Defect Perovskite Research Articles

Enhanced oxygen evolution on A-site defect perovskite oxide through interfacial engineering

Perovskite oxides are emerging as promising alternative to precious metal-based electrocatalysts for oxygen evolution reactions. Despite their potential, their catalytic activity is often insufficient for practical applications. In this study, we demonstrate that introducing A-site defects in LaNiO3 perovskite oxides promotes B-site exsolution during the reduction process. Subsequent chemical vapor deposition introduces selenium, forming an electrocatalyst with a heterojunction structure. Comprehensive characterization and electrochemical testing reveal that the r-La0.9NiO3/NiSex heterojunction structure, resulting from B-site exsolution induced by A-site defects, significantly enhances the electrocatalytic performance of the La0.9NiO3 electrocatalyst. This novel structure not only increases oxygen vacancy concentration but also improves the wettability of the electrocatalyst, as indicated by a reduced bubble contact angle in water. These modifications lead to a notable improvement in the electrochemical performance of the r-La0.9NiO3/NiSex electrocatalyst. At a current density of 10 mA·cm−2, the electrocatalyst exhibits an overpotential of 297.6 mV, with substantially increased mass activity. This study presents a novel approach to catalyst design in electrocatalysis, leveraging A-site defect induced B-site exsolution in perovskite oxides. The strategy of reduction followed by doping offers a robust framework for developing more efficient electrocatalysts, paving the way for advancements in the field of heterogeneous catalysis.

DFT study of optoelectronic and thermoelectric properties of pure and doped double perovskite Cs2SnI6 for solar cell applications

The global need of energy is raising day by day. To meet this demand double perovskites (DPs) can play a vital role for energy conversion devices. In this letter, we formulated and examined lead-free defect perovskites using a combination of tellurium and tin, denoted as Cs2Sn1-xTexI6 (0, 0.25), utilizing density functional theory which include structural, optical and thermal behavior. Both the optimized volume and lattice parameter exhibit a linear increase with the Te content in Cs2Sn1-xTexI6 (CsSnTeI). The negative value of formation energy for both pure and doped materials along with their Poisson and Pugh ratio confirm the stability of these materials. The band structure analysis reveals its semiconducting behavior, with the band gap expanding proportionally to the increased Te concentration with band gap value of pure (1.20 eV) and doped 91.43 eV) double perovskites. Optical characteristics, including the dielectric function and absorption coefficient, were also analyzed. To expose their potential use of Cs2Sn1-xTexI6 (0, 0.25) in thermoelectric devices, temperature dependent thermoelectric features are investigated reveal that suitability of these materials for energy conversion purposes.

Development of Lead‐Free Defect Brownmillerite Perovskite Ceramic LiBiFeMnO5 Solid Solution for Electronic Devices

This article reports the fabrication (synthesis) and characterizations (structural, microstructural topographic surface, dielectric, transport, impedance, current–voltage, and resistive properties) of a complex lead‐free defect perovskite material of composition LiBiFeMnO5. A preliminary structural investigation of the X‐ray diffraction pattern using N‐TREOR09 methods shows monoclinic symmetry. The scanning electron microscopic spectrum examines the sample's microstructural topographic surface, fractal study, and roughness (using the standard ISO25178). The analysis of Maxwell–Wagner dielectric dispersion, relaxation, and transport mechanisms is investigated utilizing dielectric, impedance, and conductivity spectrum accumulated within the experimental frequency of (1 kHz–1 MHz) at different temperatures (30–500 °C). A nonoverlapping small polaron tunneling conduction mechanism and correlated barrier hopping mechanism in the material have helped to understand its conduction phenomena. The Ohmic and space–charge limited conduction mechanisms are investigated by the slope of the logarithmic electric field (E) and current density (J). The thermistor constant (β) is determined to be 1982.87. The temperature coefficient of resistance is found to be −0.00419, which may be suitable for negative temperature coefficient thermistors, sensors, and other related devices.

Accelerated peroxymonosulfate activation over defective perovskite with anchored cobalt nanoparticles for organic contaminant removal

In this study, a novel perovskite oxide (Co@D-PBSC) for activation peroxymonosulfate (PMS) to degrade organic pollutants in wastewater was developed. Cobalt nanoparticles (Co NPs) and oxygen vacancies (OVs) were introduced to the perovskite oxide lattice via a non-stoichiometric ratio and separate-out strategy. The OVs and Co NPs provided abundant active sites for the activation of PMS and the generation of reactive oxygen species. The Co metal-OVs bridge promote the adsorption of PMS, meanwhile, Co nanoparticles accelerate the Co2+/Co3+ redox cycle, resulting in the production of the main reactive substance, sulfate radicals (SO4•−). The results of catalytic experiments showed that 85 % of ofloxacin (OFX) degradation efficiency was obtained within 1 min at 0.1 g/L Co@D-PBSC, 0.3 g/L PMS, 20 mg/L OFX (150 mL), and solution pH 7.0, which indicated that Co@D-PBSC/PMS system exhibits excellent performance. This work demonstrated an efficient perovskite catalyst for PMS activation in wastewater treatment and provided a useful catalyst design strategy for the advanced oxidation processes (AOPs).

Synthesis and Properties of the Helium Clathrate and Defect Perovskite [He2-x □ x ][CaNb]F6.

The defect double perovskite [He2-x □ x ][CaNb]F6, with helium on its A-site, can be prepared by the insertion of helium into ReO3-type CaNbF6 at high pressure. Upon cooling from 300 to 100 K under 0.4 GPa helium, ∼60% of the A-sites become occupied. Helium uptake was quantified by both neutron powder diffraction and gas insertion and release measurements. After the conversion of gauge pressure to fugacity, the uptake of helium by CaNbF6 can be described by a Langmuir isotherm. The enthalpy of absorption for helium in [He2-x □ x ][CaNb]F6 is estimated to be ∼+3(1) kJ mol-1, implying that its formation is entropically favored. Helium is able to diffuse through the material on a time scale of minutes at temperatures down to ∼150 K but is trapped at 100 K and below. The insertion of helium into CaNbF6 reduces the magnitude of its negative thermal expansion, increases the bulk modulus, and modifies its phase behavior. On compressing pristine CaNbF6, at 50 and 100 K, a cubic (Fm3̅m) to rhombohedral (R3̅) phase transition was observed at <0.20 GPa. However, a helium-containing sample remained cubic at 0.4 GPa and 50 K. CaNbF6, compressed in helium at room temperature, remained cubic to >3.7 GPa, the limit of our X-ray diffraction measurements, in contrast to prior reports that upon compression in a nonpenetrating medium, a phase transition is detected at ∼0.4 GPa.

Superior performance of rubidium/acetate co-doped CsPbIBr2 perovskite solar cells: A comprehensive analysis

The development of remarkably resourceful, effectively phase stable, and highly crystalline-minimal defect perovskite (PVT)-based solar cells (PSCs) is extremely needful for the existing energy requisites. The strategy of incorporating appropriate dopants such as metal cations/anions into inorganic PVT lattices has been recognized as a successful methodology to attain aforesaid PSCs. On that account, this analysis reveals the implication of rubidium (Rb)/ acetate (Ac) (cation/anion) co-doping upon cesium (Cs)-based, bromine (Br)-rich PVT: CsPbIBr2 against undoped equivalent. The thorough numerical study on recommended structure: FTO/SnO2/CsPbIBr2/CuAlO2/Ag specifying recombination profiles and performance parameters with respect to layer parameters of PVT absorber and charge transport layers conveyed supreme behavior from co-doped devices. It is evidenced that highest efficiency of 16.79 % is accomplished from Rb/Ac co-doped PSC for PVT electron mobility of 25 cm2V-1s−1. The work reveals the progress in photovoltaic characteristics of inorganic PSCs through the involvement of multi-source co-doping.

Numerical simulation based performance enhancement approach for an inorganic BaZrS3/CuO heterojunction solar cell

One of the main components of the worldwide transition to sustainable energy is solar cells, usually referred to as photovoltaics. By converting sunlight into power, they lessen their reliance on fossil fuels and the release of greenhouse gases. Because solar cells are decentralized, distributed energy systems may be developed, which increases the efficiency of the cells. Chalcogenide perovskites have drawn interest due to their potential in solar energy conversion since they provide distinctive optoelectronic characteristics and stability. But high temperatures and lengthy reaction periods make it difficult to synthesise and process them. Therefore, we present the inaugural numerical simulation using SCAPS-1D for emerging inorganic BaZrS3/CuO heterojunction solar cells. This study delves into the behaviour of diverse parameters in photovoltaic devices, encompassing efficiency (η) values, short-circuit current density (Jsc), fill factor (FF), and open-circuit voltage (Voc). Additionally, we thoroughly examine the impact of window and absorber layer thickness, carrier concentration, and bandgap on the fundamental characteristics of solar cells. Our findings showcase the attainment of the highest efficiency (η) values, reaching 27.3% for our modelled devices, accompanied by Jsc values of 40.5 mA/cm2, Voc value of 0.79 V, and FF value of 85.2. The efficiency (η) values are chiefly influenced by the combined effects of Voc, Jsc, and FF values. This optimal efficiency was achieved with CuO thickness, band gap, and carrier concentration set at 5 µm, 1.05 eV, and above 1019 cm−3, respectively. In comparison, the optimal parameters for BaZrS3 include a thickness of 1 µm, a carrier concentration below 1020 cm−3, and a band gap less than 1.6 eV. Therefore, in the near future, the present simulation will simultaneously provide up an entirely novel field for the less defective perovskite solar cell.

Gamma-ray dose threshold for MAPbI3 solar cells.

In this work, we report on the effects observed in MAPbI3 polycrystalline films and solar cells under moderate gamma-ray doses of 3-21 kGy. We applied several instrumental techniques such as photoluminescence spectroscopy, time-resolved photoluminescence, Suns-VOC measurement, and impedance spectroscopy to characterize exposed samples. We observed a nonlinear dependency of such characteristics as PL intensity, career lifetime, ideality factor, and recombination resistance on the exposure dose. Small doses of 3-5 kGy annihilate some of the defect centers in the material, which results in improved carrier extraction and prolonged carrier lifetime, while with larger doses of 10 kGy and above, nonradiative recombination becomes predominant. In this way, we revealed a gamma-ray threshold for MAPbI3 films of around 10 kGy, above which it is not recommended to exploit this material. In space environment, yearly doses rarely exhibit 0.1 kGy (10 krad), and the MAPbI3 material has a sufficient margin of safety for space applications. Moreover, this unusual behaviour opens up the opportunity to use gamma-ray sources as an effective method to improve the quality of defective polycrystalline perovskite films before actual exploitation in an ionizing radiation-free environment.

Retarding Ion Migration for Stable Blade-Coated Inverted Perovskite Solar Cells.

The fabrication of perovskite solar cells (PSCs) through blade coating is seen as one of the most viable paths toward commercialization. However, relative to the less scalable spin coating method, the blade coating process often results in more defective perovskite films with lower grain uniformity. Ion migration, facilitated by those elevated defect levels, is one of the main triggers of phase segregation and device instability. Here, a bifunctional molecule, p-aminobenzoic acid (PABA), which enhances the barrier to ion migration, induces grain growth along the (100) facet, and promotes the formation of homogeneous perovskite films with fewer defects, is reported. As a result, PSCs with PABA achieved impressive power conversion efficiencies (PCEs) of 23.32% and 22.23% for devices with active areas of 0.1 cm2 and 1 cm2 , respectively. Furthermore, these devices maintain 93.8% of their initial efficiencies after 1000 h under 1-sun illumination, 75 °C, and 10% relative humidity conditions.

A defective iron-based perovskite cathode for high-performance IT-SOFCs: Tailoring the oxygen vacancies using Nb/Ta co-doping

The sluggish kinetics of the electrochemical oxygen reduction reaction (ORR) in intermediate-temperature solid oxide fuel cells (IT-SOFCs) greatly limits the overall cell performance. In this study, an efficient and durable cathode material for IT-SOFCs is designed based on density functional theory (DFT) calculations by co-doping with Nb and Ta the B-site of the SrFeO3−δ perovskite oxide. The DFT calculations suggest that Nb/Ta co-doping can regulate the energy band of the parent SrFeO3−δ and help electron transfer. In symmetrical cells, such cathode with a SrFe0.8Nb0.1Ta0.1O3−δ (SFNT) detailed formula achieves a low cathode polarization resistance of 0.147 Ω cm2 at 650 °C. Electron spin resonance (ESR) and X-ray photoelectron spectroscopy (XPS) analysis confirm that the co-doping of Nb/Ta in SrFeO3−δ B-site increases the balanced concentration of oxygen vacancies, enhancing the electrochemical performance when compared to 20 mol% Nb single-doped perovskite oxide. The cathode button cell with Ni-SDC|SDC|SFNT configuration achieves an outstanding peak power density of 1.3 W cm−2 at 650 °C. Moreover, the button cell shows durability for 110 h under 0.65 V at 600 °C using wet H2 as fuel.

Porous Lead Iodide Layer Promotes Organic Amine Salt Diffusion to Achieve High Performance p‐i‐n Flexible Perovskite Solar Cells

AbstractFlexible perovskite solar cells (FPSCs) are attracting widespread research and attention for their benefits as the next‐generation wearable electronic products. However, there are still many challenges in the quest to achieve dense, pinhole‐free, high crystal quality, low defect, and stable perovskite films, which limit further improvement in the efficiency and stability of FPSCs. Herein, a novel technique for the incorporation of quaternary ammonium halide (QAH) additives to prepare fluffy porous lead iodide layers by using a two‐step sequential deposition method, is reported. Benefiting from the good diffusion of organic amine salts on porous PbI2 layers, flat and dense perovskite films are produced with large particle sizes, few defects, and high crystal quality. Finally, the champion rigid and flexible p‐i‐n PSCs with the 2‐(acetyloxy)‐N,N,N‐trimethylethanium chloride (AtaCl) additive achieves exciting power conversion efficiencies (PCE) of 23.40% and 21.10%, respectively. The device with the AtaCl additive retains over 90% of its original PCE under ambient conditions (40 ± 5% relative humidity (RH)) over 1000 h of aging without encapsulation. In addition, the flexible device with the AtaCl additive shows excellent stability under mechanical bending conditions, retaining ≈85% of its original PCE after 10 000 cycles (bending radius = 5 mm).

Ab initio calculations of the properties of defective CsSnCl3: The role of anion-cation pair defect

In this study, first principles calculations based on density functional theory (DFT) was used to simulate the geometric structures, electronic, optical, and mechanical properties, of inorganic CsSnCl3 perovskites with and without an anion-cation pair defect (Sn and Cl vacancy). The data establishes that the introduction of vacancies induce a trap state which narrows the band gap. The formation of the observed trap states can be ascribed to the orbital hybridization of the Sn atoms near the vacancy site. In addition, the defective CsSnCl3 perovskite showed better light absorption in the visible region than its pristine counterpart owing to a reduced band gap. The mechanical properties predicted the pristine and defective CsSnCl3 perovskites to be mechanically stable.

Lead-free defective halide perovskites Cs2SnX6 (X = Cl, Br, I) for highly robust formaldehyde sensing at room temperature

In this contribution, all-inorganic lead-free halide perovskites Cs2SnX6 (X = Cl, Br, I) were synthesized by simple room-temperature precipitation. Material characterization demonstrated their feature in rich defects of halogen vacancies. As room-temperature formaldehyde (HCHO) sensing materials, Cs2SnX6 exhibited reliable sensitivity order of Cs2SnCl6 < Cs2SnBr6 < Cs2SnI6. Notably, the Cs2SnI6 sensor showed excellent selectivity for HCHO at room temperature with high response (Sr = 78, 100 ppm), short response/recovery time (3.6 s/7.2 s), good repeatability and long-term stability. Finally, the HCHO sensing mechanism was investigated via in-situ infrared analysis, conforming abundant intermediates of dioxymethylene, formate, and carbonate. The excellent sensing performance is attributed to rich iodine vacancies (VI) as active sites induced boosted stepwise oxidation of HCHO molecules on Cs2SnI6 surface. This work provides a fine candidate for practical HCHO detection at room temperature, and furthermore, gives new insights in designing halide perovskites for next-generation sensory devices.

Foldable Hole-Transporting Materials for Merging Electronic States between Defective and Perfect Perovskite Sites.

Defective and perfect sites naturally exist within electronic semiconductors, and considerable efforts to reduce defects to improve the performance of electronic devices, especially in hybrid organic-inorganic perovskites (ABX3 ), are undertaken. Herein, foldable hole-transporting materials (HTMs) are developed, and they extend the wavefunctions of A-site cations of perovskite, which, as hybridized electronic states, link the trap states (defective site) and valence band edge (perfect site) between the naturally defective and perfect sites of the perovskite surface, finally converting the discrete trap states of the perovskite as the continuous valence band to reduce trap recombination. Tailoring the foldability of the HTMs tunes the wavefunctions between defective and perfect surface sites, allowing the power conversion efficiency of a small cell to reach 23.22% and that of a mini-module (6.5 × 7cm, active area=30.24cm2 ) to reach as high as 21.71% with a fill factor of 81%, the highest value reported for non-spiro-OMeTAD-based perovskite solar modules.

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.

Atomic-scale origin of the low grain-boundary resistance in perovskite solid electrolyte Li0.375Sr0.4375Ta0.75Zr0.25O3

Oxide solid electrolytes (OSEs) have the potential to achieve improved safety and energy density for lithium-ion batteries, but their high grain-boundary (GB) resistance generally is a bottleneck. In the well-studied perovskite oxide solid electrolyte, Li3xLa2/3-xTiO3 (LLTO), the ionic conductivity of grain boundaries is about three orders of magnitude lower than that of the bulk. In contrast, the related Li0.375Sr0.4375Ta0.75Zr0.25O3 (LSTZ0.75) perovskite exhibits low grain boundary resistance for reasons yet unknown. Here, we use aberration-corrected scanning transmission electron microscopy and spectroscopy, along with an active learning moment tensor potential, to reveal the atomic scale structure and composition of LSTZ0.75 grain boundaries. Vibrational electron energy loss spectroscopy is applied for the first time to reveal atomically resolved vibrations at grain boundaries of LSTZ0.75 and to characterize the otherwise unmeasurable Li distribution therein. We find that Li depletion, which is a major reason for the low grain boundary ionic conductivity of LLTO, is absent for the grain boundaries of LSTZ0.75. Instead, the low grain boundary resistivity of LSTZ0.75 is attributed to the formation of a nanoscale defective cubic perovskite interfacial structure that contained abundant vacancies. Our study provides new insights into the atomic scale mechanisms of low grain boundary resistivity.

Atomic Model for Alkali Metal-Doped Tin–Lead Mixed Perovskites: Insight from Quantum Dynamics

Defects such as metal vacancies act as nonradiative recombination centers to deteriorate the photoelectric properties of metal halide perovskites. Nonadiabatic molecular dynamics has demonstrated that alkali metal dopants markedly improve the performance of mixed tin-lead perovskites. Alkali dopants increase the formation energy of tin vacancies to 1 eV, so that the defect concentration is decreased. When tin vacancies exist, alkali metals are easily doped into perovskites. Tin vacancies produce iodine trimers that create midgap states and cause rapid electron-hole recombination. Alkali metal additives eliminate the trap state, weaken nonadiabatic coupling, and decelerate charge recombination with a coefficient of ≤5.5 compared with the performance of the defective tin-lead mixed perovskite. Our research has constructed a theoretical model at the atomic level for alkali metal passivation that enhances defect tolerance of tin-lead mixed perovskites, generating valuable inspiration for optimizing high-performance perovskites.

High quality quasi-two-dimensional organic–inorganic hybrid halide perovskite film for high performance photodetector

Two-dimensional (2D) Ruddlesden–Popper perovskites have attracted extensive attention in photodetectors (PDs) due to their exceptional optoelectronic properties. The performances of PDs show extremely strong dependence on defects in 2D perovskites. Herein, high quality and less defective BA2FAPb2I7 perovskite films were obtained by a simple one-step spin coating method with rare earth doping assisted crystal growth. Furthermore, BA2FAPb2I7 perovskite films were used as photoresponsive materials to fabricate architectural simplicity photoconductor PDs. Under 405 nm laser illumination, the PDs show remarkable balance detect properties with a low dark current of 5.1 × 10−11 A, a large on/off ratio of 2.2 × 105, a high responsivity (R) of 4.51 A/W, an outstanding detectivity Dshot* of 4.31 × 1013 Jones, and a response speed of 80 μs/76 μs. The R and Dshot* of the PDs are outstanding in the reported quasi-2D perovskite PDs with the same structure. Our work not only paves an indubitably feasible way for fabrication of quasi-2D perovskite PDs via improving their natural material properties but also provides a clear direction for further enhancing the performance of other perovskites optoelectronics.

Importance of Low Humidity and Selection of Halide Ions of Octylammonium Halide in 2D–3D Perovskite Solar Cells Fabricated in Air

AbstractAir fabrication of efficient and stable perovskite solar cells with substantial reproducibility is of importance for commercialization of perovskite solar cells. There has been little consensus on which halide is the best selection for thin 2D perovskite layer on 3D perovskite when processing in ambient air. In this work, the influence of humidity and halide ions in alkylammonium halide (OAX)‐treated perovskite layer on photovoltaic performance is investigated. The authors find that a combination of high humidity and the presence of chloride ions can induce the deprotonation of methylammonium (MA+) ions. With X‐ray diffraction, cross‐sectional scanning electron microscope, Fourier‐transform infrared spectroscopy, the authors elucidate that the deprotonation reaction in the octylammonium chloride (OACl)‐treated perovskite layer makes MA+ ions (CH3NH3+) volatile MA (CH3NH2), which results in void volumes and defects in the bulk of perovskite layer as well as at the interface. The defective perovskite solar cells induced by the deprotonation reaction have the suppressed hole transfer at the interface between the perovskite layer and the hole transport layer, yielding the reduced internal quantum efficiency and JSC. Space charge‐limited current analysis reveals that the reduced VOC is caused by the high trap density estimated from VTFL of hole‐only devices.

Band gap tuning through cation and halide alloying in mechanochemically synthesized Cs3(Sb1−xBix)2Br9 and Cs3Sb2(I1−xBrx)9 solid solutions

Modulation of the optical properties of lead-free defective perovskites can contribute to the design of optimized materials for several applications ranging from photodetection to photocatalysis.