Charge carrier dynamics in different crystal phases of CH_(3)NH_(3)PbI_(3)perovskite

Despite that organic-inorganic lead halide perovskites have attracted enormous scientific attention for energy conversion applications over the recent years,the influence of temperature and the type of the employed hole transport layer(HTL)on the charge carrier dynamics and recombination processes in perovskite photovoltaic devices is still largely unexplored.In particular,significant knowledge is missing on how these crucial parameters for radiative and non-radiative recombinations,as well as for efficient charge extraction vary among different perovskite crystalline phases that are induced by temperature variation.Herein,we perform micro photoluminescence(pPL)and ultrafast time resolved transient absorption spectroscopy(TAS)in Glass/Perovskite and two dierent Glass/ITO/HTL/Perovskite configurations at temperatures below room temperature,in order to probe the charge carrier dynamics of different perovskite crystalline phases,while considering also the effect of the employed HTL polymer.Namely,CH_(3)NH_(3)Pbb films were deposited on Glass,PEDOT:PSS and PTAA polymers,and the developed Glass/CH_(3)NH_(3)PbI_(3)and Glass/ITO/HTL/CH_(3)NH_(3)PbI_(3)architectures were studied from 85 K up to 215 K in order to explore the charge extraction dynamics of the CH_(3)NH_(3)PbI_(3)orthorhombic and tetragonal crystalline phases.It is observed an unusual blueshift of the bandgap with temperature and the dual emission at temperature below of 100 K and also,that the charge carrier dynamics,as expressed by hole injection times and free carrier recombination rates,are strongly depended on the actual pervoskite crystal phase,as well as,from the selected hole transport material.

PRECIPITATION AND GROWTH OF PEROVSKITE PHASE IN TITANIUM BEARING BLAST FURNACE SLAG

The effects of transformation of slag composition and additive agents on the morphology, the precipitation behavior, the crystal growth, and the volume fraction (VF) of perovskite (CaO·¤TiO_2) crystal in the Ti-bearing blast furnace slags were investigated. As the morphology of perovskite is dispersed in molten slags, the crystal growth mechanism of the melting of fine dendrites and the coarsening of large grains exist throughout the solidification of molten slags. With the increase of CaO and Fe_2O_3 content, VF of perovskite obviously increases. However, high basicity leads to the viscosity of slag, which results in the reduction of the average equivalent diameter (AED). The experimental results showed that the presence of the additives CaF_2 and MnO efficiently decreased the viscosity of the slags, and obviously improved the morphology of perovskite and promoted its growth.

Low Temperature One Step Synthesis of Barium Titanate: Particle Formation Mechanism and Large-scale Synthesis

The formation of BaTiO3 nanoparticles via the reaction of BaCl2, TiCl4 and NaOH in aqueous solution has been systematically studied. The formation of BaTiO3 from the ionic precursors has been elucidated to be a very rapid process, occurring at temperature higher than 60℃. Furthermore, the particle size could be controlled by the proper selection of the synthesis conditions (e.g. reactant concentration of 0.5—1.0mol·L-1, temperature of 80— 95℃ and pH≥13). A two-step precipitation mechanism was proposed. The first stage of the synthesis involved the formation of amorphous Ti-rich gel phase. The second stage of the synthesis was the reaction between the amor-phous phase and the solution-based Ba2+ ions, which led to the crystallization of BaTiO3. Based on the particle for-mation mechanism, a novel method, high gravity reactive precipitation, was proposed and used to mass production of BaTiO3 of average particle size of about 60 nm and with narrow particle size distribution. Because it could break up the amorphous Ti-rich gel into small pieces, intensify mass transfer, promote the reaction rate of amorphous Ti-rich gel with Ba2+ ions.

Low Temperature One-Step Synthesis of Barium Titanate:Thermodynamic Modeling and Experimental Synthesis

A thermodynamic model has been developed to determine the reaction conditions favoring low temperature direct synthesis of barium titanate (BaTiO3). The method utilizes standard-state thermodynamic data for solid and aqueous species and a 0ebye-Huckel coefficients model to represent solution nonideality. The method has been used to generate phase stability diagrams that indicate the ranges of pH and reagent concentrations, for which various species predominate in the system at a given temperature. Also, yield diagrams have been constructed that indicate the concentration, pH and temperature conditions for which different yields of crystalline BaTiO3 can be obtained. The stability and yield diagrams have been used to predict the optimum synthesis conditions (e.g., reagent concentrations, pH and temperature). Subsequently, these predictions have been experimentally verified. As a result, phase-pure perovskite BaTiO3 has been obtained at temperature ranging from 55 to 85℃ using BaCl2, TiCl4 as a source for Ba and Ti, and NaOH as a precipitator.

Initial Study of Strontium Barium Niobate/Strontium Barium Titanium Ceramics through A Modified Sol-Gel

Barium strontium titanate niobate (BSTN) composite ceramics system following the general formula 0.5BaO·0.5SrO·0.5TiO2·0.5Nb2O6 was successfully prepared. The investigation is carried out through a modified sol-gel method. By controlling the viscosity of the sol solution to suspend the strontium barium niobate ceramic powder uniformly which had been made beforehand and the viscosity of the sol could be changed by adjusting the mixture ratio of the precursor. Powders obtained from dried gels were calcined at 800 ℃ for 3 h. The bulk ceramics obtained from the dried powders were sintered at the temperatures of 1250 and 1300 ℃ respectively. The results of the XRD and SEM indicated that the perovskite phase and the tungsten bronze phase could be coexisted stably in BSTN at both of these temperatures. The increasing of the sintering temperature was good for the crystal phase growing and the solubility of the two phases in the composite ceramics. And the theory of adulteration could be adopted to resolve the phenomena that sintering temperatures too high, which resulted in the crystalline grains growing singularly. Some problems were put forward to pay attention to this material research process.

Synthesis of (1-x)Pb[(Mg,Zn)_(1/3)Nb_(2/3)] O_3-PbTiO_3 DielectricCeramic Powder by a Coprecipitation Process

A coprecipitation method was used for preparation of 0.95Pb[(Mg0.8,Zn0.2) 1/ 3 Nb2 /3]O3-0.05PbTiO3(PMZN-PT),dielectric ceramic powder. X-ray powder diffraction and electron probe energy dispersive, X-ray analyzer revealed that the powder calcinated at 800℃ for 2 h is the PMZN-PT with 100% single perovskite phase, and the order of magnitude of atomic proportion of Mg to Zn reaches approximately 10: 1. In addition, the influence of Zn and Ti content on the perovskite phase and pyrochlore phase formation namely : 0.95Pb[(Mg1-x Znx) 1 /3Nb,2/3]O3 -0.05PbTiO3, (1-y)Pb[(Mg0.7Zn0.3) 1 /3Nb2 /3] O3-yPbTiO3 was also analysed.

Preparation and characterization of La_(1-x)Ce_xFe_(1-y-n)Co_yRu_nO_3 compounds

The mixed oxides La1 -xCexFe1-y-nCOyRunO3 were prepared by sol-gel method and used as catalysts for NO direct decomposition. The catalysts were characterized by DTA - TG, XRD, IR and BET. XRD analysis reveals that the samples are in a pure perovskite phase in 550 - 650 ℃, and catalyst structure keeps long else 20 decrease, and lattice parameters enhance when Ru is introduced. The characteristic peaks of samples are stronger during a temperature increase, and the particle size grows faster. IR analysis shows that the position and shape of adsorption peaks are almost the same among all samples, but with the Ru content increasing, 600 cm^-1 peak stretches to a high frequency and changes to disorder. The wave numbers move to low frequency when n = 0. 05, yet it doesn＇ t vary obviously when n 〉 0. 05. The BET surface area testifies that particle sizes of all catalysts increase with temperature increasing.

Nonvolatile control of transport and magnetic properties in magnetoelectric heterostructures by electric field

Nonvolatile manipulation of transport and magnetic properties by external electric field is significant for information storage. In this study, we investigate the electric field control of resistance and magnetization in a magnetoelectric heterostructure comprising an electronic phase-separated La0.325Pr0.3Ca0.375MnO3（LPCMO） thin film and a ferroelectric（011）-oriented 0.7Pb（Mg1/3Nb2/3）O3-0.3PbTiO3（PMN-PT） substrate. In a room-temperature poled sample, the metal-toinsulator transition temperature of an LPCMO film increases and the resistance decreases with variation in the effect of the remnant strain. Meanwhile, the increase in the magnetization of the sample is observed as well. This effect would be beneficial for the development of novel storage devices with low power consumption.

Ion Migration and Accumulation in Halide Perovskite Solar Cells

Comprehensive Summary The halide perovskite semiconductors-based solar cells(PVSCs)show great promise as next-generation renewable energy sources,with the merits of low cost,high performance,good flexibility,etc.A major difference distinguishing the perovskite semiconductors from others lies in their ionic feature.This intrinsic property induces“freely-moving”ions to migrate and accumulate in the perovskite films and devices under different external stresses.As a charge carrier,these processes will strongly couple with the electronic process,and dramatically affect the performance and stability of PVSCs.This review summarizes and discusses the recent progresses and fundamental understandings of ion migration and accumulation behaviors in PVSCs.First,the basic principles of the general ion migration are reviewed.Second,following the fundamental understandings,the critical factors,e.g.,ion migration activation energy,ion density,ion diffusion coefficient,etc.,are extracted to understand the ion migration and accumulation in perovskite film.Third,the principles governing ion accumulation behaviors under different external stresses are discussed.Finally,the effect of ion migration and accumulation on band bending,and device performance is presented.Therefore,we hope this review provides a tutorial and insightful perspective regarding the most prominent ionic feature of perovskite semiconductors and their application for photovoltaics.

Iridium-Doped 10H-Phase Perovskite BaCo_(0.8)Fe_(0.15)Ir_(0.05)O_(3-δ)as an Efficient Oxygen Evolution Reaction Catalyst

Designing low-cost and high-performance catalysts of electrocatalytic oxygen evolution reaction(OER)has always been one of the hot topics in current research.Hexagonal perovskite materials show great application potential in this field.Here,we synthesized 5%Iridium(Ir)-doped hexagonal phase perovskite BaCo_(0.8)Fe_(0.15)Ir_(0.05)O_(3–δ)(BCFI).Using the Rietveld method to refine the structure,combining with the spherical aberration corrected high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)atomic imaging,we found that BCFI is a ten-layer hexagonal(10H)structure,which belongs to the Purn:x-wiley:1001604X:media:cjoc202200200:cjoc202200200-math-0001m2 space group.In addition,BCFI shows excellent OER catalytic effect and good stability in 1 mol/L KOH solution,and the overpotential reaches 294 mV at a current density of 10 mA cm^(–2).The reduction of Cobalt(Co)valence state induced by Ir doping significantly enhances the OER activity of BCFI.Meanwhile,density functional theory(DFT)calculations show that the 2p-band center of oxygen(O)in BCFI is closer to the Fermi level than that in undoped BaCo_(0.8)Fe_(0.15)Ir_(0.05)O_(3–δ)(BCF),which is beneficial to the OER.This work reveals a novel 10H-BCFI material with excellent OER performance,and provides a basis for the design of hexagonal perovskite materials in OER and other energy conversion fields.

A-site Cation Defects(Ba_(0.5)Sr_(0.5))_(1-x)Co_(0.8)Fe_(0.2)O_(3-δ)Perovskites as Active Oxygen Evolution Reaction Catalyst in Alkaline Electrolyte

Main observation and conclusion Perovskites(Ba_(0.5)Sr_(0.5))_(1-x)Co_(0.8)Fe_(0.2)O_(3-δ)(x=0.02,0.05,0.1 denoted as BSCF-0.98,BSCF-0.95,BSCF-0.9,respectively)with A-site cation defects are synthesized by simple and efficient sol-gel method and are proved to have better OER catalytic effect than the well-known(Ba_(0.5)Sr_(0.5))_(1-x)Co_(0.8)Fe_(0.2)O_(3-δ)(BSCF)oxides.BSCF-0.95 exhibits the best OER catalytic activity in the series perovskite.The current density of BSCF-0.95 is about 56%higher than that of BSCF oxide at a potential of 1.7 V.The experimental studies have shown that compared with BSCF,BSCF-0.95 oxide has a larger electrochemical surface area(ECSA),a higher content of O_(2)^(2–)species related to surface oxygen vacancies,and faster charge transfer rate,which may be the factors for the enhancement of OER activity.The theoretical calculation results prove that the center positions of the O 2p-band of perovskite with A-site cation defects are closer to the Fermi level than BSCF oxide,which agrees with the OER performance trend of the material.

Recent Application and Progress of Metal Halide Perovskite Photodetector on Flexible Substrates

In recent years,flexible photodetectors(FPDs)have received increasing attention due to their applications in electronic eyes,flexible sensing,terminal devices,and wearable devices.In addition,metallic halide perovskite materials are considered as future materials for FPDs due to their compatibility with flexible substrates,low cost,simple synthesis methods,and superior optoelectronic properties.This review provides a comprehensive overview of the relevant cutting-edge research in the field of flexible perovskite photodetectors(FPPDs)from 2020 to 2022.First,the evaluation criteria for FPPDs are discussed and the development of perovskite stability criteria is emphatically described.Afterwards,the synthesis methods and device construction processes of metal halide perovskite materials commonly used by researchers in the past three years are described.These include single crystals and low-dimensional materials.Moreover,we have elaborated on the research of self-powered FPPD and its contributions in wearability,terminals,and portability.Finally,a summary of developments and possibilities in the field of FPPDs from 2020 to 2022 is provided.

Recent Advances of Monolithic All-Perovskite Tandem Solar Cells:From Materials to Devices

Organic-inorganic metal-halide perovskite solar cells(PerSCs)have achieved significant progresses due to their outstanding optoelectronic charac-teristics,and the power conversion efficiency(PCE)of single-junction PerSCs has been boosted from 3.8%to a certified 25.2%.However,the efficien-cy of single-junction cells is governed by the Shockley-Queisser(S-Q)radiative limit,and fabricating all-perovskite tandem solar cells is a particularly attractive method to break the S-Q limit.Since the bandgap of lead(Pb)-based mixed halide perovskite can be tuned from 1.55 eV to 2.3 eV,and the mixed tin(Sn)-Pb perovskites have bandgap of~1.2 eV,these perovskites become the best candidates for the front and rear subcells of all-perovskite tandem device,respectively.In this review,we firstly summarize the current development progresses of two-terminal(2-T)all-perovskite tandem so-lar cells.For further optimizing the device performance,the wide bandgap mixed halide perovskites for front subcell,mixed Sn-Pb narrow bandgap perovskites for rear subcell,and the interconnection layer(ICL)of 2-T tandem device are then discussed.This review aims to open a pathway to real-ize highly efficient all-perovskite tandem solar cells.

Large bandgap oscillations in two-dimensional Dion–Jacobson phase perovskites caused by coherent longitudinal acoustic phonons [Invited]

Two-dimensional Dion–Jacobson(D-J)phase perovskites are prospective photovoltaic and optoelectronic materials.To study their mechanical properties and carrier-lattice interactions,we conduct femtosecond spectroscopic experiments on the films of a D-J perovskite.After optical excitation,a∼33 meV bandgap oscillation is observed in the film by transient absorption spectroscopy.With the help of transient reflection methods,we reveal that the oscillation originates from the transport of coherent longitudinal acoustic phonons through the film.Large bandgap oscillation indicates a strong coupling between carriers and lattice,and significant bandgap modulation by strains in D-J perovskites.

Sequential deposition method fabricating carbonbased fully-inorganic perovskite solar cells

Hybrid organic-inorganic halide perovskite material has been considered as a potential candidate for various optoelectronic applications. However, their high sensitivity to the environment hampers the actual application.Hence the technology replacing the organic part of the hybrid solar cells needs to be developed. Herein, we fabricated fullyinorganic carbon-based perovskite CsPbBr_3 solar cells via a sequential deposition method with a power conversion efficiency of 2.53% and long-time stability over 20 d under ambient air conditions without any encapsulation. An evolution process from tetragonal CsPb_2Br_5 to CsPb_2Br_5-CsPbBr_3 composites to quasi-cubic CsPbBr_3 was found, which was investigated by scanning electron microscopy, X-ray diffraction spectra, UV-vis absorption spectra and Fourier transform infrared spectroscopy. Detailed evolution process was studied to learn more information about the formation process before10 min. Our results are helpful to the development of inorganic perovskite solar cells and the CsPb_2Br_5 based optoelectronic devices.

Critical parameters near the ferromagnetic-paramagnetic phase transition in La_(0.67–x)Y_xBa_(0.23)Ca_(0.1)MnO_3 compounds(x=0.10 and x=0.15)

The critical properties of the mixed manganite La0.67–x Y x Ba0.23Ca0.1Mn O3 with x=0.10 and x=0.15 around the paramagnetic（PM）-ferromagnetic（FM） phase transition were investigated through various techniques. These involved modified Arrott plots, Kouvel-Fisher method and Widom scaling relation. Magnetic data, analyzed in the critical region, using the above methods, yielded the critical exponents for（x=0.10） La0.57Y0.10Ba0.23Ca0.1Mn O3（β=0.312±0.002 and γ=1.147±0.003 at T C=299.23±0.05 K）. Moreover, the estimated critical exponents of（x=0.15） La0.52Y0.15Ba0.23Ca0.1Mn O3 were β=0.286±0.004 and γ=0.943±0.002 at T C=289.53±0.06 K. The critical exponents＇ values were close to the theoretical values of 3D-Ising model and tricritical mean-field model. These results suggested that the present composition should be close to a tricritical point in the La0.67–x Y x Ba0.23Ca0.1Mn O3 phase diagram. Expressing the field dependence as ΔS M∝H n allowed us to establish a relationship between the exponent n and the critical exponents of the material and to propose a phenomenological universal curve for the field dependence of ΔS M.