3-propanediammonium) and investigate Cs doping effects on material properties and device performances. The 5% Cs-doped DJ 2D PSC delivers a maximum efficiency of 18.30%, higher than the counterpart without Cs doping. Moreover, unencapsulated devices are remarkably stable, retaining ∼95% of initial efficiencies under continuous one-sun illumination for 5000 h, damp heat at 85 °C & 85% relative humidity for 240 h, and MPP tracking for 1000 h. The excellent efficiency and stability are ascribed to improved film morphology and crystallographic orientation, longer charge carrier lifetime, and reduced nonradiative recombination, induced by the Cs doping. This work demonstrates that doping Cs into DJ 2D perovskites is a facile and effective strategy towards efficient and extremely stable 2D PSCs.

High-Performance van der Waals Photodetectors Based on 2D Ruddlesden–Popper Perovskite/MoS2 Heterojunctions

Perovskites have prevailed in the field of photovoltaics over the past several years thanks to their outstanding optoelectronic properties. Compared to three-dimensional (3D) perovskites, the emerging two-dimensional (2D) Ruddlesden–Popper (RP) phase perovskites have demonstrated superior stability due to their hydrophobic organic capping ligands, which can protect the inside inorganic octahedrons against moisture. Meanwhile, RP perovskites broaden the family of 2D materials, enriching the building blocks for van der Waals heterostructures. Here, we first demonstrated a vertical heterojunction incorporating RP perovskite (C6H5C2H4NH3)2PbBr4 and MoS2. The heterojunction photodetector exhibits an extremely low dark current down to 0.1 pA, which can be attributed to the combining effect of the low carrier density in RP perovskites and the band structure of the heterojunction. The spatially resolved scanning photocurrent microscopy (SPCM) was carried out to confirm the charge transport mechanism and band alignment of the heterojunction. Moreover, the photodetector benefits from the heterojunction structure, leading to a high photoresponsivity (7.98 mA W–1). In addition, the device can be operated under a self-driven mode with a responsivity of 0.168 mA W–1. Our work proves the compatibility of RP perovskites in van der Waals devices, promising a scalable pathway to further applications.

Modifying the optical emission of two-dimensional Ruddlesden-Popper perovskites by laser irradiation

Two-dimensional (2D) organic–inorganic hybrid perovskites, especially Ruddlesden-Popper (RP) perovskites, have attracted great interest in recent years due to their potential applications in the fields of optoelectronics and photovoltaics. In this work, the effects of laser irradiation on the optical emission of a PEA2MA2Pb3I10 thin film (PTF) were systematically investigated by using 488-nm continuous wave laser light and 400-nm femtosecond laser light as the excitation sources. It was found that the photoluminescence (PL) intensity of a PTF increases rapidly with irradiation time and becomes saturated after some time, which is ascribed to the passivation of the defects near the surface of the PTF through the interaction with oxygen. A large redshift of the PL wavelength from ∼ 625 to ∼ 750 nm was realized by simply increasing the laser power. It was suggested that the decomposition of PEA2MA2Pb3I10 into MAPbI3 is responsible for this behavior. The excitation efficiency was improved while the threshold laser power for the decomposition was lowered by constructing a particle-on-film system with a silica microsphere. In this way, the blueshift of the PL wavelength from ∼ 750 to ∼ 520 nm, which is attributed to the further decomposition of MAPbI3 into PbI2, was achieved. Our findings provide a simple and effective way for modifying the optical emission of 2D perovskites and pave the way for realizing photonic devices based on 2D perovskites.

Liquid-Phase van der Waals Epitaxy of a Few-Layer and Unit-Cell Thick Ruddlesden-Popper Halide Perovskite.

2D Ruddlesden-Popper (RP) halide perovskites with natural multiple quantum well structures are an ideal platform to integrate into vertical heterostructures, which may introduce plentiful intriguing optoelectronic properties that are not accessible in a single bulk crystal. Here, we report liquid-phase van der Waals epitaxy of a 2D RP hybrid perovskite (4,4-DFPD)2PbI4 (4,4-DFPD is 4,4-difluoropiperidinium) on muscovite mica and fabricate a series of perovskite-perovskite vertical heterostructures by integrating it with a second 2D RP perovskite R-NPB [NPB = 1-(1-naphthyl)ethylammonium lead bromide] sheets. The grown (4,4-DFPD)2PbI4 nanobelt array can be multiple layers to unit-cell thin and are crystallographically aligned on the mica substrate. An interlayer photo emission in this R-NPB/(4,4-DFPD)2PbI4 heterostructure with a lifetime of about 25 ns at 120 K has been revealed. Our demonstration of epitaxial (4,4-DFPD)2PbI4 array grown on mica via liquid-phase van der Waals epitaxy provides a paradigm to prepare orderly distributed 2D RP hybrid perovskites for further integration into multiple heterostructures. The discovery of a new interlayer emission in the R-NPB/(4,4-DFPD)2PbI4 heterostructure enriches the basic understanding of interlayer charge transition in halide perovskite systems.

Methylamine‐Assisted Preparation of Ruddlesden‐Popper Perovskites for Stable Detection and Imaging of X‐Rays

AbstractSensitive and stable X‐ray detectors are essential for medical diagnostics, nondestructive industrial inspection, and security inspection. Halide perovskite X‐ray detectors are promising for direct X‐ray detection because of their high sensitivity and low limit of detection (LoD). However, their high and unstable dark current, caused by notorious ion migration in hybrid perovskites, limits their performance and long‐term operation stability. Moreover, it is still challenging to prepare high‐quality perovskite with millimeter‐thickness at a large‐scale. In this paper, solid–liquid transition of two‐dimensional (2D) Ruddlesden‐Popper (RP) perovskites enabled by methylamine gas (CH3NH2) is first reported. Based on this novel approach, dense RP perovskite films with tunable ion migration and superior electronic features are produced using a lamination process. The tradeoff between stability and detection performance of perovskite X‐ray detectors is successfully solved by tuning the quantum well width of RP perovskites. X‐ray detectors with a sensitivity of 5362.3 µC Gyair−1 cm−2, LoD of 8.1 nGyair s−1 and highly working stability are achieved simultaneously. Furthermore, single gamma photon detection is realized in the RP perovskite detectors, which further confirms their capability for detecting radiation at ultralow dose rates. This study paves the way for adopting polycrystalline RP perovskites in stable X‐ray detectors.

Building Efficient and Durable Hetero‐Interfaces on a Perovskite‐Based Electrode for Electrochemical CO2 Reduction

AbstractSolid oxide electrochemical cells (SOECs) have demonstrated the potential to be highly efficient devices for electrochemical CO2 reduction (CO2R) at intermediate temperatures. However, the performance and widespread applications for CO2R largely hinge on the sluggish reaction kinetics and poor durability of the state‐of‐the‐art electrodes. Here, the findings in enhancing the reaction activity and durability of a perovskite‐based electrode are reported, Sr2Fe1.5Mo0.3Cu0.2O6‐δ (SF1.5MC), for electrochemical oxidation of H2 and reduction of CO2. Under typical operating conditions, the SF1.5MC electrode is elegantly reconstructed into three phases of oxygen vacancy‐rich double perovskite (DP), Ruddlesden‐popper (RP), and Cu‐Fe metals, as confirmed by X‐ray diffraction and scanning transmission electron microscopy. When applied as a fuel electrode for an electrolyte‐supported SOEC, decent performances are demonstrated at 800 °C, showing a maximum power density of 1.51 W cm−2 in fuel cell mode (on H2 fuel) and a current density of 1.94 A cm−2 at 1.4 V in electrochemical CO2R to CO with high Faradaic efficiencies of ≈100% and good durability.

Transition metal oxide-based membranes for oxygen separation

Tonnage oxygen production is still mostly based on the traditional technology of cryogenic distillation, a century-old, capital- and energy-intensive method. It is critical to create a novel low-cost, energy-efficient approach that can meet the growing demand for oxygen in industry from the clean environmental or energy standpoint. Ruddlesden-Popper (RP) perovskite like oxides -based ionic transport membranes for the oxygen transport have recently been developed as a possible replacement for the traditional cryogenic approach. In this work, we detailly reviewed the progress of RP perovskite oxides based membranes for oxygen transport from separation mechanism, material types, synthesis methods to the final separation performance. This work advances the development of RP perovskite membranes for oxygen transport.

Performance and stability enhancement of mixed dimensional bilayer inverted perovskite (BA2PbI4/MAPbI3) solar cell using drift-diffusion model

A variety of classic photovoltaic technologies, such as multi-crystal silicon and copper indium gallium selenide, have been exceeded by organometal halide perovskite solar cells, which have made significant advancements in the cost-effective manufacturing method as well as the high power conversion efficiency. Meanwhile, the unfavourable operational stability of perovskite solar cells is impeding the commercialization of the technology. When exposed to critical environmental factors such as rising moisture and intense sunlight, perovskite solar cells suffer lattice degradation and lose their ability to harvest energy. As a result, enhancing the stability of perovskite cells is one of the most important variables in determining the next wave of progress for the technology. While there have been numerous techniques reported to improve the stability of perovskite-based photovoltaic cell, the construction of a more than one dimension (2D/3D) perovskite as the light absorbing layer has recently emerged as one of the most reliable strategies to stabilise the perovskite-based device without compromising photo physical performance. Herein, we have computationally simulated p-i-n device configuration composed of ITO/NiO/2D perovskite/3D perovskite/PCBM/Au. The Ruddlesden-Popper (RP) phases of two-dimensional perovskite act as a cover layer, which inhibits the deterioration of 3D perovskite in an open-air environment. Both optical and electrical simulation is performed using solar cell capacitance simulator (SCAPS). Simulation findings showed that the enhancements in overall performance are due to the decrease in the trap state's density and better coordination of the band between the 2D/3D perovskite and the hole-transporting materials. Effects of the interfacial defects (2D perovskite/HTL and 3D perovskite/ETL) on solar cell parameters are also performed. Simulation results reveal that the defects at 3D perovskite/ETL interfacial are more dominating in overall performance degradation. Parametric differences, such as thickness of various layers, standard solar spectra, further refine the proposed architecture. The multidimensional-based architecture proposed in this work resulted in a power conversion efficiency (PCE) of 19.6%.

Space‐Resolved Photoresponse in Quasi‐Two‐Dimensional Ruddlesden–Popper Perovskites

AbstractQuasi‐two‐dimensional (quasi‐2D) organic–inorganic hybrid perovskites have shown excellent ambient stability with decent photovoltaic performance. Further improvement of device level properties requires a comprehensive understanding of the performance‐limiting mechanisms such as phase segregation, ion/electron coupling conduction, and their effects on charge transport at both the micro‐ and macro‐scale. Here, space resolved investigations of Ruddlesden–Popper (RP) phases of the commonquasi‐2D perovskite are probed using two complementary methods, conducting atomic force microscopy (c‐AFM) and Kelvin probe force microscopy (KPFM). Bias‐driven photocurrent mappings obtained by c‐AFM measurements disclose local inhomogeneous conduction and hysteresis currents in quasi‐2D RP perovskites, while relatively uniform conductivity is observed on individual grains. Bias‐driven KPFM reveals that the surface average photovoltage sign is dominated by the band bending at the buried perovskite–substrate interface. The quasi‐2D RP film exhibits substantial variations in the spatial response of the photovoltage across grains and grain boundaries, which is direct evidence of the inherently benign nature of microstructures, and the final device performance. This research elucidates underlying space‐resolved photoresponse mechanisms behind the lower efficiency of quasi‐2D RP perovskites compared with the 3D perovskites, which is necessary for further development of efficient and stable 2D perovskite‐based devices.

Oxide Ion Conduction, Defect Chemistry, and the Conducting Mechanism in Ruddlesden–Popper La2–xMxBaIn2O7–0.5x (M = Ca, Sr, Ba)

Tetragonal La2BaIn2O7 belongs to the stoichiometric n = 2 members of the Ruddlesden–Popper (RP) structure, with La3+ and Ba2+ cations ordered in the rock salt and octahedral layers, respectively. Herein, a series of alkaline-earth-metal-doped materials La2–xMxBaIn2O7–0.5x (M = Ca, Sr, Ba) were prepared by the traditional solid-state reaction method. The results revealed that the substitutions of Ca/Sr/Ba for La introduced oxygen vacancies and led to good oxide ion conduction, e.g., ∼1.21 × 10–3–1.38 × 10–2 S/cm within 600–900 °C for the specimen La1.7Ba1.3In2O6.85, which was more than 2 orders of magnitude higher than the parent material. However, both the parent and acceptor-doped La2BaIn2O7 showed very limited proton conductions. The energetics of defect formation and oxygen vacancy migrations in La2BaIn2O7-based materials was studied through the static lattice and molecular dynamics (MD) atomistic simulations based on the interatomic potential approach. The defect formation energy calculations for the electrons and holes in La2BaIn2O7 rationalized the experimentally observed pure ionic conduction under low pO2 and mixed ionic and p-type electronic conductions under high pO2, respectively. The MD simulations indicated two-dimensional oxygen vacancy migration within the perovskite slab for the acceptor-doped La2BaIn2O7.

2D Ruddlesden-Popper perovskite ferroelectric film for high-performance, self-powered and ultra-stable UV photodetector boosted by ferro-pyro-phototronic effect and surface passivation

2D Ruddlesden-Popper (RP) perovskites have attracted enormous attention in optoelectronic fields compared with their 3D counterparts. However, most of the reported perovskite ferroelectrics-based self-powered photodetectors (PDs) are fabricated from bulk single crystals rather than perovskite thin films with improved reproducibility, flexibility, and less preparation time. Nevertheless, the defect sites at surfaces and grain boundaries of 2D perovskites polycrystalline films make them vulnerable to humidity. Herein, the highly crystallized 2D RP perovskite ferroelectric films are successfully obtained. Then, a passivation method is applied on 2D perovskite film by an in-situ reaction with 4-fluoro-phenylethylamine iodide (4-FPEAI), which reduces the defect sites and endows the perovskite films with the outstanding hydrophobic property. Then, the as-prepared 2D-perovskite ferroelectric thin films were fabricated into self-powered PDs. Boosted by the ferro-pyro-phototronic effect, the self-powered PDs demonstrate excellent optoelectronic performances at 360 nm, with dark current less than 1 × 10−12 A, a peak responsivity over 1 A W−1, a detectivity of 1.5 × 1014 Jones and fast response/recovery speed. The photoresponsivity and specific detectivity are both enhanced by 67.8 times regarding the relative peak-to-peak current, compared with those only based on the photovoltaic induced photocurrent. Further, the PDs show high stability towards high humidity and thermal treatment.

Exploring the Steric Hindrance of Alkylammonium Cations in the Structural Reconfiguration of Quasi‐2D Perovskite Materials Using a High‐throughput Experimental Platform

AbstractReduced‐dimensional (2D or quasi‐2D) perovskites have recently attracted considerable interest due to their superior long‐term stability. The nature of the intercalating cations plays a key role in determining the physicochemical properties and stability of the quasi‐2D perovskites. Here, the thermal stability of a series of 2D Ruddlesden−Popper (RP) perovskites is studied using seven types of intercalating cations with increasing linear carbon‐chain length from ethylammonium (EA) to n‐dodecylammonium (DA) through a high‐throughput platform. The results show that long‐chain cations in quasi‐2D perovskite films lead to strong steric hindrance between adjacent perovskite domains, thus suppressing Ostwald ripening during the thermal‐aging process. For short‐chain cations, increased‐dimensional phase redistribution during the aging period is observed, which can benefit a concomitant regeneration of the 3D/3D‐like perovskite phases. The impact of steric hindrance on structural reconfiguration and the subsequent phase redistribution in quasi‐2D perovskites are systematically characterized by UV–vis absorption spectra, photoluminescence spectra, and X‐ray diffraction patterns. Due to the steric hindrance effect, an optimal chain length is found to maximize film stability by balancing the water/oxygen resistance and increased‐dimensional phase redistribution. This study provides new insight into the thermal stability of quasi‐2D perovskites.

Theoretical investigation of octahedral tilting and bandgap non‐linearity in monolayer Ruddlesden‐Popper A 2 Pb 1‐x Ge x I 4 perovskites

2D Ruddlesden-Popper (RP) perovskites (R-NH3)2An−1BnX3n+1 with tailorable photovoltaic features of low toxicity, reduced dimensionality, and defect tolerance hold promise to overcome the main constraints of perovskite solar cells (PSCs). A systematic investigation of the structural and electronic properties of pure and mixed (R-NH3)2Pb1−xGexI4 systems was performed with and without spin-orbit coupling (SOC), by using density functional theory (DFT). The organic spacer cations (R-NH3+)2 of methylammonium (MA-CH3NH3+) and Phenylethyl ammonium (PEA-C6H5[CH2]2NH3+) with x = 0.0, 0.25, 0.50, 0.75, 1.0, resulted in the compositionally modified 32-permutations by systematically substituting the inorganic cations. Short-range ordering has categorized all studied compositions of (R-NH3)2Pb0.50Ge0.50I4 into column and battenberg schemes depending on the Ge defect site. The competing effects of octahedral tilting and lattice distortion with bandgap bowing and SOC, across Pb-Ge compositional systems, provide a systematic strategy to tune bandgaps. By controlling the cations' composition, these mixed 2D-perovskites outlined the strategy to achieve the desired bandgap and band positions. A rational design approach of low dimensional perovskites was adopted to tune the electronic properties through the spacer and inorganic cation engineering. Our findings expose the scope of monolayer-based systems as an ideal choice of absorber for the bottom sub-cell in all-perovskites 2D-3D tandem solar cell, harvesting light from visible (2.4 eV) up to infrared (1.2 eV) in the solar spectrum with features of defect tolerance, quantum and dielectric confinement, low bandgap, low effective masses, and high mobility.

Enhanced efficiency and stability of Dion–Jacobson quasi-two-dimensional perovskite solar cells by additive

Dion–Jacobson (DJ) quasi-two-dimensional (quasi-2D) perovskite solar cells (PSCs) have attracted increasing attention owing to their potential stability compared with the Ruddlesden-Popper (RP) phase. It is known that the low efficiency and poor thermal stability retard the application of quasi-2D PSCs. Here, DJ quasi-2D perovskite films based on propane-1.3-diammonium (PDA) spacer cations were prepared by a hot casting technique. Ionic liquid additive of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) was introduced into the quasi-2D perovskite precursor solution to improve the crystal quality and morphology of the films. The quasi-2D PSCs with BMIMBF4 achieved an optimal power conversion efficiency (PCE) of 14.07%, which is higher than the 12.45% of the control devices. The impressive 1.17 V high open-circuit voltage and 14.07% efficiency are the highest values for the reported PDA-based n–i–p type devices. Moreover, the thermal stability of the solar cells was significantly enhanced by the addition of BMIMBF4. The PCE of the devices with BMIMBF4 maintains 72% of the initial value after annealing at 85 °C for 120 h, while the PCE of control devices drops to 19% of the initial value. These results prove that the introduction of ionic liquid BMIMBF4 is a pragmatic method to elevate the efficiency and thermal stability of quasi-2D PSCs.

Influence of Cr substitution on structural, optical, and magnetic properties of La2SrFe2O7: Their application as a photocatalyst for the degradation of Rhodamine B dye

A new n = 2 Ruddlesden-Popper (RP) series La2SrFe2-xCrxO7 (x = 0.0, 0.2, 0.4, 0.6 and 0.8) has been prepared via Sol-gel Pechini method, and their structural, optical, and the magnetic characterization was done. Furthermore, we are for the first-time reporting on the photo-catalytic degradation of a dye by a complete n = 2, La2SrFe2-xCrxO7 RP series. Rietveld refinement analysis confirms the formation of single-phase compounds with tetragonal crystal symmetry and I4/mmm space group. The results indicate a steady decrease in unit cell parameters and cell volume with Cr3+ doping. Dominant anti-ferromagnetic (AFM) interactions were observed in all the phases and the appearance of weak ferromagnetic (FM) interactions takes place owing to the Fe3+―O―Cr3+ FM interaction with Cr3+ doping. The χM−FC curve for x = 0.8 phase shows the magnetization reversal (MR) phenomenon and becomes zero at Tcomp ∼127 K and the value becomes negative on further decreasing the temperature. The MR phenomenon is discussed in terms of the competing Fe3+―O―Fe3+, Fe3+―O―Cr3+, and Cr3+―O―Cr3+ super-exchange interactions. Enhanced photocatalytic activity for the degradation of Rhodamine B (RhB) dye was obtained for x = 0.2 substituted phase, displaying a ∼99% degradation of dye in 30 min followed by ∼83%, ∼75%, ∼64% and ∼61% by x = 0.4, 0.0, 0.8 and 0.6 phases respectively in the same time interval. The results are explained in terms of crystallite size, the narrowing of band gap with Cr3+ substitution, and based on of recombination of charge carriers which, are in good agreement with the results of Photoluminescence (PL) emission intensity spectra.