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Showing papers on "Perovskite (structure) published in 2013"


Journal ArticleDOI
18 Jul 2013-Nature
TL;DR: A sequential deposition method for the formation of the perovskite pigment within the porous metal oxide film that greatly increases the reproducibility of their performance and allows the fabrication of solid-state mesoscopic solar cells with unprecedented power conversion efficiencies and high stability.
Abstract: Following pioneering work, solution-processable organic-inorganic hybrid perovskites-such as CH3NH3PbX3 (X = Cl, Br, I)-have attracted attention as light-harvesting materials for mesoscopic solar cells. So far, the perovskite pigment has been deposited in a single step onto mesoporous metal oxide films using a mixture of PbX2 and CH3NH3X in a common solvent. However, the uncontrolled precipitation of the perovskite produces large morphological variations, resulting in a wide spread of photovoltaic performance in the resulting devices, which hampers the prospects for practical applications. Here we describe a sequential deposition method for the formation of the perovskite pigment within the porous metal oxide film. PbI2 is first introduced from solution into a nanoporous titanium dioxide film and subsequently transformed into the perovskite by exposing it to a solution of CH3NH3I. We find that the conversion occurs within the nanoporous host as soon as the two components come into contact, permitting much better control over the perovskite morphology than is possible with the previously employed route. Using this technique for the fabrication of solid-state mesoscopic solar cells greatly increases the reproducibility of their performance and allows us to achieve a power conversion efficiency of approximately 15 per cent (measured under standard AM1.5G test conditions on solar zenith angle, solar light intensity and cell temperature). This two-step method should provide new opportunities for the fabrication of solution-processed photovoltaic cells with unprecedented power conversion efficiencies and high stability equal to or even greater than those of today's best thin-film photovoltaic devices.

8,427 citations


Journal ArticleDOI
18 Oct 2013-Science
TL;DR: In this article, transient absorption and photoluminescence-quenching measurements were performed to determine the electron-hole diffusion lengths, diffusion constants, and lifetimes in mixed halide and triiodide perovskite absorbers.
Abstract: Organic-inorganic perovskites have shown promise as high-performance absorbers in solar cells, first as a coating on a mesoporous metal oxide scaffold and more recently as a solid layer in planar heterojunction architectures. Here, we report transient absorption and photoluminescence-quenching measurements to determine the electron-hole diffusion lengths, diffusion constants, and lifetimes in mixed halide (CH3NH3PbI(3-x)Cl(x)) and triiodide (CH3NH3PbI3) perovskite absorbers. We found that the diffusion lengths are greater than 1 micrometer in the mixed halide perovskite, which is an order of magnitude greater than the absorption depth. In contrast, the triiodide absorber has electron-hole diffusion lengths of ~100 nanometers. These results justify the high efficiency of planar heterojunction perovskite solar cells and identify a critical parameter to optimize for future perovskite absorber development.

8,199 citations


Journal ArticleDOI
TL;DR: It is found that the chemical and physical properties of these materials strongly depend on the preparation method, and the properties of the title hybrid materials with those of the "all-inorganic" CsSnI3 and CsPbI3 prepared using identical synthetic methods.
Abstract: A broad organic–inorganic series of hybrid metal iodide perovskites with the general formulation AMI3, where A is the methylammonium (CH3NH3+) or formamidinium (HC(NH2)2+) cation and M is Sn (1 and 2) or Pb (3 and 4) are reported. The compounds have been prepared through a variety of synthetic approaches, and the nature of the resulting materials is discussed in terms of their thermal stability and optical and electronic properties. We find that the chemical and physical properties of these materials strongly depend on the preparation method. Single crystal X-ray diffraction analysis of 1–4 classifies the compounds in the perovskite structural family. Structural phase transitions were observed and investigated by temperature-dependent single crystal X-ray diffraction in the 100–400 K range. The charge transport properties of the materials are discussed in conjunction with diffuse reflectance studies in the mid-IR region that display characteristic absorption features. Temperature-dependent studies show a ...

4,372 citations


Journal ArticleDOI
TL;DR: In this paper, a layered sandwich-type architecture is proposed for next-generation dye-sensitized solar cells, which consists of a bicontinuous three-dimensional nanocomposite of mesoporous (mp)-TiO2,w ith CH 3NH3PbII3 perovskite as light harvester, as well as a polymeric hole conductor.
Abstract: Inorganic‐organic hybrid structures have become innovative alternatives for next-generation dye-sensitized solar cells, because they combine the advantages of both systems. Here, we introduce a layered sandwich-type architecture, the core of which comprises a bicontinuous three-dimensional nanocomposite of mesoporous (mp)-TiO2 ,w ith CH 3NH3PbI3 perovskite as light harvester, as well as a polymeric hole conductor. This platform creates new opportunities for the development of low-cost, solution-processed, high-efficiency solar cells. The use of a polymeric hole conductor, especially poly-triarylamine, substantially improves the open-circuit voltage V oc and fill factor of the cells. Solar cells based on these inorganic‐organic hybrids exhibit a short-circuit current density Jsc of 16.5 mA cm 22 , Voc of 0.997 V and fill factor of 0.727, yielding a power conversion efficiency of 12.0% under standard AM 1.5 conditions.

2,461 citations


Journal ArticleDOI
TL;DR: In this paper, a detailed description of the preparation, structural characterisation and physical characteristics of hybrid organic-inorganic perovskite (CH3NH3)PbI3 is presented.
Abstract: The hybrid organic–inorganic perovskite (CH3NH3)PbI3 may find application in next generation solid-state sensitised solar cells. Although this material and related perovskites were discovered many decades ago, questions remain concerning their diverse structural chemistry and unusual properties. The article presents a review of previous work and provides a detailed description of the preparation, structural characterisation and physical characteristics of (CH3NH3)PbI3. The phase changes exhibited by (CH3NH3)PbI3 have been probed using variable temperature powder and single crystal X-ray diffraction, combined with differential scanning calorimetry, thermogravimetric analysis and phase contrast transmission electron microscopy. The optical band gap for (CH3NH3)PbI3 determined by UV-Visible spectroscopy was compared to values obtained from density-of-state simulation of the electronic band structure.

2,132 citations


Journal ArticleDOI
TL;DR: It is demonstrated that a single thin film of the low-temperature solution-processed organometal trihalide perovskite absorber CH3NH3PbI3-xClx, sandwiched between organic contacts can exhibit devices with power-conversion efficiency of up to 10% on glass substrates and over 6% on flexible polymer substrates.
Abstract: Organometal trihalide perovskite solar cells offer the promise of a low-cost easily manufacturable solar technology, compatible with large-scale low-temperature solution processing. Within 1 year of development, solar-to-electric power-conversion efficiencies have risen to over 15%, and further imminent improvements are expected. Here we show that this technology can be successfully made compatible with electron acceptor and donor materials generally used in organic photovoltaics. We demonstrate that a single thin film of the low-temperature solution-processed organometal trihalide perovskite absorber CH3NH3PbI3-xClx, sandwiched between organic contacts can exhibit devices with power-conversion efficiency of up to 10% on glass substrates and over 6% on flexible polymer substrates. This work represents an important step forward, as it removes most barriers to adoption of the perovskite technology by the organic photovoltaic community, and can thus utilize the extensive existing knowledge of hybrid interfaces for further device improvements and flexible processing platforms.

1,539 citations


Journal ArticleDOI
TL;DR: In this paper, the bulk absorber layer of CH3NH3PbI3−xClx perovskite solar cells was reduced from 500 to <150 °C and achieved power conversion efficiency up to 12.3%.
Abstract: We have reduced the processing temperature of the bulk absorber layer in CH3NH3PbI3−xClx perovskite solar cells from 500 to <150 °C and achieved power conversion efficiencies up to 12.3%. Remarkably, we find that devices with planar thin-film architecture, where the ambipolar perovskite transports both holes and electrons, convert the absorbed photons into collected charge with close to 100% efficiency.

1,524 citations


Journal ArticleDOI
TL;DR: All-solid-state donor/acceptor planar-heterojunction (PHJ) hybrid solar cells are constructed and their excellent performance measured.
Abstract: All-solid-state donor/acceptor planar-heterojunction (PHJ) hybrid solar cells are constructed and their excellent performance measured. The deposition of a thin C60 fullerene or fullerene-derivative (acceptor) layer in vacuum on a CH3 NH3 PbI3 perovskite (donor) layer creates a hybrid PHJ that displays the photovoltaic effect. Such heterojunctions are shown to be suitable for the development of newly structured, hybrid, efficient solar cells.

1,327 citations


Journal ArticleDOI
TL;DR: In this article, the perovskite CH3NH3PbX3 (X = Cl, Br, or I) sensitizer made a breakthrough in solid-state mescoscopic solar cells, where the first record efficiency of around 10% was reported in 2012 using submicrometer-thick TiO2 film sensitized with CH 3NH3pbI3. A rapid increase in efficiency approaching 14% followed shortly.
Abstract: Recently, perovskite CH3NH3PbI3 sensitizer has attracted great attention due to its superb light-harvesting characteristics. Organometallic or organic materials were mostly used as sensitizers for solid-state dye-sensitized solar cells at early stages. Inorganic nanocrystals have lately received attention as light harvesters due to their high light-absorbing properties. Metal chalcogenides have been investigated with solid-state dye-sensitized solar cells; however, the best power conversion efficiency was reported to be around 6%. CH3NH3PbX3 (X = Cl, Br, or I) perovskite sensitizer made a breakthrough in solid-state mescoscopic solar cells, where the first record efficiency of around 10% was reported in 2012 using submicrometer-thick TiO2 film sensitized with CH3NH3PbI3. A rapid increase in efficiency approaching 14% followed shortly. In this Perspective, recent progress in perovskite-sensitized solid-state mesoscopic solar cells is reviewed. On the basis of the recent achievements, a power conversion eff...

1,275 citations


Journal ArticleDOI
TL;DR: The perovskite compound CsPbBr3 as mentioned in this paper is a direct band gap semiconductor which meets most of the requirements for successful detection of X and γ-ray radiation, such as high attenuation, high resistivity, and significant photoconductivity response, with detector resolution comparable to that of commercial, state-of-the-art materials.
Abstract: The synthesis, crystal growth, and structural and optoelectronic characterization has been carried out for the perovskite compound CsPbBr3. This compound is a direct band gap semiconductor which meets most of the requirements for successful detection of X- and γ-ray radiation, such as high attenuation, high resistivity, and significant photoconductivity response, with detector resolution comparable to that of commercial, state-of-the-art materials. A structural phase transition which occurs during crystal growth at higher temperature does not seem to affect its crystal quality. Its μτ product for both hole and electron carriers is approximately equal. The μτ product for electrons is comparable to cadmium zinc telluride (CZT) and that for holes is 10 times higher than CZT.

1,143 citations


Journal ArticleDOI
28 Nov 2013-Nature
TL;DR: The ability of KBNNO to absorb three to six times more solar energy than the current ferroElectric materials suggests a route to viable ferroelectric semiconductor-based cells for solar energy conversion and other applications.
Abstract: Most known ferroelectric photovoltaic materials have very wide electronic bandgaps (that is, they absorb only high-energy photons) but here a family of perovskite oxides is described that have tunable bandgaps, allowing their use across the whole visible-light spectrum. The spontaneous electrical polarization that characterizes a ferroelectric material is attractive for solar-cell applications as the positive and negative charges generated by light absorption have a natural tendency to separate, making them easier to harvest efficiently. Unfortunately most known ferroelectrics have wide electronic bandgaps — that is they absorb only higher energy photons that make up a small fraction of the solar spectrum. Ilya Grinberg and colleagues now show that a classic ferroelectric can be chemically engineered to tune the bandgap over a broad range, achieving strong absorption and photocurrent generation across the solar spectrum. Ferroelectrics have recently attracted attention as a candidate class of materials for use in photovoltaic devices, and for the coupling of light absorption with other functional properties1,2,3,4,5,6,7. In these materials, the strong inversion symmetry breaking that is due to spontaneous electric polarization promotes the desirable separation of photo-excited carriers and allows voltages higher than the bandgap, which may enable efficiencies beyond the maximum possible in a conventional p–n junction solar cell2,6,8,9,10. Ferroelectric oxides are also stable in a wide range of mechanical, chemical and thermal conditions and can be fabricated using low-cost methods such as sol–gel thin-film deposition and sputtering3,5. Recent work3,5,11 has shown how a decrease in ferroelectric layer thickness and judicious engineering of domain structures and ferroelectric–electrode interfaces can greatly increase the current harvested from ferroelectric absorber materials, increasing the power conversion efficiency from about 10−4 to about 0.5 per cent. Further improvements in photovoltaic efficiency have been inhibited by the wide bandgaps (2.7–4 electronvolts) of ferroelectric oxides, which allow the use of only 8–20 per cent of the solar spectrum. Here we describe a family of single-phase solid oxide solutions made from low-cost and non-toxic elements using conventional solid-state methods: [KNbO3]1 − x[BaNi1/2Nb1/2O3 − δ]x (KBNNO). These oxides exhibit both ferroelectricity and a wide variation of direct bandgaps in the range 1.1–3.8 electronvolts. In particular, the x = 0.1 composition is polar at room temperature, has a direct bandgap of 1.39 electronvolts and has a photocurrent density approximately 50 times larger than that of the classic ferroelectric (Pb,La)(Zr,Ti)O3 material. The ability of KBNNO to absorb three to six times more solar energy than the current ferroelectric materials suggests a route to viable ferroelectric semiconductor-based cells for solar energy conversion and other applications.

Journal ArticleDOI
TL;DR: A continuous drop of voltage with increasing nanorod length correlated with charge generation efficiency rather than recombination kinetics with impedance spectroscopic characterization displaying similar recombination regardless of the nanorods length.
Abstract: We report a highly efficient solar cell based on a submicrometer (∼0.6 μm) rutile TiO2 nanorod sensitized with CH3NH3PbI3 perovskite nanodots. Rutile nanorods were grown hydrothermally and their lengths were varied through the control of the reaction time. Infiltration of spiro-MeOTAD hole transport material into the perovskite-sensitized nanorod films demonstrated photocurrent density of 15.6 mA/cm2, voltage of 955 mV, and fill factor of 0.63, leading to a power conversion efficiency (PCE) of 9.4% under the simulated AM 1.5G one sun illumination. Photovoltaic performance was significantly dependent on the length of the nanorods, where both photocurrent and voltage decreased with increasing nanorod lengths. A continuous drop of voltage with increasing nanorod length correlated with charge generation efficiency rather than recombination kinetics with impedance spectroscopic characterization displaying similar recombination regardless of the nanorod length.

Journal ArticleDOI
TL;DR: A fingerprint of the charge accumulation in high density of states of the perovskite absorber material has been observed at the capacitance of the samples, indicating that it constitutes a new kind of photovoltaic device, differentiated from sensitized solar cells, which will require its own methods of study, characterization and optimization.
Abstract: Photovoltaic conversion requires two successive steps: accumulation of a photogenerated charge and charge separation. Determination of how and where charge accumulation is attained and how this accumulation can be identified is mandatory for understanding the performance of a photovoltaic device and for its further optimization. Here we analyse the mechanism of carrier accumulation in lead halide perovskite, CH3NH3PbI3, thin-absorber solar cells by means of impedance spectroscopy. A fingerprint of the charge accumulation in high density of states of the perovskite absorber material has been observed at the capacitance of the samples. This is, as far as we know, the first observation of charge accumulation in light-absorbing material for nanostructured solar cells, indicating that it constitutes a new kind of photovoltaic device, differentiated from sensitized solar cells, which will require its own methods of study, characterization and optimization.

Journal ArticleDOI
TL;DR: In this paper, the structural properties of iodide/chloride mixed-halide perovskites and correlating them with their photovoltaic performances were investigated, and they found that, independent of the components ratio in the precursor solution, Cl incorporation in an iodide-based structure, is possible only at relatively low concentration levels (below 3-4%).
Abstract: Hybrid halide perovskites represent one of the most promising solutions toward the fabrication of all solid nanostructured solar cells, with improved efficiency and long-term stability. This article aims at investigating the structural properties of iodide/chloride mixed-halide perovskites and correlating them with their photovoltaic performances. We found out that, independent of the components ratio in the precursor solution, Cl incorporation in an iodide-based structure, is possible only at relatively low concentration levels (below 3–4%). However, even if the material band gap remains substantially unchanged, the Cl doping dramatically improves the charge transport within the perovskite layer, explaining the outstanding performances of meso-superstructured solar cells based on this material.

Journal ArticleDOI
TL;DR: The first theoretical estimation of effective masses of photocarriers in CH3NH3PbI3 is reported, consistent with the long-range ambipolar transport property and with the larger diffusion constant for electrons compared with that for holes in the perovskite, which enable efficient photovoltaic conversion.
Abstract: Methylammonium lead iodide perovskite (CH3NH3PbI3) plays an important role in light absorption and carrier transport in efficient organic-inorganic perovskite solar cells. In this Letter, we report the first theoretical estimation of effective masses of photocarriers in CH3NH3PbI3. Effective masses of photogenerated electrons and holes were estimated to be me* = 0.23m0 and mh* = 0.29m0, respectively, including spin-orbit coupling effects. This result is consistent with the long-range ambipolar transport property and with the larger diffusion constant for electrons compared with that for holes in the perovskite, which enable efficient photovoltaic conversion.

Journal ArticleDOI
TL;DR: The C60SAM functionalization of mesoporous TiO2 is used to achieve an 11.7% perovskite-sensitized solar cell using Spiro-OMeTAD as a transparent hole transporter and this strategy allows a reduction of energy loss, while still employing a "mesoporous electron acceptor".
Abstract: A plethora of solution-processed materials have been developed for solar cell applications. Hybrid solar cells based on light absorbing semiconducting polymers infiltrated into mesoporous TiO2 are an interesting concept, but generating charge at the polymer–metal oxide heterojunction is challenging. Metal–organic perovskite absorbers have recently shown remarkable efficiencies but currently lack the range of color tunability of organics. Here, we have combined a fullerene self-assembled monolayer (C60SAM) functionalized mesoporous titania, a perovskite absorber (CH3NH3PbI3–xClx), and a light absorbing polymer hole-conductor, P3HT, to realize a 6.7% efficient hybrid solar cell. We find that photoexcitations in both the perovskite and the polymer undergo very efficient electron transfer to the C60SAM. The C60SAM acts as an electron acceptor but inhibits further electron transfer into the TiO2 mesostructure due to energy level misalignment and poor electronic coupling. Thermalized electrons from the C60SAM a...

Journal ArticleDOI
TL;DR: The performance of perovskite solar cells recently exceeded 15% solar-to-electricity conversion efficiency for small-area devices as mentioned in this paper, and the fundamental properties of the active absorber layers, hybrid organic-inorganic perovsites formed from mixing metal and organic halides, are largely unknown.
Abstract: The performance of perovskite solar cells recently exceeded 15% solar-to-electricity conversion efficiency for small-area devices. The fundamental properties of the active absorber layers, hybrid organic-inorganic perovskites formed from mixing metal and organic halides [e.g., (NH4)PbI3 and (CH3NH3)PbI3], are largely unknown. The materials are semiconductors with direct band gaps at the boundary of the first Brillouin zone. The calculated dielectric constants and band gaps show an orientation dependence, with a low barrier for rotation of the organic cations. Due to the electric dipole of the methylammonium cation, a photoferroic effect may be accessible, which could enhance carrier collection.

Journal ArticleDOI
TL;DR: A ZNO compact layer formed by electrodeposition and ZnO nanorods grown by chemical bath deposition allow the processing of low-temperature, solution based and flexible solid state perovskite CH3NH3PbI3 solar cells.

Journal ArticleDOI
TL;DR: This work demonstrates photocurrent and efficiency enhancement in meso-superstructured organometal halide perovskite solar cells incorporating core-shell Au@SiO2 nanoparticles (NPs) delivering a device efficiency of up to 11.4%.
Abstract: Recently, inorganic and hybrid light absorbers such as quantum dots and organometal halide perovskites have been studied and applied in fabricating thin-film photovoltaic devices because of their low-cost and potential for high efficiency. Further boosting the performance of solution processed thin-film solar cells without detrimentally increasing the complexity of the device architecture is critically important for commercialization. Here, we demonstrate photocurrent and efficiency enhancement in meso-superstructured organometal halide perovskite solar cells incorporating core-shell Au@SiO2 nanoparticles (NPs) delivering a device efficiency of up to 11.4%. We attribute the origin of enhanced photocurrent to a previously unobserved and unexpected mechanism of reduced exciton binding energy with the incorporation of the metal nanoparticles, rather than enhanced light absorption. Our findings represent a new aspect and lever for the application of metal nanoparticles in photovoltaics and could lead to facile tuning of exciton binding energies in perovskite semiconductors.

Journal ArticleDOI
TL;DR: Judicious selection of the perovskite lead halide-based absorber, matching organic hole conductor, and contacts, a cell with a ∼ 1.3 V open circuit voltage was made and provides a general guideline for additional improvement of cell performance.
Abstract: Mesoscopic solar cells, based on solution-processed organic-inorganic perovskite absorbers, are a promising avenue for converting solar to electrical energy. We used solution-processed organic-inorganic lead halide perovskite absorbers, in conjunction with organic hole conductors, to form high voltage solar cells. There is a dire need for low-cost cells of this type, to drive electrochemical reactions or as the high photon energy cell in a system with spectral splitting. These perovskite materials, although spin-coated from solution, form highly crystalline materials. Their simple synthesis, along with high chemical versatility, allows tuning their electronic and optical properties. By judicious selection of the perovskite lead halide-based absorber, matching organic hole conductor, and contacts, a cell with a ∼ 1.3 V open circuit voltage was made. While further study is needed, this achievement provides a general guideline for additional improvement of cell performance.

Journal ArticleDOI
TL;DR: It is shown that the nature of the HTM is essential for charge recombination and elucidates that finding an optimal HTM for the perovskite solar cell includes controlling the perOVskite/HTM interaction.
Abstract: We report on perovskite (CH3NH3)PbI3-sensitized solid-state solar cells using spiro-OMeTAD, poly(3-hexylthiophene-2,5-diyl) (P3HT) and 4-(diethylamino)benzaldehyde diphenylhydrazone (DEH) as hole transport materials (HTMs) with a light to electricity power conversion efficiency of 8.5%, 4.5%, and 1.6%, respectively, under AM 1.5G illumination of 1000 W/m(2) intensity. Photoinduced absorption spectroscopy (PIA) shows that hole transfer occurs from the (CH3NH3)PbI3 to HTMs after excitation of (CH3NH3)PbI3. The electron lifetime (τe) in these devices are in the order Spiro-OMeTAD > P3HT > DEH, while the charge transport time (ttr) is rather similar. The difference in τe can therefore explain the lower efficiency of the devices based on P3HT and DEH. This report shows that the nature of the HTM is essential for charge recombination and elucidates that finding an optimal HTM for the perovskite solar cell includes controlling the perovskite/HTM interaction. Design routes for new HTMs are suggested.

Journal ArticleDOI
TL;DR: A facile, effective, and scalable strategy for preparing perovskite-based porous La0.75Sr0.25MnO3 nanotubes (PNT-LSM) by combining the electrospinning technique with a heating method is proposed and realized.
Abstract: Rechargeable lithium–oxygen (Li-O2) batteries have recently attracted great attention because they can theoretically store 5–10 times more energy than current lithium-ion batteries, which is essential for clean energy storage, electric vehicles, and other high-energy applications. However, to use Li-O2 batteries for practical applications, numerous scientific and technical challenges need to be surmounted. 8] In response, intensive research efforts have been made to address the challenges by incorporating metal oxides, metal nitrides, metal nanoparticles, 21] and organometallic compounds 22] as electrocatalysts in the O2 electrode. Although significant improvements in the oxygen-reductionreaction (ORR) and/or oxygen-evolution-reaction (OER) overpotentials have been achieved, there is still a demand for highly efficient electrocatalysts to further enhance the specific capacity, rate capability, and cyclic life especially at a high capacity. On the other hand, most of the catalyst performances reported thus far are tested using carbonate-based or mixed ether-carbonate-based electrolytes, which have now been shown to be not inert to the superoxide radical (O2C ) and thus are inevitably decomposed upon cell discharge/ charge. For example, Luntz and co-workers demonstrate that, when carbonate-based electrolytes are employed for LiO2 cells, the main role of the Au, Pt, and MnO2 catalysts is to catalyze the decomposition of the electrolytes. In this context, the development of OER and ORR electrocatalysts in a relatively stable electrolyte is thus of importance to realize a reversible Li-O2 battery. Compared to carbonate, ether-based electrolytes have been reported to be more suitable for Li-O2 batteries because the desired lithium peroxide is the dominant product. 29] However, there are not many reports on electrocatalysts for Li-O2 batteries with ether-based electrolytes. 10, 30, 33] Perovskite oxides have a high electronic/ionic conductivity and catalytic activity and thus could be a promising candidate as electrocatalyst for Li-O2 batteries. [33–35] Herein, we firstly propose and realize a facile, effective, and scalable strategy for preparing perovskite-based porous La0.75Sr0.25MnO3 nanotubes (PNT-LSM) by combining the electrospinning technique with a heating method. Figure 1

Journal ArticleDOI
TL;DR: A smaller size mismatch between the host and dopant cations and a chemically expanded lattice were found to reduce the segregation level of the dopant and to enable more stable cathode surfaces to tailor the cathode surface compositions for high-performance SOFCs.
Abstract: Cation segregation on perovskite oxide surfaces affects vastly the oxygen reduction activity and stability of solid oxide fuel cell (SOFC) cathodes. A unified theory that explains the physical origins of this phenomenon is therefore needed for designing cathode materials with optimal surface chemistry. We quantitatively assessed the elastic and electrostatic interactions of the dopant with the surrounding lattice as the key driving forces for segregation on model perovskite compounds, LnMnO3 (host cation Ln = La, Sm). Our approach combines surface chemical analysis with X-ray photoelectron and Auger electron spectroscopy on model dense thin films and computational analysis with density functional theory (DFT) calculations and analytical models. Elastic energy differences were systematically induced in the system by varying the radius of the selected dopants (Ca, Sr, Ba) with respect to the host cations (La, Sm) while retaining the same charge state. Electrostatic energy differences were introduced by varying the distribution of charged oxygen and cation vacancies in our models. Varying the oxygen chemical potential in our experiments induced changes in both the elastic energy and electrostatic interactions. Our results quantitatively demonstrate that the mechanism of dopant segregation on perovskite oxides includes both the elastic and electrostatic energy contributions. A smaller size mismatch between the host and dopant cations and a chemically expanded lattice were found to reduce the segregation level of the dopant and to enable more stable cathode surfaces. Ca-doped LaMnO3 was found to have the most stable surface composition with the least cation segregation among the compositions surveyed. The diffusion kinetics of the larger dopants, Ba and Sr, was found to be slower and can kinetically trap the segregation at reduced temperatures despite the larger elastic energy driving force. Lastly, scanning probe image contrast showed that the surface chemical heterogeneities made of dopant oxides upon segregation were electronically insulating. The consistency between the results obtained from experiments, DFT calculations, and analytical theory in this work provides a predictive capability to tailor the cathode surface compositions for high-performance SOFCs.

Journal ArticleDOI
TL;DR: In this article, a two-step deposition technique was used for preparing CH3NH3PbI3 perovskite solar cells using ZrO2 and TiO2 as a mesoporous layer, achieving an efficiency of 10.8% and 9.5% under 1000 W m−2 illumination.
Abstract: A two-step deposition technique is used for preparing CH3NH3PbI3 perovskite solar cells. Using ZrO2 and TiO2 as a mesoporous layer, we obtain an efficiency of 10.8% and 9.5%, respectively, under 1000 W m−2 illumination. The ZrO2 based solar cell shows higher photovoltage and longer electron lifetime than the TiO2 based solar cell.

Journal ArticleDOI
TL;DR: A novel organometal halide perovskite (CH3NH3PbI2Br) is synthesized and used as a visible light absorber to sensitize one-dimensional TiO2 nanowire arrays (NWAs) for all-solid-state hybrid solar cells.
Abstract: A novel organometal halide perovskite (CH3NH3PbI2Br) is synthesized and used as a visible light absorber to sensitize one-dimensional (1D) TiO2 nanowire arrays (NWAs) for all-solid-state hybrid solar cells. It achieved a power conversion efficiency (PCE) of 4.87% and an open circuit voltage (Voc) of 0.82 V, both higher than those of its analogue CH3NH3PbI3.

Journal ArticleDOI
TL;DR: In this paper, a combination of symmetry arguments and first-principles calculations is used to explore the connection between structural distortions and ferroelectricity in the perovskite family of materials.
Abstract: We use a combination of symmetry arguments and first-principles calculations to explore the connection between structural distortions and ferroelectricity in the perovskite family of materials. We explain the role of octahedral rotations in suppressing ferroelectricity in these materials and show that, as the tolerance factor decreases, rotations alone cannot fully suppress ferroelectricity. Our results show that it is cation displacements (“hidden” in Glazer notation) that accompany the rotations, rather than the rotations themselves, that play the decisive role in suppressing ferroelectricity in these cases. We use the knowledge gained in our analysis of this problem to explain the origin of ferroelectricity in R3c materials such as FeTiO3 and ZnSnO3 and to suggest strategies for the design and synthesis of new perovskite ferroelectrics. Our results have implications not only for the fundamental crystal chemistry of the perovskites but also for the discovery of new functional materials.

Journal ArticleDOI
TL;DR: In this article, the use of perovskite oxides in two-step, solar-thermochemical water or carbon dioxide splitting cycles was reported, and it was shown that LaAlO3 doped with Mn and Sr will efficiently split both gases.
Abstract: The increasing global appetite for energy within the transportation sector will inevitably result in the combustion of more fossil fuel. A renewable-derived approach to carbon-neutral synthetic fuels is therefore needed to offset the negative impacts of this trend, which include climate change. In this communication we report the use of nonstoichiometric perovskite oxides in two-step, solar-thermochemical water or carbon dioxide splitting cycles. We find that LaAlO3 doped with Mn and Sr will efficiently split both gases. Moreover the H2 yields are 9× greater, and the CO yields 6× greater, than those produced by the current state-of-the-art material, ceria, when reduced at 1350 °C and re-oxidized at 1000 °C. The temperature at which O2 begins to evolve from the perovskite is fully 300 °C below that of ceria. The materials are also very robust, maintaining their redox activity over at least 80 CO2 splitting cycles. This discovery has profound implications for the development of concentrated solar fuel technologies.

Journal ArticleDOI
TL;DR: The spinel/perovskiteTwo-dimensional electron gas, where the two-dimensional conduction character is revealed by quantum magnetoresistance oscillations, is found to result from interface-stabilized oxygen vacancies confined within a layer of 0.9 nm in proximity to the interface.
Abstract: Highly mobile electrons at the interface of two perovskite oxides are of considerable interest for electronic applications. In this work, the discovery of such an electron gas at the interface of a spinel and a perovskite oxide represents a new approach to look for oxide systems with enhanced properties.

Journal ArticleDOI
TL;DR: In this article, the effect of TiO2 film thickness on the charge transport, recombination, and device characteristics of perovskite (CH3NH3)PbI3 sensitized solar cells using iodide-based electrolytes was investigated.
Abstract: We report on the effect of TiO2 film thickness on the charge transport, recombination, and device characteristics of perovskite (CH3NH3)PbI3 sensitized solar cells using iodide-based electrolytes. (CH3NH3)PbI3 is relatively stable in a nonpolar solvent (e.g., ethyl acetate) with a low iodide concentration (e.g., 80 mM). Frequency-resolved modulated photocurrent/photovoltage spectroscopies show that increasing TiO2 film thickness from 1.8 to 8.3 μm has little effect on transport but increases recombination by more than 10-fold, reducing the electron diffusion length from 16.9 to 5.5 μm, which can be explained by the higher degree of iodide depletion within the TiO2 pores for thicker films. The changes of the charge-collection and light-absorption properties of (CH3NH3)PbI3 sensitized cells with varying TiO2 film thickness strongly affect the photocurrent density, photovoltage, fill factor, and solar conversion efficiency. Developing alternative, compatible redox electrolytes is important for (CH3NH3)PbI3 o...

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TL;DR: The ab-initio study supports the picture of an orbital-order-induced ferroelectricity, a rare example of dipolar ordering caused by electronic degrees of freedom, and offers an important starting point for tailoring multiferroic properties in this emerging class of materials for various technological applications.
Abstract: There is great interest in hybrid organic-inorganic materials such as metal-organic frameworks (MOFs). The compounds [C(NH$_{2}$)$_{3}$]M(HCOO)$_{3}$, where M=Cu$^{2+}$ or Cr$^{2+}$ are Jahn-Teller (JT) active ions, are MOF with perovskite topology which crystallizes in polar space group Pna2$_{1}$. In inorganic compounds, octahedral tilting and Jahn-Teller structural distortions are usually non-polar distortions. However, in this MOF cooperative interactions between the antiferro-distortive distortions of the framework and the C(NH2)$_{3}$ organic cation via hydrogen bonding breaks the inversion symmetry and induces a ferroelectric polarization.[Angew. Chem. Int. Ed. 50, 5847, 2011] Our ab-initio study supports the picture of an orbital-order-induced ferroelectricity, a rare example of dipolar ordering caused by electronic degrees of freedom. The switching of polarization direction implies the reversal of the weak ferromagnetic component. The microscopic mechanism in this JT-based MOF with ABX$_{3}$ perovskite structure displays a Hybrid Improper Ferroelectric (HIF) state, arising from a trilinear coupling between different structural deformations that comprise tilting, rotations and Jahn-Teller distortions of both the BX$_{3}$ framework and the organic cation at the A sites. Since these distortion modes in perovskite-inorganic compounds usually freeze-in at elevated temperatures, the trilinear coupling in MOF compounds may provide an interesting route towards high-temperature multiferroicity. These results offer an important starting point for tailoring multiferroic properties in this emerging class of materials for various technological applications. In particular, the high tunability of the ferroelectric polarization by means of the modification of the organic A cation has been recently shown[J. Am. Chem. Soc. 135 18126 (2013)]