Perovskites Research Papers - Academia.edu (original) (raw)

Heteroepitaxy—atomically aligned growth of a crystalline filmatop
a different crystalline substrate—is the basis of electrically driven
lasers, multijunction solar cells, and blue-light-emitting diodes1–5.
Crystalline coherence is preserved even when atomic identity is
modulated, a fact that is the critical enabler of quantum wells, wires,
and dots6–10. The interfacial quality achieved as a result of heteroepitaxial
growth allows new combinations of materials with complementary
properties, which enables the design and realization of
functionalities that are not available in the single-phase constituents.
Herewe showthat organohalide perovskites and preformed colloidal
quantum dots, combined in the solution phase, produce epitaxially
aligned ‘dots-in-a-matrix’ crystals. Using transmission electron
microscopy and electron diffraction,we reveal heterocrystals as large
as about 60 nanometres and containing at least 20 mutually aligned
dots that inherit the crystalline orientation of the perovskite matrix.
The heterocrystals exhibit remarkable optoelectronic properties
that are traceable to their atom-scale crystalline coherence: photoelectrons
and holes generated in the larger-bandgap perovskites
are transferred with 80% efficiency to become excitons in the
quantum dot nanocrystals, which exploit the excellent photocarrier
diffusion of perovskites to produce bright-light emission
from infrared-bandgap quantum-tuned materials. By combining
the electrical transport properties of the perovskite matrix with the
high radiative efficiency of the quantum dots, we engineer a new
platform to advance solution-processed infrared optoelectronics.

- by and +1
- •
- Perovskites, Colloidal Quantum Dots

The formation of solid solutions of the type [Ba(HOC2H4OH)4][Ti1−x Gex (OC2H4O)3] as Ba(Ti1−x /Gex )O3 precursors and the phase evolution during thermal decomposition of [Ba(HOC2H4OH)4][Ti0.9Ge0.1(OC2H4O)3] (1) are described herein. The 1,2-ethanediolato complex 1 decomposes above 589 °C to a mixture of BaTiO3 and BaGeO3. A heating rate controlled calcination procedure, up to 730 °C, leads to a nm-sized Ba(Ti0.9/Ge0.1)O3 powder (1a) with a specific surface area of S = 16.9 m2/g, whereas a constant heating rate calcination at 1,000 °C for 2 h yields a powder (1b) of S = 3.0 m2/g. The shrinkage and sintering behaviour of the resulting Ba(Ti0.9/Ge0.1)O3 powder compacts in comparison with nm-sized BaTiO3 powder compacts (2a) has been investigated. A two-step sintering procedure of nm-sized Ba(Ti0.9/Ge0.1)O3 compacts (1a) leads, below 900 °C, to ceramic bodies with a relative density of ≥90%. Furthermore, the cubic ⇆ tetragonal phase transition temperature has been detected by dilatometry, and the temperature dependence of the dielectric constant (relative permittivity) has also been measured.

- by Roberto Köferstein
- •
- Sintering, Synthesis of nanoparticles, Composites, Precursors research

Electronic structure calculations of cubic SrTiO3 and SrHfO3 are presented. The full-potential linear augmented-plane-wave method is used and exchange-correlation effects are treated by the local-density approximation. The tendency to ferroelectricity of both compounds is explored and compared by displacing the transition metal atom (Ti or Hf) towards one of the oxygens (001 direction). The calculations show that ferroelectricity is favored in SrTiO3 with respect to SrHfO3 and that this fact may be correlated with the degree of hybridization between transition metal d-O p bands as has been found for other related systems. Also a detailed discussion of the calculated electric field gradients is presented.

The lack of optical constants information for hybrid perovskite of CH 3 NH 3 PbBr 3 in thin films form can delay the progress of efficient LED or laser demonstration. Here, we report on the optical constants (complex refractive index and dielectric function) of CH 3 NH 3 PbBr 3 perovskite thin films using spectroscopic ellipsometry. Due to the existence of voids, the refractive index of the thin films is around 8% less than the single crystals counterpart. The energy bandgap is around 2.309 eV as obtained from photoluminescence and spectrophotometry spectra, and calculated from the SE analysis. The precise measurement of optical constants will be useful in designing optical devices using CH 3 NH 3 PbBr 3 thin films.

- by Elhadj Marwane Diallo and +1
- •
- LED Lighting, Perovskites, Band Gap, Spectroscopic Ellipsometry
- by Diego Ortiz
- •
- Engineering, Chemistry, Quantum Chemistry, Optimization
- by Dariusz Bochenek
- •
- Ferroelectrics, Perovskites, Mathematical Sciences, Physical sciences

Catalytic reforming of methane using carbon dioxide as the oxidant (Eqn. 1) is a reaction of great interest for the production of synthesis gas (H2 + CO), since in addition to generating an important chemical feedstock it simultaneously consumes two greenhouse gases. There is particular interest, as well as significant challenges, in combining it with the generation of biogas (CH4 + CO2) through the anaerobic digestion of biomass, a process that is currently significantly underutilised.
CH4 + CO2 ⇌ 2H2 + 2CO (1)
Research into the generation of electricity by direct reforming of methane using carbon dioxide in solid oxide fuel cells has been steadily increasing over the last few years, with much of the focus on using nickel supported yttria stabilised zirconia anodes [1,2]. These materials, however, suffer from severe lifetime issues due to unwanted carbon deposition caused by side reactions (Eqns. 2 and 3) and limited tolerance to sulphur that result in deactivation and limit their commercial viability. This solid formation of carbon blocks catalytically active sites and disrupts fuel distribution at the anode as well as breaking anode micro structure eventually leading to cell failure.
CH4 ⇌ C + 2H2 (2)
2CO ⇌ C + CO2 (3)
An alternative approach to using conventional nickel cermet anodes is to use mixed oxide materials. However, typically such materials show low catalytic activity and poor selectivity towards synthesis gas formation, favouring total oxidation products. In this presentation we show a novel, hydrothermally synthesized perovskite material that reforms biogas with negligible levels of carbon formation regardless of excess methane in the reactant feed. This material has significantly lower tendency to form deleterious carbon without sacrificing reforming activity and has been shown to be catalytically stable for extended periods of time (Fig.1).

- by Samuel Evans
- •
- Hydrogen, Solid Oxide Fuel Cells, Biogas, Perovskites

We report the facile synthesis of cesium copper bromide (CsCuBr 3) in HBr solvent at room temperature. The perovskite material was successfully used as a sensor to detect the water contamination in di-methylformamide (DMF).

- by Muhammad Aamir and +1
- •
- Sensor, Perovskites
- by Robert Metzger
- •
- Superconductivity, Thin Films, Perovskites, Thin Film
- by Adriana Urda
- •
- Heterogeneous Catalysis, Dispersion, Perovskites, Catalyst

Nanograins of SmCoO3 are prepared by citric acid assisted sol-gel autocombustion route. The characterizations of crystal structure, surface morphology and electrical properties of SmCoO3 powder are done using XRD, HRSEM, FTIR and BDS. The structural evolution of SmCoO3 upon increasing the annealing temperature is followed using XRD and FTIR analyses. The powder sample contains polycrystalline grains with average size equal to 35 nm and orthorhombic perovskite structure with Pbnm space group. The vibrational bands observed in FTIR spectrum at 545 cm−1 and 439 cm−1 correspond to Co-O stretching modes in cobaltite system. HRSEM images of the sample show the formation of hexagonal shaped grains of samarium cobaltite. The AC electrical conductivity of 4.914 × 10−5 S cm−1 at 295 K is measured for SmCoO3 nanoparticles. The impedance spectra bring out the semiconducting behavior of the material.

- by Sathyamoorthy B
- •
- Nanomaterials, Structural Analysis, Perovskites, Dielectric Spectroscopy
- by Roushown Ali
- •
- Inorganic Chemistry, Calcium, Solid State Chemistry, Neutron Diffraction

: Perovskite solar cells are keeping a very high interest in the solar energy world, with an efficiency in constant
rise each year. In this study, we designed a tin-based (Hole Transport Material) HTM perovskite solar cell with the novel
architecture Au/CH3NH3SnI3/TiO2/ZnO: Al. A simulation has been carried-out by using the SCAPS-1D solar cell
capacitance simulator, which is well adapted to study the solar cell behavior. Through the software tool, we have studied
the absorber’s layer thickness effect and the model operating temperature by plugging many varied parameters. The
encouraging results of: 20.08% conversion efficiency, 32.76mA/cm² short-circuit current density (Jsc), 0.827 V open
circuit voltage (Voc), and a fill factor (FF) of 74.06%, are predicted with the obtained optimal parameters.
The results indicate the high aptitude of lead free & HTM perovskite to achieve high efficiency and become a good
alternative for the traditional solar cells in the future

- by Zeal Press
- •
- Solar Cells, Perovskites, SCAPS

Thermal annealing and precursor composition play critical roles in crystallinity control and morphology formation of perovskite thin films for achieving higher photovoltaic performance. In this study we have systematically studied the role of annealing temperature on the crystallinity of perovskite (CHNH3PbI3) thin films casted from single (without PbCl2) and mixed (with PbCl2) halide precursors. Higher annealing temperature leads to agglomeration of perovskite crystals. This explains that the effects of annealing temperature on the performance of perovskite solar cells are different in single and mixed halide processed films. It is observed that the perovskite crystallinity and film formation can be altered with the addition of lead chloride in the precursor solution. We report that single halide perovskite solar cells show no change in morphology and crystal size with increase in annealing temperature which was confirmed by UV-vis absorption spectroscopy, x-ray diffraction (XRD) and atomic force microscopy (AFM). However, mixed halide perovskite (CH3NH3PbI3-xClx) solar cells show significant change in crystal formation in the active layer when increasing annealing temperature. In addition, heating perovskite precursor solutions at 150 oC can lead to enhancement in solar cell efficiency for both single and mixed halide. Perovskite solar cells fabricated using heated precursor solutions forms dense film morphology, thus significantly improved fill factor up to 80% with power conversion efficiency exceeding 13% under AM 1.5 condition.

During the last few decades, and in some cases only the last few years, novel thin-ﬁlm photovoltaic (PV) technologies such as dye-sensitized solar cells (DSSC), organic solar cells (OPV), and, more recently, perovskite-based solar cells (PSC) have been growing in maturity with respect to device performance and device stability. Together with new material systems, novel device architectures have also been introduced. Both parameters will have an effect on the overall device stability. In order to improve the understanding of degradation effects and how they can be prevented, stress testing under different conditions is commonly applied. By careful combination of stress factors and thorough analysis of photovoltaic parameter decaying curves, an understanding of the underlying degradation pathways can be gained. With the help of standardized and accelerated stress tests, as described in the ISOS-protocols, statements concerning application lifetimes can ﬁ nally be made and compared among different labs. Once a photovoltaic technology has proven long lasting durability, the ultimate barrier for entering the commercial market are the IEC tests, taking a deeper look on overall safety and reliability, not only on durability. Here, the most prominent stress tests are reviewed, discussed and ciency, increased device life- extended with respect to learning the most about photovoltaic device stability

- by Elizabeth von hauff
- •
- Perovskites, Organic Photovoltaic
- by Devesh Sirothiya
- •
- Inorganic Chemistry, Crystal structure, Perovskites, X ray diffraction
- by Michael Lufaso
- •
- Analytical Chemistry, Protein Structure Prediction, Prediction, Optimization

Perovskite solar cells are a new breed of solar cells belonging to the third generation of innovations that have witnessed an efficiency boost from 3.8% to 25.5% in a time frame of 10 years. There are a number of manufacturing techniques known and discovered by man to maximize the possibility of scalability across all sectors. Each synthesizing technique emerges with its own set of pros and cons which need to be correspondingly tackled based on the application scenario. The research advancements currently being carried out are discovering materials that can be exploited to replace the current PSCs and overcome the challenges of these devices, band gap engineering, and revamping metal contacts and lastly, reducing toxicity of current PSCs are few of the varied research opportunities available in this domain of renewables.

- by Ankit Stephen Thomas.
- •
- Materials Science, Chemistry, Renewable Energy, Solar Cell

� (rGO)/La 0.9 Bi 0.1 FeO 3 (LBFO) nanocomposites were prepared by sol-gel method. � LFBO has a single-phase and were homogeneously dispersed on graphene nanosheets. � rGO improves the electrical properties up to 50 wt% of rGO. � The ferromagnetic behavior was detected and an enhancement of magnetic properties with rGO. � The magnetic and electrical properties can be optimized by tuning the content of rGO. A B S T R A C T Reduced graphene oxide (rGO)/La 0.9 Bi 0.1 FeO 3 (LBFO) nanocomposites were successfully prepared. The structure , morphology, electrical and magnetic properties were investigated by X-ray diffraction, high-resolution transmission electron microscope, impedance analyzer, and vibrating sample magnetometer, respectively. Results show that perovskites LFBO has a single-phase and were homogeneously dispersed on graphene nanosheets. rGO improves the electrical properties up to 50 wt% of rGO. The ferromagnetic behavior of nanocomposites was detected and also an enhancement of its magnetic properties with rGO content. These results reveal that the magnetic and electrical properties can be optimized by tuning the content of rGO.

- by A. M . Mansour
- •
- Magnetic Materials, Nanocomposites, Perovskites, Dielectric Spectroscopy
- by Michael Lufaso
- •
- Analytical Chemistry, Crystal structure, Perovskites, Long Range Order
- by shohifa hafida
- •
- Particle Physics, Ferroelectrics, Perovskites, Computations
- by E. Atamanik and +1
- •
- Condensed Matter Physics, Inorganic Chemistry, Structure, Crystal chemistry

and now in this era of technology, carbon has played a significant and very prominent role
in almost all fields of science and technology. So as an honour to this marvellous element,
we humans should know about its various forms of existence. In this review article, we
shed light on all possible carbon-allotropes; similarities in their synthesis techniques and the
starting materials; their wide range of possible availability; and finally, future perspectives
and applications. A brief introduction is given on the types, structures, and shapes of the allotropes
of carbon for a better understanding.

- by Karthik Ps
- •
- Carbon Nanotubes, Fullerenes, Perovskites, Plasma

While energy shortage is always an issue, the impending exhaustion of fossil fuel sources makes it an ever
increasingly pressing one. Photovoltaic technology brings hope in the struggle to alleviate this problem, but
no solar cell has yet fulfilled the requirements of the viability of large scale production together with high
efficiency and low cost. Fortunately, recently reported organic–inorganic halide perovskites, possessing
the desirable properties of a high absorption coefficient, a long charge diffusion length, an appropriate
band gap, and solution processability, show great potential for photovoltaic applications. Within a few
years, the power conversion efficiency of perovskite solar cells has increased from 3.8% to 19.3%.
Reports on new preparation methods and materials continue to emerge. While reviews have focused on
mechanisms, cell structures, preparation methods and materials applied, it is important to give a
combined overview of all these aspects. Furthermore, this review considers the newly reported
preparation methods and mechanisms and summarizes the applied materials for each function of these
solar cells.

- by Uday Kiran Doppalapudi
- •
- Perovskites

The influence of monovalent cation halide additives on the optical, excitonic, and electrical properties of CH3NH3PbI3 perovskite is reported. Monovalent cation halide with similar ionic radii to Pb2+, including Cu+, Na+, and Ag+, have been added to explore the possibility of doping. Significant reduction of sub-bandgap optical absorption and lower energetic disorder along with a shift in the Fermi level of the perovskite in the presence of these cations has been observed. The bulk hole mobility of the additive-based perovskites as estimated using the space charge limited current method exhibits an increase of up to an order of magnitude compared to the pristine perovskites with a significant decrease in the activation energy. Consequentially, enhancement in the photovoltaic parameters of additive-based solar cells is achieved. An increase in open circuit voltage for AgI (≈1.02 vs 0.95 V for the pristine) and photocurrent density for NaI- and CuBr-based solar cells (≈23 vs 21 mA cm−2 for the pristine) has been observed. This enhanced photovoltaic performance can be attributed to the formation of uniform and continuous perovskite film, better conversion, and loading of perovskite, as well as the enhancement in the bulk charge transport along with a minimization of disorder, pointing towards possible surface passivation.

- by Mojtaba Abdi-Jalebi and +2
- •
- Surface passivation, Photovoltaic Solar Cells, Perovskites, Nanoscale Materails and Devices

Nanostructured Fe3O4 nanoparticles were prepared by a simple sonication assisted co-precipitation method. Transmission electron microscopy, X-ray diffraction and BET surface area analysis confirmed the formation of ∼20 nm crystallites that constitute ∼200 nm nanoclusters. Galvanostatic charge–discharge cycling of the Fe3O4 nanoaprticles in half cell configuration with Li at 100 mA g−1 current density exhibited specific reversible capacity of 1000 mAh g−1. The cells showed stability at high current charge–discharge rates of 4000 mA g−1 and very good capacity retention up to 200 cycles. After multiple high current cycling regimes, the cell always recovered to full reversible capacity of ∼1000 mAh g−1 at 0.1 C rate.• A simple and inexpensive ultrasonic assisted co-precipitation route has been followed to make monodisperse Fe3O4 nanoparticles. • Anodes made from the Fe3O4 nanoparticles exhibit specific reversible capacity of ∼1000 mAh g−1. • The anodes could operate at a current density from 100 to 4000 mA gm−1 with coulombic efficiency of almost 100%. • The anodes showed excellent cyclic stability for at least 200 cycles without capacity fade, and returned to specific capacity of 1000 mAh gm−1 at 0.1 C after multiple high current charge–discharge cycles.

In the present attempt, we report modified features of structural, dielectric, magnetic and ferroelectric behaviour of BiFeO 3 (BFO) by perovskite-spinel composite approach. ZnFe 2 O 4 (ZFO) is used as spinel phase. The structural measurement of composite show anisotropically compression in the BiFeO 3 lattice with ZFO compositions and stimulates the variation in bond length, bond angle, tilting angle, electron density and resultant polarization. This affects on magnetic and dielectric behaviour of BFO. Room temperature magnetic measurement revealed enhancement of magnetization of BFO in composite, attributed to spin restructuring due to change in magnetic anisotropy, exchange energy and stress energy at interface with ZFO composition. There is around 7 times enhancement in magnetization as compared to pure BFO phase. Dielectric profile of composites shows decrease in dielectric constant as well as dielectric loss as compared to single phase BFO. P-E loop exhibits leaky ferroelectric behaviour of composite system with drop down in leakage current by 2 order of magnitude than pure BFO phase. Magnetic contributions of individual phases in composite are determined by Vegard Law while dielectric contributions are modelled by Maxwell-Garnett (MG) equation. The present work demonstrates that BFO-ZFO: perovskite-spinel composite approach to modify magnetic, dielectric and ferroelectric behaviour and to facilitate BFO as room temperature multiferroic system.

- by VISHWAJIT M GAIKWAD
- •
- Composites, Magnetic Materials, Multiferroics, Ferroelectrics

Methylammonium lead iodide perovskite solar cells (PSCs) based on a solution-processed ZnO electron transporting layer were systematically investigated at low-temperature operating conditions. The power conversion efficiency gradually improved from 14.2% to 15.5% as the temperature decreased from 298 to 253 K, mainly owing to increments of short circuit current density and open circuit voltage. In addition, the improvements in photocurrent related to the high charge carrier mobility, owing to the ideal non-dispersive charge transport and fast electron transport lifetime at low temperature. Strikingly, hysteresis was suppressed with decreasing temperature related to the inhibition or relatively slow of ionic migration at reversed poling direction. This finding shows promising result of PSCs working efficiently under low temperature condition.

- by Riski Titian Ginting
- •
- Hysteresis, Perovskites, Activation Energy, Low Temperature
- by Paolo Fedeli
- •
- Physics, Materials Science, Solid State Physics, Chemistry
- by Marcos A L Nobre and +1
- •
- Engineering, Microstructure, Manufacturing, Impedance Spectroscopy

Gd3+ ion-substituted manganese ferrite nanoparticles with the chemical formula MnGdxFe2-xO4 (x = 0.0, 0.05, and 0.1) were synthesized by sol–gel auto combustion method. Thermal stability of the as-prepared sample was analyzed using thermo gravimetric and differential thermal analysis (TG–DTA) and the result reveals that the prepared sample is thermally stable above 300 °C. Structural and morphology studies were performed using powder x-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Indexed PXRD patterns confirm the formation of pure cubic spinel structure. The average crystallite sizes calculated using Sherrer’s formula decreased from 47 nm to 32 nm and lattice constant was enhanced from 8.407 Å to 8.432 Å. The FTIR spectrum of manganese ferrite shows a high frequency vibrational band at 564 cm−1 assigned to tetrahedral site and a low frequency vibrational band at 450 cm−1 assigned to octahedral site which are shifted to 556 cm−1
and 439 cm−1 for Gd3+ substitution and confirm the incorporation of Gd3+ into manganese ferrite. SEM analysis shows the presence of agglomerated spherical shaped particles at the surface. Room temperature dielectric and magnetic properties were studied using broadband
dielectric spectroscopy (BDS) and vibrating sample magnetometry (VSM). Frequency dependent dielectric constant, ac conductivity and tan delta were found to increase with Gd3+ ion substitution. The measured values of saturation magnetization decrease from 46.6 emu g−1 to 41 emu g−1 with increase in Gd3+ concentration and coercivity decreases from 179.5 Oe to 143 Oe.

- by Sathyamoorthy B
- •
- Perovskites, Rare Earth Oxides, Oxide Perovskites

In this study the characteristics of two different kinds of La0.6Sr0.4Co0.2Fe0.8O3‌ (LSCF) powders, one in-house powder synthesized by a co-precipitation method and another purchased from the Fuel Cell Materials Co. (FCM Co., USA) were compared. The co-precipitated powder was prepared by using ammonium carbonate as the precipitant with a NH4+/NO3- molar ratio of 2 and calcination at 1000°C for 1 h. Phase composition, morphology and particle size distribution of powders were systematically studied using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and laser particle size analysis (LPSA), respectively. The synthesized and commercial LSCF powders were overlaid on an Yttria-stabilized zirconia (YSZ) electrolyte having a gadolinium-doped ceria (GDC) interlayer. Electrochemical Impedance Spectroscopy (EIS) measurements were carried out at various operating temperatures in the range of 600-850°C. XRD and FESEM analysis revealed that single phase nano-crystalline LSCF powder with a mean crystallite size of 14 nm and mean particle size of 90 nm was obtained after calcination at 1000°C. The presence of hard agglomerated particles larger than a few microns in the commercial powder and also sub-micron agglomerates in the co-precipitated LSCF powder might be related to the final mechanical milling process and high calcination temperature of powders, respectively. LPSA results showed an identical mean particle size of about 1.5μm for both LSCF powders. EIS results revealed almost identical polarization resistance for both LSCF powders.

The electrocatalytic oxygen evolution reaction (OER) on iron based perovskites with composition La1−xCaxFeO3−δ (0.0 ≤ x ≤ 1.0) in alkaline solution has been investigated. The perovskite samples were synthesized by combustion method. Energy dispersive spectroscopy and X-ray photoelectron spectroscopy were used to determine the bulk and the surface composition, respectively. The X-ray diffraction and iodometric titration method were employed to examine the phases and the oxidation state, respectively. It was observed that incorporation of calcium (Ca2+) ions in the lattice of LaFeO3 decreases the lattice parameters and the cell volume systematically as evaluated by Rietveld method. Furthermore, increase in the degree of Ca2+ substitution from 0.0 to 1.0, increases the average oxidation state of iron from Fe3+ to Fe4+ in addition to creating oxygen vacancies. The evaluation of OER kinetics on a rotating disk electrode setup suggests that incorporation of Ca2+ decreases the activity initially (0.0 ≤ x ≤ 0.4), but further substitution increases the activity. The maximum activity was observed for x = 1.0. This change in the OER activity suggests an interplay between the bond lengths and angles, oxygen vacancy and the average oxidation state of Fe.

- by Ravi Sankannavar
- •
- Rietveld refinement, Perovskites, Oxidation State, Water Electrolysis

Bi 1-x La x FeO 3 single-phase solid solution with 0 x 0.3 was obtained by mechanochemical synthesis and characterized by X-ray diffraction, FT NIR Raman spectroscopy and magnetic studies. The nanocrystalline powders of rhombohedrally distorted perovskite structure R3c were studied 'as synthesized' by mechanosynthesis and after annealing at 500 C for 1 h. The annealing, which resulted in recrystallization of the amorphous shell of the nanograins, was found to modify the external lattice modes of Bi 1-x La x FeO 3 and resulted in changes in the temperature variation of the magnetization.

- by Izabela Szafraniak-Wiza and +1
- •
- Magnetic Materials, Raman Spectroscopy, Multiferroics, X-ray Diffraction
- by Yabing Qi
- •
- Engineering, Materials Chemistry, Dye Sensitized Solar Cells, Thin film solar cells
- by Eva Unger
- •
- Perovskites, Perovskite Based Solar Cells

The phases formed in the ternary system (Na1/2Bi1/2)TiO3–Bi4Ti3O12–BaTiO3 (NBT–BTO–BT) were studied at 1150°C in air. A very accurate picture of the ternary phase diagram was obtained examining almost 90 different compositions, exploiting low-angle XRD analyses to study the layer compounds. New compounds with five perovskite blocks (m=5) were discovered deep in the phase diagram. No compounds with m>5 were found. It was also established that pure perovskite compounds can be obtained only at compositions very close to the NBT–BT line. The relationships between the phases is discussed and it is hypothesized that the number of perovskite blocks in the system is determined by charged sites being created by the progressive substitution of Bi3+ in the A site of the perovskite blocks of BTO with the A cations of the perovskite end-member.

Photovoltaic applications of perovskite semiconductor material systems have generated considerable interest in part because of predictions that primary defect energy levels reside outside the bandgap. We present experimental evidence that this enabling material property is present in the halide-lead perovskite, CH 3 NH 3 PbI 3 (MAPbI 3), consistent with theoretical predictions. By performing X-ray photoemission spectroscopy, we induce and track dynamic chemical and electronic transformations in the perovskite. These data show compositional changes that begin immediately with exposure to X-ray irradiation, whereas the predominant electronic structure of the thin film on compact TiO 2 appears tolerant to the formation of compensating defect pairs of V I and V MA and for a large range of I/Pb ratios. Changing film composition is correlated with a shift of the valence-band maximum only as the halide−lead ratio drops below 2.5. This delay is attributed to the invariance of MAPbI 3 electronic structure to distributed defects that can significantly transform the electronic density of states only when in high concentrations.

- by Xerxes Steirer and +1
- •
- Perovskites

Organic−inorganic hybrid perovskite has appeared as one of the leading materials for realizing solution-based high-performing optoelectronic devices. The charge transport properties in this class of material are quite intriguing and still need to be carefully investigated. The temperature-dependent electrical property of methylammonium lead iodide (CH 3 NH 3 PbI 3) has been investigated by employing positron annihilation spectroscopy (PAS), which unambiguously reveals the gradual formation of open volume defects with the enhancement in temperature. The high-temperature ionic conductivity is due to the generation of both cationic (CH 3 NH 3 +) and anionic (I −) vacancies, possibly because of the elimination of methylammonium iodide (CH 3 NH 3 I) as identified from the coincidence Doppler broadening (CDB) of the positron annihilation spectroscopy. Further, the evolution of temperature-dependent defect density and corresponding electrical responses has been correlated with the structural phase transitions of CH 3 NH 3 PbI 3. This is the first ever report of temperature-dependent PAS measurement on hybrid lead halide perovskites to understand the nature and the origin of its electrical characteristics arising due to the variation in temperature.

- by Joydeep Dhar and +1
- •
- Perovskites
- by chau nguyen
- •
- Materials Engineering, Mechanical Engineering, Microstructure, Manufacturing
- by Joop Schoonman
- •
- Engineering, Nanomaterials, Perovskites, Chemical Analysis
- by MANASA K RATH
- •
- Perovskites, Electrochemical Impedance Spectroscopy, SOFC, XRD Crystallography

Being coexistence of at least two stable, simultaneous different orders (generally ferroelectricity and ferromagnetism and/or antiferromagnetism) in a single material due to the interaction between the two order parameters – namely, magnetization and electric polarization multiferroicity occurs. Those materials which show multiferroicity are known as Multiferroic magnetoelectric materials, which have received a considerable attention to the scientists and research community in recent years owing to their versatility and multi-functionality of these materials in various novel multifunctional devices as well as the understanding of fascinating fundamental physics due to the coupling of the two order parameters (i.e., magnetization and polarization).
Single phase ferroelectric nanomaterials, pure Barium Titanate (BaTiO3) (BTO), Cr-doped BTO (BaTi1−xCrxO3), Nd-doped BTO (Ba1−xNdxTiO3) are synthesized by solid state reaction process. The detailed microstructural analysis has been performed using XRHRD, FESEM, FTIR techniques. The Rietveld Refinement of the XRD data reveals the crystallinity of the samples. This divulges that the well crystallized samples are formed with tetragonal structure having ‘P4mm’ symmetry and the lattice parameter ‘a’ tended to decrease, while the lattice parameter ‘c’ tended to increase. A large value of the dielectric constant (~8000) and tan (δ) loss (0.124) are observed for pure BaTiO3 at room temperature at 100 Hz. We have found the transition temperature for pure BTO 403 K (130℃) which is 404 K (131℃) for BTCrO.

- by Arindam Samanta and +1
- •
- Synthesis of nanoparticles, FTIR spectroscopy, Nanoparticles, Multiferroics

We report on both the intrinsic and the extrinsic stability of a formamidinium lead bromide [CH(NH 2) 2 PbBr 3 = FAPbBr 3 ] perovskite solar cell that yields a high photovoltage. The fabrication of FAPbBr 3 devices, displaying an outstanding photo-voltage of 1.53 V and a power conversion efficiency of over 8%, was realized by modifying the mesoporous TiO 2 −FAPbBr 3 interface using lithium treatment. Reasons for improved photovoltaic performance were revealed by a combination of techniques, including photothermal deflection absorption spectroscopy (PDS), transient-photovoltage and charge-extraction analysis, and time-integrated and time-resolved photoluminescence. With lithium-treated TiO 2 films, PDS reveals that the TiO 2 −FAPbBr 3 interface exhibits low energetic disorder, and the emission dynamics showed that electron injection from the conduction band of FAPbBr 3 into that of mesoporous TiO 2 is faster than for the untreated scaffold. Moreover, compared to the device with pristine TiO 2 , the charge carrier recombination rate within a device based on lithium-treated TiO 2 film is 1 order of magnitude lower. Importantly, the operational stability of perovskites solar cells examined at a maximum power point revealed that the FAPbBr 3 material is intrinsically (under nitrogen) as well as extrinsically (in ambient conditions) stable, as the unsealed devices retained over 95% of the initial efficiency under continuous full sun illumination for 150 h in nitrogen and dry air and 80% in 60% relative humidity (T = ∼60 °C). The demonstration of high photovoltage, a record for FAPbBr 3 , together with robust stability renders our work of practical significance.

We have studied the diffuse scattering in the relaxor Pb(Mg1/3Nb2/3)O3 (PMN) using triple-axis neutron scattering techniques. The diffuse scattering first appears around the Burns temperature Td≈620K, indicating that its origin lies within the polar nanoregions (PNR’s). While the relative intensities of the diffuse scattering around (101), (200), and (300) are consistent with those previously reported by Vakhrushev et al., they are, surprisingly, entirely different from those of the lowest-energy transverse-optic (TO) phonon. This observation led Naberezhnov et al. to claim that this TO mode could not be the ferroelectric soft mode. However, a recent neutron study by Gehring et al. has unambiguously shown that the lowest-energy TO mode does soften on cooling and that the relative intensities are similar to those of PbTiO3. If the diffuse scattering in PMN originates from the condensation of a soft TO mode, then the atomic displacements of the PNR must satisfy the center-of-mass condition. But, the atomic displacements determined from diffuse scattering intensities do not fulfill this condition. To resolve this contradiction, we propose a simple model in which the total atomic displacement consists of two components δc.m. and δshift. Here δc.m. is created by the soft-mode condensation and thus satisfies the center-of-mass condition. On the other hand, δshift represents a uniform displacement of the PNR’s along their polar direction relative to the surrounding (unpolarized) cubic matrix. Within the framework of this model, we can successfully describe the neutron diffuse scattering intensities observed in PMN.

- by Peter Gehring
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- Neutron Diffraction, Dielectric Physics, Ferroelectrics, Perovskites

The electrical and optical properties of Ge-doped BaSnO3 ceramics sintered at various temperatures have been investigated to determine their semiconductor behavior. The electrical conductivity of Ge-doped BaSnO3 samples increases with increase in temperature, confirming that the samples exhibit a semiconductor behavior. A maximum conductivity value of 6.31 × 10−9 S/cm was observed for the sample sintered at 1200 °C. The optical band gaps of the Ge-doped BaSnO3 samples were determined by means of reflectance spectra. The variation of optical band gap with temperature was analyzed using Eg(T) = Ego + βT relation. The rate of change of the band gap β of BaSn0.99Ge0.01O3 was found to be 7.6 × 10−4 (eV/°C). A minimum optical band gap value of 2.95 eV was observed for the sample sintered at 1400 °C. It is evaluated that BaSn0.99Ge0.01O3 is a wide band gap semiconductor and its semiconducting properties change with sintering temperature.

- by Roberto Köferstein
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- Composites, Semiconductors, Composite Materials, Semiconductor Devices
- by Giuseppe Paternò and +2
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- Perovskites, Perovskite Based Solar Cells