Ion migration in halide perovskite solar cells:Mechanism,characterization,impact and suppression

Metal halide perovskites are emerging as the most promising candidate for the next-generation Photovoltaics(PV)materials,due to their superior optoelectronic properties and low cost.However,the resulting Perovskite solar cells(PSCs)suffer from poor stability.In particular,the temperature and light activated ionic defects within the perovskite lattice,as well as electric-field-induced migration of ionic defects,make the PSCs unstable at operating condition,even with device encapsulation.There is no doubt that the investigation of ion migration is crucial for the development of PSCs with high intrinsic stability.In this review,we first briefly introduce the origin and pathways of ion migration,and also the essential characterization methods to identify ion migration.Next,we discuss the impact of ion migration on the perovskite films and cells with respect to photoelectric properties and stability.Then,several representative strategies to suppress ion migration are systematically summarized in the context of composition engineering,additive engineering and interface engineering,with an in-depth understanding on the underlying mechanisms which may provide more clues for further fabrication of PSCs with improved stability.Finally,a perspective with some suggestion on future research directions and chemical approaches are provided to alleviate ion migration in perovskite materials and the entire devices.

Migration and distribution of saline ions in bauxite residue during water leaching

Bauxite residue,a highly saline solid waste produced from digestion of bauxite for alumina production,is hazardous to the environment and restricts vegetation establishment in bauxite residue disposal areas.A novel water leaching process proposed here was used to investigate the dynamic migration and vertical distribution of saline ions in bauxite residue.The results show that water leaching significantly reduced the salinity of bauxite residue,leaching both saline cations Na+,K+,Ca2+and anions CO32-,SO42-,HCO3-.Na+and K+migrated from 40-50 to 20-30 cm of the column,presenting a high migration capacity.The migration capacity of Ca2+was lower and accumulated at 30-40 cm of the column.CO32-initially distributed at 20-30 cm of the column,subsequently transported to 30-40 cm of the column,and finally returned to 20-30 cm of the column along with evaporation.SO42-was originally distributed at 40-50 cm,but finally migrated to 20-30 cm of the column.Nevertheless,HCO3-remained at the bottom of the column,and its migratory was less affected by evaporation.

Suppression of ion migration in perovskite materials by pulse-voltage method

Hybrid halide perovskites have great potential for applications in optoelectronic devices.However,the typical ion migration in perovskite could lead to the non-repeatability of electrical measurement,instability of material,and degradation of device performance.The basic current–voltage behavior of perovskite materials is intricate due to the mixed electronic–ionic characteristic,which is still poorly understood in these semiconductors.Developing novel measurement schematic is a promising solution to obtain the intrinsic electrical performance without the interference of ion migration.Herein,we explore the pulse-voltage(PV)method on methylammonium lead tribromide single crystals to protect the device from the ion migration.A guideline is summarized through the analysis of measurement history and condition parameters.The influence of the ion migration on current–voltage measurement,such as repeatability and hysteresis loop,is under controlled.An application of the PV method is demonstrated on the activation energy of conductivity.The abruption of activation energy still exists near the phase transition temperature despite the ion migration is excluded by the PV method,introducing new physical insight on the current–voltage behavior of perovskite materials.The guideline on PV method will be beneficial for measuring halide perovskite materials and developing optoelectronic applications with new technique schematic.

Ion migration in metal halide perovskite QLEDs and its inhibition

Benefiting from the excellent properties such as high photoluminescence quantum yield(PLQY), wide gamut range,and narrow emission linewidth, as well as low-temperature processability, metal halide perovskite quantum dots(QDs)have attracted wide attention from researchers. Despite tremendous progress has been made during the past several years,the commercialization of perovskite QDs-based LEDs(PeQLEDs) is still plagued by the instability. The ion migration in halide perovskites is recognized as the key factor causing the performance degradation of PeQLEDs. In this review, the elements species of ion migration, the effects of ion migration on device performance and stability, and effective strategies to hinder/mitigate ion migration in PeQLEDs are successively discussed. Finally, the forward insights on the future research are highlighted.

Crucial role of charge transporting layers on ion migration in perovskite solar cells

The device preconditioning dependent hysteresis and the consequential performance degradation hinder the actual performance and stability of the perovskite solar cells. Ion migration and charge trapping in the perovskite with large contribution from grain boundaries are the most common interpretations for the hysteresis. Yet, the high performing devices often include intermediate hole and electron transporting layers, which can further complicate the dynamical process in the device. Here, by using Kelvin Probe Force Microscopy and Confocal Photoluminescence Microscopy, we elucidate the impact of chargetransporting layers and excess MAI on the spatial and temporal variations of the photovoltage on the MAPbI3-based solar cells. By studying the devices layer by layer, we found that the light-induced ion migration occurs predominantly in the presence of an imbalanced charge extraction in the solar cells, and the charge transporting layers play crucial role in suppressing it. Careful selection and processing of the electron and hole-transporting materials are thus essential for making perovskite solar cells free from the ion migration effect.

In situ Investigations of Interfacial Degradation and Ion Migration at CH3NH3PbI3 Perovskite/Ag Interfaces

Interfacial properties between perovskite layers and metal electrodes play a crucial role in the device performance and the long-term stability of perovskite solar cells.Here,we report a comprehensive study of the interfacial degradation and ion migration at the interface between CH3NH3PbI3 perovskite layer and Ag electrode.Using in situ photoemission spectroscopy measurements,we found that the Ag electrode could induce the degradation of perovskite layers,leading to the formation of PbI2 and AgI species and the reduction of Pb^2+ions to metallic Pb species at the interface.The unconventional enhancement of the intensities of I 3d spectra provides direct experimental evidences for the migration of iodide ions from CH3NH3PbI3 subsurface to Ag electrode.Moreover,the contact of Ag electrode and perovskite layers induces an interfacial dipole of 0.3 eV at CH3NH3PbI3/Ag interfaces,which may further facilitate iodide ion diffusion,resulting in the decomposition of perovskite layers and the corrosion of Ag electrode.

Effects of Doping and Oxygen Vacancy Concentrations on Oxygen Ion Migration in SmxCe1-xO2-δ: a DFT + U Study

Influence of doping and oxygen vacancy concentrations on oxygen ion or oxygen vacancy（V） migration energies of SmxCe1-xO2-δ（x = 0.0625, 0.125, 0.25 and δ = 0.0625, 0.125） systems using a GGA+U method are studied. Calculated results show that advantage migration types change from V?O2- to O2- ?V as x and δ increase. For V?O2- migrations of the Sm0.0625Ce0.9375O1.9375 and Sm0.125Ce0.875O1.9375 systems, electrostatic attractions between Sm3+ and V, defect associations between Ce3+ and V, and steric hindrances of Sm3+ affect the migration energies. For O2- ?V migrations of the Sm+（0.125）Ce0.875O1.875 and Sm0.25Ce0.75O1.875 systems, migration energies of O2- are affected by electrostatic repulsions between Sm3+ and O2- and defect associations between Ce3+ and V. Increases of the oxygen vacancy and Sm3+ doping concentrations benefit the oxygen ion and vacancy migrations, respectively.

Migration process of ammonium ion in saturated silty sand and sandy loam

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Polypyride intercalation boosting the kinetics and stability of V_(3)O_(7)·H_(2)O cathodes for aqueous zinc-ion batteries

V_(3)O_(7)·H_(2)O(VO)is a high capacity cathode material in the field of aqueous zinc ion batteries(AZIBs),but it is limited by slow ion migration and low electrical conductivity.In this paper,polypyridine(PPyd)intercalated VO with nanoribbon structure was prepared by a simple in-situ pre-intercalation,which is noted VO-PPyd.The total density of states(TDOS)shows that after the pre-intercalation of PPyd,an intermediate energy level appears between the valence band and conduction band,which provides a step that can effectively reduce the band gap and enhance the electron conductivity.Furthermore,the density functional theory(DFT)results found that Zn^(2+)is more easily de-intercalated from the V-O skeleton,which proves that the embeddedness of PPyd improves the diffusion kinetics of Zn^(2+).Electrochemical studies have shown that VO-PPyd cathode materials exhibit excellent rate performance(high specific capacity of 465 and 192 mA h g^(-1)at 0.2 and 10 A g^(-1),respectively)and long-term cycling performance(92.7%capacity retention rate after 5300 cycles),due to their advantages in structure and composition.More importantly,the energy density of VO-PPyd//Zn at 581 and 5806 W kg^(-1)is 375 and 247 W h kg^(-1),respectively.VO-PPyd exhibits excellent electrochemical properties compared to previously reported vanadium based cathodes,which makes it highly competitive in the field of high-performance cathode materials of AZIBs.

Defect Engineering:Can it Mitigate Strong Coulomb Effect of Mg^(2+)in Cathode Materials for Rechargeable Magnesium Batteries?

Rechargeable magnesium batteries(RMBs)have been considered a promising“post lithium-ion battery”system to meet the rapidly increasing demand of the emerging electric vehicle and grid energy storage market.However,the sluggish diffusion kinetics of bivalent Mg^(2+)in the host material,related to the strong Coulomb effect between Mg^(2+)and host anion lattices,hinders their further development toward practical applications.Defect engineering,regarded as an effective strategy to break through the slow migration puzzle,has been validated in various cathode materials for RMBs.In this review,we first thoroughly understand the intrinsic mechanism of Mg^(2+)diffusion in cathode materials,from which the key factors affecting ion diffusion are further presented.Then,the positive effects of purposely introduced defects,including vacancy and doping,and the corresponding strategies for introducing various defects are discussed.The applications of defect engineering in cathode materials for RMBs with advanced electrochemical properties are also summarized.Finally,the existing challenges and future perspectives of defect engineering in cathode materials for the overall high-performance RMBs are described.

Two‑Dimensional Metal Halides for X‑Ray Detection Applications

Metal halide perovskites have recently emerged as promising candidates for the next generation of X-ray detectors due to their excellent optoelectronic properties.Especially,two-dimensional(2D)perovskites afford many distinct properties,including remarkable structural diversity,high generation energy,and balanced large exciton binding energy.With the advantages of 2D materials and perovskites,it successfully reduces the decomposition and phase transition of perovskite and effectively suppresses ion migration.Meanwhile,the existence of a high hydrophobic spacer can block water molecules,thus making 2D perovskite obtain excellent stability.All of these advantages have attracted much attention in the field of X-ray detection.This review introduces the classification of 2D halide perovskites,summarizes the synthesis technology and performance characteristics of 2D perovskite X-ray direct detector,and briefly discusses the application of 2D perovskite in scintillators.Finally,this review also emphasizes the key challenges faced by 2D perovskite X-ray detectors in practical application and presents our views on its future development.

Controlling Ion Conductance and Channels to Achieve Synapticlike Frequency Selectivity

Enhancing ion conductance and controlling transport pathway in organic electrolyte could be used to modulate ionic kinetics to handle signals. In a Pt/Poly(3-hexylthiophene-2,5-diyl)/Polyethylene?Li CF3SO3/Pt hetero-junction, the electrolyte layer handled at high temperature showed nano-fiber microstructures accompanied with greatly improved salt solubility. Ions with high mobility were confined in the nano-fibrous channels leading to the semiconducting polymer layer,which is favorable for modulating dynamic doping at the semiconducting polymer/electrolyte interface by pulse frequency.Such a device realized synaptic-like frequency selectivity, i.e., depression at low frequency stimulation but potentiation at high-frequency stimulation.

Layered buserite Mg-Mn oxide cathode for aqueous rechargeable Mg-ion battery

Owing to the features(high safety,inexpensive and environmental friendliness)of aqueous rechargeable Mg-ion batteries(ARMIBs),they have drawn extensive attention in the future energy storage systems.However,the poor Mg^(2+)migration kinetics during the Mg^(2+)intercalation/extraction still hinders the progress of developing suitable cathode materials.Herein,a layered buserite Mg-Mn oxide(MMO)material with large interlayer space(~9.70A)and low-crystalline structure is studied as a high-performance cathode in ARMIBs.Compared with the counterpart,the Mg^(2+)migration kinetics of the MMO cathode can be enhanced by its unique structure(bigger interlayer spacing and low-crystalline structure).The layered buserite MMO as a high-performance ARMIBs cathode exhibits high Mg storage capacity(50 mAg^(-1):169.3 mAh g^(-1)),excellent rate capability(1000 mAg^(-1):98.3 mAh g^(-1)),and fast Mg^(2+)migration(an average diffusion coefficient:~4.21×10-^(10)cm^(2)s^(-1))in 0.5 M MgCl_(2)aqueous electrolyte.Moreover,the MMO-1//AC full battery achieved a high discharge capacity(100 mAg^(-1):111 mAh g^(-1)),and an ignored fading over 5000 cycles(1000 mAg^(-1)).Therefore,layered Mg-Mn oxide with large interlayer space may break a new path to develop the promising ARMIBs.

Diagenetic Reactions in Reservoir Strata and Geochemical Properties of Pore Fluid and Its Origin in Songliao Basin

The reservoirs of the Songliao Basin are Composed of typical unstable sandstones,with high percentages of volcanic fragments and feldspar. In the course of sedimentation andburying, a series of physical and chemical reactions took place between minerals and pete waterand water-rock reactions and ion exchange caused changes in ion assemblage of pore water. Hydration-hydrolysis, dissolution and the albitization of feldspar made many ions free from theirframework and inter into the pore water, and induced the precipitation of a large amount of authigenic minerals such as smectite and chlorite. DUring the diagenesis of sandstone, diageneticreactions involved several stages with increasing depth, and so did the precipitation of authigenic minerals and the transformation of minerals. The migration of ions is related with theprecipitation, transformation and dissolution of authigenic minerals. Thus, to deepen our studyon sandstone diagenesis is an important link for the analysis of ion migration in the evolution ofpore water. The origin and evolution of Pore water could be tracked in terms of the geochemistry of fluid inclusions in authigenic minerals. And the isotopic composition of the authigenicmineral calcite can provide its genetic information.

Mixed low-dimensional metal halide perovskite singlecrystal for low-detection-limit x-ray detection via orientedion migration

Low-dimensional metal halide perovskites exhibit exceptional photoelectronicproperties and intrinsic stability, positioning them as a promising class of semiconductormaterials for light-emitting devices and photodetectors. In thiswork, we present a millimeter-scale single crystal of mixed low-dimensional(one-dimensional–zero-dimensional [1D–0D]) organic lead iodide withwell-defined crystallinity. The fabricated single-crystal devices demonstratehigh-sensitivity photoresponse and x-ray detection performance. By spatiallyisolating organic molecules to form the mixed 1D–0D crystal structure, ionmigrations is effectively suppressed, resulting in a remarkable three orders ofmagnitude reduction in the dark current (56.4 pA @200 V) of the single-crystaldevices. Furthermore, by enhancing the background characteristics, weachieved an impressive low x-ray detection limit of 154.5 nGys^(-1) in the singlecrystaldevice. These findings highlight that the mixed 1D–0D organic leadiodide configuration efficiently controls ion migration within the crystal structure,offering a promising avenue for realizing high-performance perovskitebasedphotodetectors and x-ray detectors.

Distribution of Na+and Mechanical Properties of Hardened Body of Alkali-activated Cementitious Materials

To explore the distribution of and the mechanical properties(compressive strength)of the hardened body of alkali slag-fly ash cementitious materials,this study was conducted by using the XRD,FTIR,SEM/EDS,and other test methods in three conditions:airtight drying(AD),airtight immersion(AI),and airtight soaking(AS).The 1D distribution law of free of hardened body under standard curing conditions was explored.The experimental results show that under standard curing conditions,the 1D distribution of within 0d-3 d shows a∨-shaped distribution,within 3-7 d show a∧-shaped distribution,and within 7-28 d tends to be balanced.The test results of leaching rate show that the free was the most stable under AD conditions and the hardened body bound the most by XRD,FTIR and SEM/EDS.And the compressive strength of the hardened body was the highest.The compressive strength of 28th reached 95.9 MPa.The definite distribution of provides an important reference for the strength development and durability evaluation of the hardened body of alkaliexcited cementitious materials.

Unveiling the key factor affecting the illumination deterioration and response measures for lead halide perovskite solar cells

So far,it's been widely acknowledged that the Pb I2decomposition under illumination mainly accounts for the degradation of perovskite solar cells(PSCs)under maximum power point(MPP)tracking condition.However,PSCs without excess Pb I2were also reported to deteriorate rapidly under the same condition.Here,we demonstrate that the key to enhance PSCs stability under MPP tracking condition is not to have fascinating surface morphology with effective suppression of nonradiative recombination traps but to prevent the migration of iodine ion(I-)under light illumination.By partially substituting methylammonium chloride(MACl)with methylammonium iodide(MAI)and simutaneouly introducing I2during the sequential deposition,the iodine vacancies in perovskite films are substantially suppressed,thereby limiting the pathways for I^(-)migration.As a consequence,PSCs with efficiency of 24.28%are fabricated with remarkably enhanced working stability.

Facile construction of a multilayered interface for a durable lithium‐rich cathode

Layered lithium-rich manganese-based oxide(LRMO)has the limitation of inevitable evolution of lattice oxygen release and layered structure transformation.Herein,a multilayer reconstruction strategy is applied to LRMO via facile pyrolysis of potassium Prussian blue.The multilayer interface is visually observed using an atomic-resolution scanning transmission electron microscope and a high-resolution transmission electron microscope.Combined with the electrochemical characterization,the redox of lattice oxygen is suppressed during the initial charging.In situ X-ray diffraction and the high-resolution transmission electron microscope demonstrate that the suppressed evolution of lattice oxygen eliminates the variation in the unit cell parameters during initial(de)lithiation,which further prevents lattice distortion during long cycling.As a result,the initial Coulombic efficiency of the modified LRMO is up to 87.31%,and the rate capacity and long-term cycle stability also improved considerably.In this work,a facile surface reconstruction strategy is used to suppress vigorous anionic redox,which is expected to stimulate material design in high-performance lithium ion batteries.

TEM STUDIES FOR DIGM IN Kr ION IRRADIATED Au-Cu BILAYERS

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DEGRADATION DUE TO ENERGY PULSE IN HIGH-ENERGY ZnO VARISTORS

The degradation phenomena due to the energy pulse in the high-energy ZnO varistors used for deexitation and overvoltage protection of hydroelectric generator are investigated. The energy pulse, obtained by releasing the energy stored in an inductor, can be equivalent to the combination of the DC field components and the energy component. The variations of the characterized voltages, nonlinear coefficients and pre-breakdown V-A characteristics, increase with the number of the applied energy pulse. The asymmetrical variations of the electric properties of the high-energy ZnO varistors after the energy pulse arise from the deformation of the double Schottky barriers due to the ion migration occuring in the depletion layer and in the grain boundary.