Perovskite Particles Research Articles

Dielectric response of vulcanized natural rubber containing BaTiO3 filler: The role of particle functionalization

Natural rubber (NR) nanocomposites have been prepared with hydroxylated barium titanate filler (BaTiO3-OH), employing emulsion polymerization followed by vulcanization process. The addition of barium titanate, a compound with high dielectric permittivity, was envisaged to increase the insulating properties of NR films, thereby reducing the electrical stress and the possibility of undesired arcing on their surfaces. The content of perovskite particles greatly affected both, the mechanical and the electrical properties, of the vulcanized films. It was observed that the optimum functionalized nanoparticle concentration is around 0.25–0.50 phr, range in which the elongation of break was maintained between 874–935% and the tensile strength was between 4.40–4.80 MPa; whereas the dielectric permittivity (ɛ′) is slightly lower than the pristine NR or the NR compounded with high content of BaTiO3 nanoparticles. The dielectric study revealed the presence of two dielectric relaxation modes: (i) glass to rubber transition (α-relaxation) and (ii) interfacial polarization (IP), known as Maxwell−Wagner−Sillars (MWS) polarization. The comparison between small concentrations of non-functionalized and functionalized BaTiO3 inside NR polymeric films lead to the conclusion that the dielectric breakdown strength is high for non-functionalized fillers, supposedly due to less IP polarization phenomena.

Evaluation of Electrochemical Properties of LSCF Electrode with GDC Barrier Layer under both Fuel Cell and H2O/CO2 Co-Electrolysis Modes

Nano LSF (La0.6Sr0.4FeO3-δ)-YSZ was prepared by infiltration process for both SOFC and SOEC modes. XRD pattern and SEM characterization had demonstrated that the nano-sized LSF perovskite particles were uniformly distributed onto the inner surface of the YSZ backbone. The electrochemical performances of the cell were evaluated for both power generation and steam electrolysis, during which humidified hydrogen gas and feed gas (50%H2O+25%H2+25%N2) were introduced, respectively. Furthermore, the electrochemical stability of the cell employing the LSF-YSZ composite electrode was investigated at 0.5 A*cm-2 and 0.8 A*cm-2 for fuel cell and steam electrolysis operation, respectively. Subsequently, SEM images of the post-test cells had exhibited that the LSF-infiltrated YSZ electrodes had no obvious structural variation. The results indicated that the cell with nano-LSF-YSZ electrode had shown high long-term stability for both fuel cell and electrolysis conditions.

Combined solvent and vapor treatment to prepare high quality perovskite films under high relative humidity

It is a great challenge to prepare high quality perovskite films in ambient atmosphere with high humidity (≥50%), since the commonly adopted two step sequential deposition process produces perovskite films with rough surfaces and a large amount of residual PbI2. To solve these problems, a facile method using combined solvent and vapor treatment is proposed. The residual PbI2 is diminished through a solvent treatment process, and then smooth perovskite surface with micrometer scaled perovskite particles is obtained with a CH3NH2 vapor treatment. The quality of the obtained perovskite films is examined in the hole transport material free perovskite solar cells, and power conversion efficiency is boosted up by 17.3% compared with the traditional method. When a CuPc hole transport layer is further introduced, carbon counter electrode based perovskite solar cells exhibit a superior power conversion efficiency of 16.61%. Thus this method shows great potential in further optimizing the performance of perovskite solar cells.

Highly Efficient Light-Emitting Diodes of Colloidal Metal-Halide Perovskite Nanocrystals beyond Quantum Size.

Colloidal metal-halide perovskite quantum dots (QDs) with a dimension less than the exciton Bohr diameter DB (quantum size regime) emerged as promising light emitters due to their spectrally narrow light, facile color tuning, and high photoluminescence quantum efficiency (PLQE). However, their size-sensitive emission wavelength and color purity and low electroluminescence efficiency are still challenging aspects. Here, we demonstrate highly efficient light-emitting diodes (LEDs) based on the colloidal perovskite nanocrystals (NCs) in a dimension > DB (regime beyond quantum size) by using a multifunctional buffer hole injection layer (Buf-HIL). The perovskite NCs with a dimension greater than DB show a size-irrespective high color purity and PLQE by managing the recombination of excitons occurring at surface traps and inside the NCs. The Buf-HIL composed of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) and perfluorinated ionomer induces uniform perovskite particle films with complete film coverage and prevents exciton quenching at the PEDOT:PSS/perovskite particle film interface. With these strategies, we achieved a very high PLQE (∼60.5%) in compact perovskite particle films without any complex post-treatments and multilayers and a high current efficiency of 15.5 cd/A in the LEDs of colloidal perovskite NCs, even in a simplified structure, which is the highest efficiency to date in green LEDs that use colloidal organic-inorganic metal-halide perovskite nanoparticles including perovskite QDs and NCs. These results can help to guide development of various light-emitting optoelectronic applications based on perovskite NCs.

Uniform PMMA-CH3NH3PbBr3 Nanoparticle Composite Film for Optoelectronic Application

Organometal halide perovskite materials, due to the tunability of their electronic and optical properties by control of composition and structure, have taken a position of significant importance in optoelectronic applications such as photovoltaic and lighting devices. Despite numerous studies on the structure - property relationship, however, practical application of these materials in electronic and optical devices is still limited by their processability during fabrication. Achieving nano-sized perovskite particles embedded in a polymer matrix with high loading density and outstanding photoluminescence performance is challenging. Here, we demonstrate that the careful control of nanoparticle formation and growth in the presence of poly(methyl methacrylate) results in perovskite nanoparticle - polymer nanocomposites with very good dispersion and photoluminescence. Furthermore, this approach is found to prevent further growth of perovskite nanoparticles, and thus results in a more uniform film, which enables fabrication using the perovskite nanoparticles.

Effect of oxidation states of Mn in Ca1−x Li x MnO3 on chemical-looping combustion reactions

We investigated the effect of the oxidation state of Mn in CaMnO3 perovskite particles to improve their oxygen transfer performance for chemical-looping combustion (CLC). Li was introduced in the Ca site of CaMnO3 to increase the Mn oxidation state. Ca1−x Li x MnO3 particles were synthesized by the solid-state method, and the amount of Li added ranged from 0 to 0.015 mol. The structure of the synthesized Ca1−x Li x MnO3 particles was examined using XRD, and all particles were confirmed to have a CaMnO3 perovskite structure. The shape and chemical properties of the prepared particles were characterized by using SEM and CH4-TPD. The binding energy and oxidation state of the different elements in the Ca1−x Li x MnO3 particles were measured by XPS. When Li was added, the oxidation state of Mn in Ca1−x Li x MnO3 was higher than that of Mn in CaMnO3. The oxygen transfer performance of the particles was determined by an isothermal H2-N2/air and CH4-CO2/air redox cycle at 850 °C, repeated ten times, using TGA. All particles showed an oxygen transfer capacity of about 8.0 to 9.0 wt%. Among them, Ca0.99Li0.01MnO3 particles had the best performance and the oxygen transfer capacity under H2-N2/air and CH4-CO2/air atmosphere was 8.47 and 8.75 wt%, respectively.

Perovskite-carbon composites synthesized through in situ autocombustion for the oxygen reduction reaction: the carbon effect

In this study, the authors synthesized perovskite-carbon composites by the In Situ AutoCombustion (ISAC) method. By physical-chemical characterization it was observed that nanoparticles of the LaMnO3±δ perovskite phase are well dispersed in the carbon matrix and are primarily located in the mesopores and small macropores of the Vulcan carbon. By electrochemical methods it was concluded that the oxygen reduction reaction (ORR) activity improvement of ISAC composites relative to perovskite/carbon composites prepared by mixing is due to the ISAC synthesis route and to the presence of carbon in the composites, which act by reducing the particle size of the perovskite, and decreasing their agglomeration degree. These result in the higher dispersion of perovskite particles and the ensuing increase of the number of catalytically active sites. Results of temperature programmed reduction reaction, X-ray photoelectron and electron energy loss spectroscopies suggest that perovskite particles in ISAC composites have lower oxygen stoichiometry compared to the unsupported LaMnO3 and are reduced by H2 at lower temperatures.

Thermochemical energy storage in strontium-doped calcium manganites for concentrating solar power applications

Thermochemical energy storage (TCES) using redox cycles of reducible perovskite oxides can potentially provide higher specific energy capacities and storage temperatures than molten-salt systems for large-scale energy storage in concentrating solar power (CSP) and other applications. Perovskites from earth abundant cations, such as CaMnO3, are needed for cost-effective solutions, but such materials must demonstrate favorable thermodynamics for high specific TCES (chemical+sensible) and favorable kinetics for heat-driven reduction and exothermic re-oxidation in the redox cycle. This paper explores the thermodynamics and kinetics of Ca1-xSrxMnO3-δ(x=0.05and0.1) particles for TCES redox cycles where the particles are heated and reduced in N2 (PO2≈10-4bar) to high temperatures TH up to 1000°C in a solid-particle solar receiver. Chemical and sensible energy stored in the reduced perovskite particles is released as needed to a power cycle via re-oxidation and cooling of the material. Variation of oxygen non-stoichiometry (δ) of Ca1-xSrxMnO3-δ with temperature and PO2 is measured via thermogravimetric analysis. Reaction enthalpy for reduction and re-oxidation is determined by fitting the variation of δ with temperature and PO2 to a two-reaction point defect model. The fits compare favorably to differential scanning calorimetry with overall reaction enthalpies varying significantly with δ. For CSP applications, limited time in the solar receiver for perovskite reduction requires fast kinetics to achieve high specific TCES. Once the material is characterized thermodynamically, kinetic measurements for particle reduction and re-oxidation are performed in a packed-bed reactor to assess rates of O2 release and uptake at various temperatures and PO2 with particles of diameter between250and425μm. Packed-bed experiments indicate that the low values of A-site Sr-doping stabilize the CaMnO3-δ structure and allow large δ at high temperatures and PO2≈10-4bar. In these time-limited redox cycling experiments between 500and900°C, mass-transfer limited kinetics allows the Ca0.95Sr0.05MnO3-δ to reach a specific TCES of 620kJkg−1, which is 78% of the equilibrium limit of 791kJkg−1. X-ray diffraction after 1000 redox cycles showed that the Ca1-xSrxMnO3-δ particles have excellent phase stability for the desired redox conditions.

Morphology control and phase transition of hexagonal sodium niobate particles

Abstract Hexagonal NaNbO 3 particles with an ilmenite structure and plate-like morphology were synthesized by a hydrothermal method. The morphological evolution of the solid products with the increasing mineralizer concentration was monitored via SEM during the hydrothermal reaction. By carefully controlling the mineralizer concentration, particles with a diameter of 10–60 µm and a thickness of 1–10 µm were obtained. The particles were transformed from the ilmenite structure into the perovskite structure during the thermal treatment at 600 °C. Their plate-like morphology was maintained with some cracking on the surface. The surface orientation of the perovskite particles was micro- and macroscopically characterized by EBSD and XRD analysis, respectively. The results indicate that thinner particles tend to be more oriented in the (00 l) crystal planes.

Tiny Particles with Big Impacts on Clean Future Energy

Tiny Particles with Big Impacts on Clean Future Energy

Phase transition of Fe2O3–NiO to NiFe2O4 in perovskite catalytic particles for enhanced methane chemical looping reforming-decomposition with CO2 conversion

This work introduced a perovskite catalytic particle of Fe2O3–NiO/La0.8Sr0.2FeO3 as an oxygen carrier and investigated its long-term activity and stability in a novel methane Chemical Looping Reforming-Decomposition (CLRD) process. Carbon dioxide (CO2) was injected for the oxidation of the reduced catalytic particle and its carbon deposit, resulting in the accelerated production of syngas. The catalytic particle showed over 97% of CH4 conversion over 60min and the reduced catalytic particle was partially re-oxidized by both O2 and CO2 with the conversion of CO2 into CO maintaining about 93% over 80min. The separate phases of Fe2O3/NiO were gradually merged to the single crystal phase of NiFe2O4 during the calcination of the two metal oxides and the continuous redox reaction cycle. The increased crystallinity can lead to the improvement of both activity and stability due to the enhanced oxygen-carrying capacity. The structure of the catalytic particle was well preserved and its activity has been stable in the long-term CLRD cycle with the combination of CO2 utilization.

Perovskite-Type La0.8Sr0. 2Co0. 8Fe0. 2O3 with Uniform Dispersion on Graphene As an Efficient Bi-Functional Li-O2 Battery Cathode

With the increasing threat from the energy demand, greenhouse effect and environmental pollution, searching for new clean and rechargeable energy to replace conventional fuel energy has been our research urgency.[1] In recent years, Li-ion technology has captured the potable electronics market, invaded the power tool equipment markets because of its low cost, long cycle life and good reversibility. However, the energy density of commercial lithium-ion batteries (theoretical value is 400 Wh kg-1) is far from meeting the high energy demands of large-scale electricity storage for renewable energy.[2] Lithium oxygen (Li-O2) batteries with a theoretical energy density of 11140 Whkg-1 have been thought to be the most attractive contender in the future power tool equipment markets. Nevertheless, recent studies have demonstrated that the insulated products Li2O2 or electrolyte decomposition products would passivate the cathode which could cause very high charge-discharge overpotential. Moreover, the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) also compromise the capacity and cycle life.[3, 4] Noble metals may possess the highest bi-functional (ORR and OER) catalytic activities, but the expensive prices prevent them from large-scale applications. Therefore, it is crucial to find an efficient bi-functional and no-precious metal cathod for Li-O2 batteries.[5] Our previous work have been demonstrated that perovskite oxides La0.6Sr0.4Co0.2Fe0.8O3 (LSCF6428) is an effective and costless bi-functional catalyst in Li-O2 batteries especially for OER to reduce the charge potential. As like as the oxygen cathod of many other researchers, our cathod is composed of Ketjen black EC-600JD (KB), polyvinylidene fluoride (PVDF) and the as-prepared perovskite oxides, but the perovskite and KB partikles can’t uniformly distribute on the current collector, which can damage the performance of batteries.[6, 7] Reduced graphene oxide (rGO) have been applid as electrocatalyst and cathod to enhance the activity for ORR while still struggle poor stability during OER process.[8] Herein a bi-functional cathode composed of perovskite oxidesLa0.8Sr0. 2Co0. 8Fe0. 2O3 (LSCF8282) and rGO have been prepared and employed in Li-O2batteries. As shown in Figure 1, the perovskite particles with about 50 nm can uniformly disperse on the rGO nanoplatelets. Moreover, the composite cathod have shown both efficient OER and ORR activities accordding to the cyclic voltammetry measurements. The detailed results and specific analysis will be exhibited in the presentation. Acknowledgements: The authors would like to thank Materials Characterization Center of Huazhong University of Science and Technology for samples characterization assistance.

Ammonium-iodide-salt additives induced photovoltaic performance enhancement in one-step solution process for perovskite solar cells

Unordered aggregation of perovskite particles on TiO2 mesoporous film surface is a common problem in one-step solution process for fabricating perovskite solar cells (PSCs). This phenomenon is harmful for homogeneous dispersion of perovskite in mesoporous TiO2 film and responsible for the low photovoltaic performance of corresponding perovskite solar cells at the same time. Delicate control of perovskite nucleation and growth is an effective route to solve this problem. In this work, we proposed a facile strategy to improve perovskite (CH3NH3PbI3) growth by adding C6H5CH2NH3I (BAI) or NH4I ionic compounds in perovskite precursor solution. We investigated perovskite crystal structure and morphology, optical and electrochemical properties of perovskite films or devices using different additives by XRD, SEM, UV–Vis, IPCE, and EIS. We found that these additives could decrease the grain size of perovskite crystal and diminish perovskite particle aggregation on TiO2 film surface. This effect is benefit for electron transfer on perovskite/TiO2 interface. Finally, perovskite solar cells using BAI or NH4I additives obtain the best solar-to-electricity conversion efficiency of 9.05% and 9.49%, respectively, which are much higher than that of the pristine one, 6.83%.

Measuring Thermochemical Energy Storage Capacity with Redox Cycles of Doped-CaMnO3

Our team has explored redox cycles of doped CaMnO3-δ between air and low O2 partial pressures (~10-4 bar) for high-temperature thermochemical energy storage (TCES) applications. In this study, we have explored both A-site and B-site doped compositions using earth-abundant cations to identify perovskites for cost-effective TCES in concentrated solar and other high-temperature, thermal storage applications. Reduction of doped CaMnO3-δ above 800 °C in the low P O2 requires some amount of dopant to avoid irreversible decomposition of the perovskite structure observed for reduction of undoped CaMnO3-δ [1]. This study shows that small amounts (5%) of A-site or B-site dopant can stabilize the CaMnO3-δ perovskite structure during reduction at temperatures up to 1100 °C and P O2 = 10-4 bar. For selected, stable doped CaMnO3-δ compositions, total specific TCES (Δh tot) was defined by the sum of specific sensible energy (Δh sens) and chemical energy (Δh chem) captured during heating and reduction from air at a cool temperature (T C fixed at 500 °C in this study) to low P O2 at varying high temperatures ( T H). B-site doping with 5% Cr and A-site doping with 5% Sr provided thermodynamic limits of Δh tot over 720 kJ kg-1 and 790 kJ kg-1 respectively for T H = 1000 °C. These materials were also tested kientically to assess the rates at which energy storage is captured during reduction and released during oxidation as relevant for concentrated solar energy storage applications. The results indicate that the doped CaMnO3-δ and in particular A-site doped Ca0.95Sr0.05MnO3-δ have promise as a TCES storage media with Δh chem providing just under half of the total energy stored during the combined heating and reduction. For the perovskite redox cycles, the heat of oxide reduction -ΔH O can vary with non-stoichometry δ [2]. To find the integrated Δh chem, the functional dependence of ΔH O with δ must be detemined. Two methods have been undertaken to explore this functional dependence: 1) combined TGA-DSC calorimetry measurements with incremental changes in δ, and 2) point-defect model fitting to equilibrium δ vs. P O2 data from TGA measurements [3,4]. The DSC measurements showed that the magnitude of ΔH O decreases to a near constant value for δ > 0.1 as illustrated for Ca0.95Sr0.05MnO3-δ in Figure 1. Similar trends were observed for the other perovskite compositions. The alternative method for finding ΔH O as a function of δ by fitting the equilibrium δ vs. P O2 involved modeling the perovskite reduction with two reversible point-defect reactions -- oxide-ion vacancy formation and Mn cation disproportionation from 4+ to 3+ and 5+ states [4]. The model fits originally assumed that these two reactions had enthalpies independent of δ but the contribution of the disproportionation reaction increased with δ thereby causing the combined ΔH O to have a minor dependence on δ as also shown in Figure 1. The point defect modeling did not show the same trends for ΔH O vs. δ but provided very similar values at high δ > 0.1. The integration of ΔH O over a change in δ (i.e. Δδ as in Table 1) provides a basis for calculating the integrated Δh chem as a function of T H. Integrated Δh chem values for CaCr0.05Mn0.95O3-δ, Ca0.95Sr0.05MnO3-δ, and Ca0.9Sr0.1MnO3-δ are shown in Table 1 along with the total energy stored which includes Δh sens derived from integration of CP with respect to T over the redox cycle heating. The higher Δh chem and associated Δh tot for Ca0.95Sr0.05MnO3-δ stems from its increase reducibility without a loss in heat of reaction and makes it a more promising material for TCES applications in these temperature ranges.For thermal storage application, kinetic rates of TCES capture are important, particularly for concentrated solar applications where solar receiver residence times are limited. To explore kinetics, reduction and oxidation rates of porous perovskite particle beds were measured for fitting thermodynamically consistent kinetic models to the observed rates. Kinetic testing and model fitting for the Ca0.95Sr0.05MnO3-δ indicates that it achieves approximately 80% of its Δh chem thermodynamic limit in 60 s exposure of low P O2 gas for reduction at T H = 900 °C. On the other hand, at the same temperature reoxidation occurs rapidly and releases over 90% of the Δh chem limit in 30 s. The thermodynamic consistent model involving surface kinetics and ionic bulk diffusion in the perovskite particles for Ca0.95Sr0.05MnO3-δ and for CaCr0.05Mn0.95O3-δ provide a basis for designing reactors for redox cycles to be used in TCES for concentrated solar and other potential thermal energy storage applications.

Enhanced photoelectrical performance of dye-sensitized solar cells with double-layer TiO2 on perovskite SrTiO3 substrate

In this research, perovskite SrTiO3 particles are synthesized by a hydrothermal method, and TiO2 with a double-layer structure is grown on the SrTiO3 surface by a hydrolysis–condensation process. Structural characterizations reveal that TiO2 comprises of two phases: anatase film at the bottom and single-crystal rutile nanorods grown along the [110] direction on top. The TiO2–SrTiO3 composite film is investigated as photoanode material for dye-sensitized solar cells. In comparison with pure TiO2 and SrTiO3, the composite photoanode shows a much better performance in photoelectric conversion efficiency (1.35 %), which is about 2 and 100 times as efficient as pure TiO2 and SrTiO3, respectively. This indicates that the composite structure can facilitate charge carrier transfer and reduce electron–hole recombination to enhance photoelectrical properties of TiO2-based photoanode materials.

Photochemically Driven Modulated Charge Transfer at Local Contacts between CH3NH3PbI3 and Carboxylated Multiwalled Carbon Nanotubes

Spectral dependent charge separation was investigated by modulated surface photovoltage (SPV) on layer systems with local contacts between CH3NH3PbI3 and PEDOT:PSS mixed with carboxylated multiwalled carbon nanotubes (MWCNT-COOH). In-phase SPV signals changed the sign with increasing amount of MWCNT-COOH in the PEDOT:PSS whereas the spectra could be approximated by a superposition of the spectra obtained for pure PEDOT:PSS and for PEDOT:PSS with 1.6 wt % of MWCNT-COOH. This was not the case for the control sample with pristine MWCNT. For a complex of a single-walled CNT-COOH (SWCNT-COOH) with a perovskite particle, density functional theory calculations showed an electron transfer to the perovskite which was not the case for a pristine SWCNT. Therefore, the transfer of electrons from MWCNT-COOH into illuminated CH3NH3PbI3 dominates fast separation of photogenerated charge carriers at local contacts with MWCNT-COOH.

Effect of excess PbBr2 on photoluminescence spectra of CH3NH3PbBr3 perovskite particles at room temperature

The organic-inorganic halide perovskites have promising applications in light-emitting devices besides solar cells. We here prepare CH3NH3PbBr3 perovskite particles on SiO2 substrates and find that the photoluminescence (PL) spectrum of the particles at room temperature has two peaks, locating at 529 and 549 nm, respectively, much different from that of the corresponding films prepared on the oxygen plasma-cleaned SiO2 substrates, which has a single peak. The double peaks have different temperature-dependence behaviors. By the x-ray diffraction and energy dispersive x-ray spectroscopy analyses, excess PbBr2 is detected inside the particles. We deduce that such excess PbBr2 has introduced shallow level defects. It is concluded that band-to-band recombination and these defects result in the double-peaked feature of the PL spectra of CH3NH3PbBr3 particles at room temperature.

Dynamic Growth of Pinhole-Free Conformal CH3NH3PbI3 Film for Perovskite Solar Cells.

Two-step dipping is one of the popular low temperature solution methods to prepare organic-inorganic halide perovskite (CH3NH3PbI3) films for solar cells. However, pinholes in perovskite films fabricated by the static growth method (SGM) result in low power conversion efficiency (PCE) in the resulting solar cells. In this work, the static dipping process is changed into a dynamic dipping process by controlled stirring PbI2 substrates in CH3NH3I isopropanol solution. The dynamic growth method (DGM) produces more nuclei and decreases the pinholes during the nucleation and growth of perovskite crystals. The compact perovskite films with free pinholes are obtained by DGM, which present that the big perovskite particles with a size of 350 nm are surrounded by small perovskite particles with a size of 50 nm. The surface coverage of the perovskite film is up to nearly 100%. Such high quality perovskite film not only eliminated pinholes, resulting in reduced charge recombination of the solar cells, but also improves the light harvesting efficiency. As a result, the PCE of the perovskite solar cells is increased from 11% for SGM to 13% for DGM.

共沉淀法制备LaFe<sub>X</sub>Co<sub>1-X</sub>O<sub>3</sub>钙钛矿的研究

以La(NO3)3ž6H2O、Co(NO3)3ž6H2O和Fe(NO3)3ž9H2O为原料，用共沉淀法对制备LaFexCo1−xO3 (x = 0.2, 0.5, 0.8)钙钛矿进行研究。热重–差示量热分析(TG-DSC)和X射线衍射(XRD)分析表明，合成LaFexCo1−xO3钙钛矿过程有四段失重，分别在110℃之前、150℃~220℃、300℃~500℃和700℃~780℃；经过700℃~800℃煅烧后有钙钛矿形成，之后随煅烧温度提高，钙钛矿生成量逐渐增加，晶粒尺寸也缓慢增加，煅烧温度为1000℃时获得钙钛矿的量最多，但是与800℃和900℃煅烧后形成钙钛矿相比，其晶粒尺寸增加较多；随着Fe取代Co的量增加，形成钙钛矿尺寸晶粒尺寸逐渐降低。 Preparation of LaFexCo1−xO3 (x = 0.2, 0.5, 0.8) perovskite by coprecipitation using La(NO3)3ž6H2O, Co(NO3)3ž6H2O和Fe(NO3)3ž9H2O and Fe(NO3)3ž9H2O as raw materials was researched. The phenomena observed were characterized using Thermogravimetry-Differential Scanning Calorimetric (TG-DSC) and X- ray diffraction (XRD). Results showed that process of preparing LaFexCo1−xO3 perovskite appeared four period of weight loss at less than 110˚C, 150˚C - 220˚C, 300˚C - 500˚C and 700˚C - 780˚C, respectively. The sample calcined at 700˚C - 800˚C has already formed perovskite, then amount of forming perovsktie and the grain size of perovskite increase gradually with the calcination temperature. When calcination temperature is at 1000˚C, the most amount of perovskite is gained, but the grain size increases more than that of perovskite calcined at 800˚C and 900˚C. With the increase of substitute Fe for Co, perovskite particle size is gradually reduced.

Preparation and characterization of methylammonium tin iodide layers as photovoltaic absorbers

The preparation of absorber layers composed of methylammonium tin iodide (CH3NH3SnI3) in a two-step process was investigated. This material is designed as a less toxic alternative to CH3NH3PbI3 which is commonly used as active material in perovskite solar cells. Tin(II) iodide (SnI2) layers prepared by physical vapor deposition were converted to CH3NH3SnI3 by reaction with a spin-coated solution of methylammonium iodide (MAI). The perovskite particles formed in this process were over 200 nm in size and reached full surface coverage. A band gap of 1.23 eV was determined and the material, thus, absorbs over a broad part of the solar spectrum, broader even than CH3NH3PbI3. The chemical composition and solid state structure of the prepared films were analyzed by X-ray photoelectron spectroscopy and X-ray diffraction, respectively. The films turned out to be remarkably stable, another key prerequisite for applications as absorber layers in perovskite solar cells.