Formation Of Perovskite Phase Research Articles

Approaching Full-Scale Passivation in Perovskite Solar Cells via Valent-Variable Carbazole Cations

Hybrid halide perovskite solar cells (PSCs) have emerged as the next-generation photovoltaic technology. Compared to steady silicon solar cells, PSCs are facilely processable but easily generate defects/traps during the thin-film fabrication from the solution. To passivate these defects, which have been considered as the origin of PSC instability, numerous large-sized organic cations (LSOCs) were applied via post-treatment methods. Unfortunately, along with the passivation on defects, these LSOCs could also react with regular perovskite phases and convert them into layered perovskite phases with poorer optoelectronic performances. Herein, we have designed carbazole ethylammonium iodide (CzEAI), a LSOC salt which exhibits a variation from monovalent to divalent state. Importantly, unlike traditional LSOC passivators in monovalent states mostly consumed by a regular perovskite phase and merely affecting the upper domain in thin films, CzEA in monovalent state could penetrate through the whole domain in perovskite films and then accurately convert into a divalent state at defect sites and thus realize a full-scale passivation in PSCs. Both simulation and experimental results proved that a CzEA passivator could overcome the formation of poor optoelectronic layered perovskite phases. As a result, the CzEA passivated PSC demonstrated an optimized photon-to-electron conversion efficiency (PCE) of 24.14% together with a significantly improved long-term stability over 5000 h.

Phase Distribution Manipulation through Molecular Interaction Enables Efficient Quasi-2D Perovskite Light-Emitting Diodes

Quasi-two-dimensional (quasi-2D) metal halide perovskites exhibit excellent electroluminescence (EL) performance promising for display and lighting applications, which benefits from the quantum and/or dielectric confinement effects as well as the unique energy-funneling process. However, the inefficient energy transfer caused by the intricate phase distribution with different thick nanoplatelets (n-values), as well as the existence of numerous defects, could deteriorate the EL performance of the resulting perovskite light-emitting diodes (PeLEDs). Here, a multifunctional small molecule, bistrifluoromethanesulfonimide lithium (LiTFSI), was introduced to address the above issues. The strongly electronegative fluorine atoms in LiTFSI form hydrogen bonding interactions with the ammonium heads of organic spacers, which suppress the formation of perovskite ultrathin nanoplatelet phases with small n-values, thus smoothing the energy transfer process. Meanwhile, the Lewis base sulfur oxide groups are capable of effectively passivating the uncoordinated lead ion defects and then reducing nonradiative recombination loss. Eventually, a green emission quasi-2D PeLED with an external quantum efficiency of 21.0% was achieved. This work provides a facile method to boost the performance of quasi-2D PeLEDs.

Ionic liquid functionalized tin halide perovskite investigated by STXM and spectro-ptychography

The structural and compositional properties of tin halide perovskites (CH(NH2)2SnI3, FASnI3) with and without an ionic liquid of 1-Ethyl-3-methylimidazolium bis(trifluormethylsulfonyl) imide (EMITFSI) were investigated using the scanning transmission soft X-ray microscopy (STXM) and spectro-ptychography techniques at the Sn M5,4-edge, I M5,4-edge, O K-edge, C K-edge, and N K-edge. The study offers a comprehensive interpretation of the spectral characteristics of main components (C, N, Sn, and I) in Sn-based perovskites through STXM-based techniques and further reveals differences between the perovskite samples with and without adding EMITFSI ionic liquid. The chemical imaging of Sn and I shows that the perovskite sample without ionic liquid has Sn-rich regions in iodine cavities, while the ionic liquid-treated sample exhibits a more homogeneous perovskite phase. Furthermore, the C and N K-edge XANES resonance features support the interaction between the non-volatile ionic liquid and FA+, thus playing a protective role in the formation and stabilization of perovskite phase.

Structure and Thermal-enhanced Magnetic Properties of Mn₄C Melt-spun Ribbons with Varied Stoichiometry

Cubic perovskite-type Mn4C is difficult to prepare for its metastable characteristics. In this work, we have obtained high-purity Mn₄C successfully by using melt-spinning method. The effects of stoichiometry on the structure and magnetic properties of the samples were studied systematically. We found that x = -0.1 is the optimum composition for the formation of the cubic perovskite phase in Mn4+xC during rapid quenching. Most MnSUB4+x/SUBC melt-spun ribbons with x other than -0.1 are composed of MnSUB23/SUBCSUB6/SUB, α-Mn, and Mn4C, while the fraction of different phase in MnSUB4+x/SUBC ribbons varies with x. The Curie temperature of MnSUB4+x/SUBC ribbons increases slightly with decreasing x, which may affect the lattice parameters of cubic Mn₄C and thus the Mn-Mn exchange interactions. The magnetization of MnSUB4+x/SUBC (x = -0.1 and 0) increases with increasing temperature in high-temperature region while the onset temperature for such behavior is dependent on the fraction of Mn₄C in the samples.

In Situ and Operando Characterizations of Metal Halide Perovskite and Solar Cells: Insights from Lab-Sized Devices to Upscaling Processes.

The performance and stability of metal halide perovskite solar cells strongly depend on precursor materials and deposition methods adopted during the perovskite layer preparation. There are often a number of different formation pathways available when preparing perovskite films. Since the precise pathway and intermediary mechanisms affect the resulting properties of the cells, in situ studies have been conducted to unravel the mechanisms involved in the formation and evolution of perovskite phases. These studies contributed to the development of procedures to improve the structural, morphological, and optoelectronic properties of the films and to move beyond spin-coating, with the use of scalable techniques. To explore the performance and degradation of devices, operando studies have been conducted on solar cells subjected to normal operating conditions, or stressed with humidity, high temperatures, and light radiation. This review presents an update of studies conducted in situ using a wide range of structural, imaging, and spectroscopic techniques, involving the formation/degradation of halide perovskites. Operando studies are also addressed, emphasizing the latest degradation results for perovskite solar cells. These works demonstrate the importance of in situ and operando studies to achieve the level of stability required for scale-up and consequent commercial deployment of these cells.

Electrochemical Performance of SrFeO3−δ for Application as a Symmetric Electrode in Solid Oxide Fuel Cells

SrFeO3−δ has been earlier reported to exhibit a large area-specific resistance even though it possesses high mixed ionic–electronic conductivity both in oxidizing and reducing conditions. The present study clarifies this aspect and investigates the defect chemistry and electrochemical performance correlations in SrFeO3−δ for the possible use as a symmetric electrode in solid oxide fuel cells. A conventional solid-state reaction method is adopted for powder synthesis. Structural characterization indicates an orthorhombic perovskite phase formation with a δ of 0.21. High dc electrical conductivities of ∼114.9 and 0.26 S·cm–1 are observed at 800 °C in air and reducing conditions, respectively. The area-specific resistance (ASR) for the SrFeO3−δ electrode is measured in a symmetrical half-cell configuration under various gas environments. At 800 °C, SrFeO3−δ offered low ASRs of 0.082, 0.055, and 0.122 Ω·cm2 in air, oxygen, and 3% H2O/H2, respectively. Although the ASR possesses excellent temporal stability in an oxidizing atmosphere, it increases to 0.42 Ω·cm2 after 100 h in reducing conditions owing to the brownmillerite phase formation. The redox cycling performance is also affected with the ASR rising from 0.13 to 0.24 Ω·cm2 at 800 °C in 3% H2O/H2 after 20 cycles. A maximum power density of 202 mW·cm−2 is achieved from the electrolyte-supported symmetric single cell based on the SrFeO3−δ electrodes at 800 °C. The results demonstrate the viability of using a SrFeO3−δ-based electrode for symmetrical solid oxide fuel cells.

Third order nonlinear optical properties and electrochemical performance of La2CoMnO6 double perovskite

La2CoMnO6 double perovskite was synthesized via modified combustion route. XRD with Rietveld refinement confirms monoclinic structure with space group of P21/n. Irregular shaped porous morphology was determined from FE-SEM and elemental analysis was done using EDAX spectra. Existence of mixed valence state of Co and Mn were verified by XPS spectra and its bandgap was determined using Tauc plot. Vibrational analysis validates the formation of perovskite phase and degeneracy in Raman modes/thermal broadening provides signature vibrational bands corresponding to stretching and bending motions of MnO6 and CoO6. Supercapacitor performance using La2CoMnO6 as electrode material exhibits 84% of cyclic stability after 500 cycles. The material exhibits a combined saturable and reverse saturable absorption behaviour under open aperture and self-defocusing nature due to thermal effect under closed aperture measurements with Z-scan method, using continuous wave irradiation. These findings confirmed that La2CoMnO6 manganite can be used for energy storage and photonic applications.

Modulation of nucleation and crystallization in PbI2 films promoting preferential perovskite orientation growth for efficient solar cells

PFAT promotes the secondary growth of PbI2 clusters and the early formation of favorable perovskite phases via a two-step sequential deposition approach.

Modification of a Buried Interface with Bulky Organic Cations for Highly Stable Flexible Perovskite Solar Cells

Flexible perovskite solar cells triggered a vast interest within the scientific community, thanks to their broad commercialization prospects. However, the stability of these devices still poses one of the major concerns on the way to rapid industrial deployment. Here, we demonstrate an effective strategy to improve the technical aspects of this technology, improving the reliability and efficiency values of these devices. We apply large organic ammonium molecules for modifying a buried interface between a hole-transporting layer (HTL) and perovskite-absorbing material. With the 4-fluorophenethylammonium iodide (FPEAI), we achieve 18.66% efficiency for the large-area (1 cm2) flexible solar cell, a significant improvement over the pristine device without modification. The applied passivation strategy results in a better hole extraction and reduced nonradiative recombination loss at the buried interface. Moreover, we demonstrate the formation of low-dimensional perovskite phases in the vicinity of the hole-transporting material upon the incorporation of large ammonium cations. This results in a significantly enhanced thermal and light-soaking stability of fabricated devices. We obtained no loss in 1000 h of aging at 85 °C, no loss in 1000 h of light soaking at open circuit, and less than 10% drop in 1000 h of operation at maximum power point for the optimized passivation treatment with the FPEAI. We also demonstrate a method for monitoring the structural stability of perovskite thin films upon prolonged illumination, ensued by the amount of molecular iodine being released from the layer.

Enhancement of magnetic and dielectric properties in (1-x).BEFO+ x.NZF nano composites

Nanostructured Bi0.9Eu0.1FeO3 (BEFO), Ni0.6Zn0.4Fe2O4 (NZF), and (1-x).BEFO + x.NZF composites have been synthesized by traditional solid state reaction process with several dispersion techniques, where x = 0.0, 0.1, 0.3, 0.5, 0.7 and 1.0. X-ray diffraction confirms the perovskite, cubic, and mixed perovskite-spinel phase formation of BEFO, NZF, and (1-x).BEFO + x.NZF composites respectively. FESEM and EDX analysis confirm the nano grain size and compositional purity of the samples. The effect of sintering temperature (TS) on grain growth was studied at 600 °C and 850 °C, where the range of the average grain size is between (90–131) nm and (157–272) nm. The magnetic hysteresis loop properties of all the samples were measured by VSM, where the saturation magnetization (MS) of BEFO increased from 10.31 emu/g to 50.54 emu/g with increasing NZF content. The increment of NZF content also modified other magnetic properties of (1-x).BEFO + x.NZF composites such as coercive force (HC), retentivity (Mr), magnetic moment (nB), and anisotropy constant (K). The frequency dependent permeability measurements show that the initial permeability (μ') was stable in a long frequency range up to 108 Hz and that the magnetic loss tangent (tanδM) decreased with increasing NZF content. The dielectric characteristics and AC resistivity of the composites were measured by an impedance analyzer over a wide frequency range (1 Hz–100 MHz). All the dielectric properties of the synthesized samples show excellent stability up to a long frequency region and vary sharply with increasing NZF content. From the optimization, 0.9 BEFO + 0.1 NZF composite has the highest permeability and dielectric values with the least amount of dielectric and magnetic losses. All the investigated composites might be strong candidates as multiferroic materials with strong magnetic and electric characteristics.

Crystal Clamping in (Ba, Sr)TiO3 Borosilicate Glass Ceramics

Background: Perovskite glass-ceramics have attracted the attention of researchers and scientists due to their wide range of applications in energy storage devices, solar cells, photovoltaic cells, etc. Barium titanate is the first discovered perovskite glass-ceramics. After the discovery of barium titanate, several perovskite glass-ceramics have been discovered. Several substitutions have also been attempted for the progress of perovskites. Barium strontium titanate is one of the perovskite glass-ceramics in which few barium ions are replaced by strontium ions. The crystal clamping is also found in a few perovskite glass-ceramics, e.g., PbTiO3. Aims: In the present investigation, our focus is on the synthesis and crystallization behavior of barium strontium titanate borosilicate glass-ceramics in glass system 64[(Ba1-xSrx).TiO3]- 30[2SiO2.B2O3]-5[K2O]-1[La2O3] (0.0 ≤ x ≤ 1.0). Methods: Synthesized glasses were characterized by differential thermal analysis, X-ray diffraction, and scanning electron microscopy. Results: The crystallization behavior showed the formation of major crystalline phase of BaTiO3/ BaSrTiO3/ Ba1.91Sr0.09TiO4/ SrTiO3 along with some pyrochlore phase of Ba2TiSi2O8/ Sr2TiSi2O8/ Ba2Ti2B2O9/ Sr2B2O5. The crystalline phase formation depends upon both composition and the crystallization process. The crystal clamping was attributed to synthesizing glass-ceramics samples during the crystallization. Conclusion: Bulk barium strontium titanate glass-ceramics were successfully prepared by the melt quench method. X-ray diffraction studies confirmed the formation of the major perovskite phase. During the crystallization of glasses, crystal clamping is attributed to the barium strontium titanate glass-ceramics.

Effect of Nd-doping on 0.95(K0.6Na0.4)NbO3-0.05(Bi0.5Na0.5)ZrO3 ceramics: Enhanced electrical properties and piezoelectric energy harvesting capability

Present work reports the influence of Nd-dopant on the structural, microstructural and di-/ferro-/piezo-electrical properties of lead-free binary piezoelectric perovskite system 0.95(K0.6Na0.4)NbO3-0.05(Bi0.5Na0.5)ZrO3 (abbreviated as KNN-BNZ). X-ray diffraction confirmed the formation of perovskite phase with coexisting tetragonal and rhombohedral phases for both the samples. The introduction of Nd3+ in KNN-BNZ resulted in reduced average grain size and curie phase transition temperature (from 347 °C to 294 °C at 1 kHz). Nd-doped KNN-BNZ ceramic showed enhanced piezoelectric response (d33 = 382 pC/N), well saturated P-E hysteresis loops (Ec = 15.27 kV/cm and Pr = 24.74 μC/cm2) with excellent fatigue stability and high pyroelectric coefficient (p ∼ 1418.4 μC/m2/oC). Based on the synthesized piezoceramics, piezoelectric energy harvesting devices were further fabricated and the open-circuit piezo-voltage from pure and Nd-doped KNN-BNZ based devices was measured to be 6.2 and 8.6 V, respectively. The obtained results highlight the candidature of Nd-doped KNN-BNZ ceramic for ferroelectric memory and mechanical vibration energy harvesting devices, as a substitute for lead based ferroelectric perovskites.

Synthesis, Structural and Raman Investigations of PbNi1/3Nb2/3O3 Ceramics

The Pb(Ni1/3Nb2/3)O3 (PNN) ceramics was synthesized by two different methods, viz. (i) single step and (ii) double step. Phase formation of powders prepared by both the methods at various temperatures and lead excess were analyzed by X-ray diffraction (XRD) and Raman scattering experiments. The studies revealed that for single step method the unreacted phases diminished with increase of firing temperature and only impure nickel niobate phase remained at 1200°C. Addition of 4 wt% excess lead oxide reduced the impure nickel niobate phase concentration from 8.9% to 4.2% for the single step method. Addition of 2 wt% excess lead oxide was found sufficient to remove pyrochlore nickel niobate phase for double step method. Temperature dependent XRD showed pure phase throughout the temperature range of 35 to 350 K indicating the stability of the phase formed. The Raman study also confirmed the formation of pure perovskite phase.

Structural, Morphologic, and Ferroelectric Properties of PZT Films Deposited through Layer-by-Layer Reactive DC Magnetron Sputtering

Lead zirconate titanate (PZT) is a widely used material with applications ranging from piezoelectric sensors to developing non-volatile memory devices. Pb(ZrxTi1−x)O3 films were deposited by DC reactive magnetron sputtering at a temperature range of (500–600) °C. X-ray diffraction (XRD) indicated the perovskite phase formation in samples synthesized at 550 °C, which agrees with Raman data analysis. Scanning electron microscopy (SEM) measurements supplemented XRD data and showed the formation of dense PZT microstructures. Further X-ray photoelectron spectroscopy (XPS) analysis confirmed that the Zr/Ti ratio corresponds to the Pb(Zr0.58Ti0.42)O3 content. Dielectric measurement of the same sample indicated dielectric permittivity to be around 150 at room temperature, possibly due to the defects in the structure. P-E measurements show ferroelectric behavior at a temperature range of (50–180) °C. It was found that the remnant polarization increased with temperature, and at the same time, coercive field values decreased. Such behavior can be attributed to energetically deep defects.

Mechanochemical Synthesis of Soft Ferromagnetic Perovskite Lanthanum Strontium Manganite (La0.6Sr0.4MnO3)

Nanocrystalline La0.6Sr0.4MnO3 sample with perovskite structure was successfully prepared by mechanochemical synthesis. Mechanical treatment for 10 h followed by annealing at 1100 °C results in the formation of single perovskite lanthanum strontium manganite (LSMO) phase with rhombohedral crystal structure and symmetry. The heat-treated sample crystallite size, calculated from X-ray diffraction pattern, was about 84 nm. The scanning electron microscope images indicated a high degree of fine structure. The formation of single perovskite phase was confirmed by FTIR measurements. The magnetic measurements showed the soft ferromagnetic behavior of the obtained sample. The saturation magnetization was found to be lower than that expected from theoretical calculation for perfect ferromagnetic ordering and lower than the saturation magnetization published for bulk sample. This was explained in the light of the core/shell model of manganite nanoparticles. The obtained sample was found to have a negative coefficient of magnetoresistance at room temperature of about (−3.5%) with the application of 25 kOe magnetic field.

Tuning Napththalenediimide Cations for Incorporation into Ruddlesden–Popper-Type Hybrid Perovskites

Layered hybrid organic–inorganic perovskite (LHOIP) materials constructed with low-band-gap chromophore-based organic spacer cations are an emerging class of materials that promise unique tunability of their optoelectronic properties. However, the large size of such chromophore-based spacer cations challenges their incorporation into a layered perovskite structure and requires further insight into the layered perovskite phase formation mechanism. Herein, we report the preparation and incorporation of asymmetric naphthalenediimide (NDI) spacer chromophore cations with different amine-bearing alkyl linker chains into thin films of LHOIPs. Using in situ UV–vis spectroscopic kinetic studies of the quantum well formation, we show that shorter linker chain lengths require higher annealing temperatures to form the LHOIP structure. Avrami analysis of the layered perovskite formation shows a larger Avrami coefficient (n = 3.64) for short linker chain-bearing cations compared to that for longer alkyl chain-bearing cations (n = 2.43), suggesting an evolution from three-dimensional to quasi-two-dimensional crystal growth with increasing linker chain length. Additionally, transient absorption spectroscopy and broad-band fluorescent upconversion spectroscopy indicate fast photoinduced charge transfer from the inorganic layer to the electron-accepting NDI-spacer cation.

LaCrO3-CeO2-Based Nanocomposite Electrodes for Efficient Symmetrical Solid Oxide Fuel Cells.

La0.98Cr0.75Mn0.25O3−δ–Ce0.9Gd0.1O1.95 (LCM-CGO) nanocomposite layers with different LCM contents, between 40 and 60 wt %, are prepared in a single step by a spray-pyrolysis deposition method and evaluated as both air and fuel electrodes for solid oxide fuel cells (SOFCs). The formation of fluorite (CGO) and perovskite (LCM) phases in the nanocomposite electrode is confirmed by different structural and microstructural techniques. The intimate mixture of LCM and CGO phases inhibits the grain growth, retaining the nanoscale microstructure even after annealing at 1000 °C with a grain size lower than 50 nm for LCM-CGO compared to 200 nm for pure LCM. The synergetic effect of nanosized LCM and CGO by combining their high electronic and ionic conductivity, respectively, leads to efficient and durable symmetrical electrodes. The best electrochemical properties are found for 50 wt % LCM-CGO, showing polarization resistance values of 0.29 and 0.09 Ω cm2 at 750 °C in air and H2, respectively, compared to 2.05 and 1.9 Ω cm2 for a screen-printed electrode with the same composition. This outstanding performance is mainly ascribed to the nanoscale electrode microstructure formed directly on the electrolyte at a relatively low temperature. These results reveal that the combination of different immiscible phases with different crystal structures and electrochemical properties could be a promising strategy to design highly efficient and durable air and fuel electrodes for SOFCs.

Differentiated Functions of Potassium Interface Passivation and Doping on Charge-Carrier Dynamics in Perovskite Solar Cells.

The inclusion of potassium in perovskite solar cells (PSCs) has been widely demonstrated to enhance the power conversion efficiency and eliminate the hysteresis effect. However, the effects of the locations K+ cations on the charge-carrier dynamics remain unknown with respect to achieving a more delicate passivation design for perovskite interfaces and bulk films. Herein, we employ the combined electrical and ultrafast dynamics analysis for the perovskite film to distinguish the effects of bulk doping and interfacial passivation of the potassium cation. Transient absorption spectroscopy indicates an enhancement of charge-carrier diffusion for K+-doped PSCs (from 808 to 605 ps), and charge-carrier transfer is significantly promoted by K+ interface passivation (from 12.34 to 1.23 ps) compared with that of the pristine sample. Importantly, K+ doping can suppress the formation of wide bandgap perovskite phases (e.g., FAPbI0.6Br2.4 and FAPbI1.05Br1.95) that generate an energy barrier on the charge-carrier transport channel.

Growth of Hybrid Perovskite Films via Single-Source Perovskite Nanoparticle Evaporation.

Herein, we demonstrate a vacuum-based evaporation approach to fabricate organic-inorganic perovskite thin films by using phase-formed halide perovskite nanoparticles (NPs) as a precursor/source. We are able to consistently obtain MAPbX3 (MA=CH3 NH3 and X=Cl, Br or I) thin films at various substrates (e. g., glass, ITO, or plastic). The perovskite phase formation in thin film form is confirmed by x-ray diffraction (XRD) studies. Small micro-strain (tensile) values of 1.64×10-3 , 1.42×10-3 and 6.85×10-4 obtained for MAPbCl3 , MAPbBr3 and MAPbI3 films respectively from Williamson-Hall equation indicate low structural distortions in perovskite thin films. The absorption spectra of thin films show sharp band edge having direct band gap, which is followed by narrow full width at half maxima (FWHM ∼0.1 eV) of the emission peak. Thin films of MAPbCl3 , MAPbBr3 and MAPbI3 show direct band gap of 3.1 eV, 2.4 eV and 1.6 eV, respectively. Small Urbach energy values of 33 meV, 44 meV and 66 meV for MAPbCl3 , MAPbBr3 and MAPbI3 films respectively indicates low defect density in various perovskite films. Scanning electron microscopy (SEM) along with energy-dispersive X-ray spectroscopy (EDS) shows high surface coverage and uniform chemical composition of MAPbX3 (X=Cl, Br and I) thin films deposited by the present method. We have successfully controlled the film thickness from 250 nm to 1 μm by varying the nanoparticle precursor amount. The perovskite thin films deposited by the present method are highly stable against the degradation under ambient conditions. Systematic XRD studies along with absorption data demonstrate that the MAPbCl3 and MAPbBr3 films stored under ambient conditions remained stable for more than 30 days and MAPbI3 films for more than 7 days.

Synthesis and the Study of Mechanism of Perovskite Formation of Pb (Fe0.5Nb0.5)O3 Ceramics

Abstract: Lead iron neobatePb(Fe0.5Nb0.5)O3 ceramics were prepared by using B-site precursor method. The formation of perovskite phase and microstructure are reported. The formation of B-site precursor and perovskite formation mechanism were studied by using X-ray diffraction and thermal analysis. Keywords: B-site precursor, pyrochlore, perovskite phase, PFN Ceramic