54 research outputs found
Cu-In Halide Perovskite solar absorbers
The long-term chemical instability and the presence of toxic Pb in otherwise
stellar solar absorber APbX have hindered their large-scale
commercialization. Previously explored ways to achieve Pb-free halide
perovskites involved replacing Pb with other similar M cations in
ns electron configuration, e.g., Sn or by Bi (plus Ag),
but unfortunately this showed either poor stability (M = Sn) or weakly
absorbing oversized indirect gaps (M = Bi), prompting concerns that perhaps
stability and good optoelectronic properties might be contraindicated. Herein,
we exploit the electronic structure underpinning of classic Cu[In,Ga]Se
(CIGS) chalcopyrite solar absorbers to design Pb-free halide perovskites by
transmuting 2Pb to the pair [B + C]. The resulting group of
double perovskites with formula ABCX (A = K, Rb, Cs; B = Cu, Ag; C =
Ga, In; X = Cl, Br, I) benefits from the ionic, yet narrow-gap character of
halide perovskites, and at the same time borrows the advantage of the strong
and rapidly rising Cu(d)/Se(p) Ga/In(s/p)
valence-to-conduction-band absorption spectra known from CIGS. This constitutes
a new group of CuIn-based Halide Perovskite (CIHP). Our first-principles
calculations guided by such design principles indicate that the CIHPs class has
members with clear thermodynamic stability, showing rather strong direct-gap
optical transitions, and manifesting a wide-range of tunable gap values (from
zero to about 2.5 eV) and combination of light electron and heavy-light hole
effective masses. Materials screening of candidate CHIPs then identifies the
best-of-class Rb[CuIn]Cl, Rb[AgIn]Br and Cs[AgIn]Br,
having direct band gaps of 1.36, 1.46 and 1.50 eV, and a theoretical
spectroscopic limited maximal efficiency comparable to chalcopyrites and
CHNHPbI.Comment: 25 pages, 6 figure
Design of Lead-Free Inorganic Halide Perovskites for Solar Cells via Cation-Transmutation
Hybrid organic-inorganic halide perovskites with the prototype material of
CHNHPbI have recently attracted intense interest as low-cost
and high-performance photovoltaic absorbers. Despite the high power conversion
efficiency exceeding 20% achieved by their solar cells, two key issues -- the
poor device stabilities associated with their intrinsic material instability
and the toxicity due to water soluble Pb -- need to be resolved before
large-scale commercialization. Here, we address these issues by exploiting the
strategy of cation-transmutation to design stable inorganic Pb-free halide
perovskites for solar cells. The idea is to convert two divalent Pb ions
into one monovalent M and one trivalent M ions, forming a rich
class of quaternary halides in double-perovskite structure. We find through
first-principles calculations this class of materials have good phase stability
against decomposition and wide-range tunable optoelectronic properties. With
photovoltaic-functionality-directed materials screening, we identify eleven
optimal materials with intrinsic thermodynamic stability, suitable band gaps,
small carrier effective masses, and low excitons binding energies as promising
candidates to replace Pb-based photovoltaic absorbers in perovskite solar
cells. The chemical trends of phase stabilities and electronic properties are
also established for this class of materials, offering useful guidance for the
development of perovskite solar cells fabricated with them.Comment: pages 19, 4 figures in main tex
Pressure-induced emission of cesium lead halide perovskite nanocrystals.
Metal halide perovskites (MHPs) are of great interest for optoelectronics because of their high quantum efficiency in solar cells and light-emitting devices. However, exploring an effective strategy to further improve their optical activities remains a considerable challenge. Here, we report that nanocrystals (NCs) of the initially nonfluorescent zero-dimensional (0D) cesium lead halide perovskite Cs4PbBr6 exhibit a distinct emission under a high pressure of 3.01 GPa. Subsequently, the emission intensity of Cs4PbBr6 NCs experiences a significant increase upon further compression. Joint experimental and theoretical analyses indicate that such pressure-induced emission (PIE) may be ascribed to the enhanced optical activity and the increased binding energy of self-trapped excitons upon compression. This phenomenon is a result of the large distortion of [PbBr6]4- octahedral motifs resulting from a structural phase transition. Our findings demonstrate that high pressure can be a robust tool to boost the photoluminescence efficiency and provide insights into the relationship between the structure and optical properties of 0D MHPs under extreme conditions
Imaging of the Atomic Structure of All-Inorganic Halide Perovskites
All-inorganic halide perovskites are promising materials for optoelectronic applications. The surface or interface structure of the perovskites plays a crucial role in determining the optoelectronic conversion efficiency, as well as the material stability. A thorough understanding of surface atomic structures of the inorganic perovskites and their contributions to their optoelectronic properties and stability is lacking. Here we show a scanning tunneling microscopy investigation on the atomic and electronic structure of CsPbBr3 perovskite. Two different surface structures with a stripe and an armchair domain are identified, which originates from a complex interplay between Cs cations and Br anions. Our findings are further supported and correlated with density functional theory calculations and photoemission spectroscopy measurements. The stability evaluation of photovoltaic devices indicates a higher stability for CsPbBr3 in comparison with MAPbBr3, which is closely related to the low volatility of Cs from the perovskite surface
Research on Electromagnetic Vibration Characteristics of a Permanent Magnet Synchronous Motor Based on Multi-Physical Field Coupling
Background and Purpose: The stator vibration characteristics are comprehensively mastered by considering the influence of winding and the housing structure on the stator modes. This effect is neglected in the research field of electromagnetic vibration of permanent magnet synchronous motors (PMSMs). Methods: The radial air-gap flux density equations and PMSM’s electromagnetic force density are derived, and then the harmonic characteristics of electromagnetic force density are studied. An equivalent finite element model of the stator is proposed that investigates the impacts of the winding and stator housing rules on the stator modal frequency. Finally, the harmonic response and acoustic analyses of electromagnetic vibration are carried out based on multi-physics field coupling. Results: The equivalent radiated power distribution laws and acoustic field of motor electromagnetic vibration under transient operating conditions are obtained. The theoretical analysis results are consistent with the experimental results. Conclusion: The obtained results show that the spatial order of the radial electromagnetic force is not equal to the order of the radial mode of the motor stator. The reason for this is that structural resonance is induced when the frequency components of the spatial radial electromagnetic force are coupled with the intrinsic frequency of the stator
FAULT FEATURE EXTRACTION METHOD FOR ROLLER BEARINGS BASED ON LCD AND LOCAL HILBERT MARGINAL ENERGY SPECTRUM
Based on the definition of local Hilbert marginal energy spectrum,a fault feature extraction method for roller bearings is further proposed based on LCD and local Hilbert marginal energy spectrum. By using LCD,an original rolling bearing vibration signal could be adaptively decomposed into a number of intrinsic scale components( ISC),and then the time-frequency distribution( TFD) could be obtained by applying Hilbert demodulation to all the components. According to the distribution of the signal energy revealed by the TFD,a local Hilbert marginal energy spectrum could be acquired once the lower and upper limit frequency for the corresponding frequency band are determined. Then the signal energy over this frequency band could be computed subsequently and regarded as the fault feature parameter. The analysis results from rolling bearing vibration signals show that the proposed approach can effectively extract the fault feature information
MSNet: A Multi-Stream Fusion Network for Remote Sensing Spatiotemporal Fusion Based on Transformer and Convolution
Remote sensing products with high temporal and spatial resolution can be hardly obtained under the constrains of existing technology and cost. Therefore, the spatiotemporal fusion of remote sensing images has attracted considerable attention. Spatiotemporal fusion algorithms based on deep learning have gradually developed, but they also face some problems. For example, the amount of data affects the model’s ability to learn, and the robustness of the model is not high. The features extracted through the convolution operation alone are insufficient, and the complex fusion method also introduces noise. To solve these problems, we propose a multi-stream fusion network for remote sensing spatiotemporal fusion based on Transformer and convolution, called MSNet. We introduce the structure of the Transformer, which aims to learn the global temporal correlation of the image. At the same time, we also use a convolutional neural network to establish the relationship between input and output and to extract features. Finally, we adopt the fusion method of average weighting to avoid using complicated methods to introduce noise. To test the robustness of MSNet, we conducted experiments on three datasets and compared them with four representative spatiotemporal fusion algorithms to prove the superiority of MSNet (Spectral Angle Mapper (SAM) < 0.193 on the CIA dataset, erreur relative global adimensionnelle de synthese (ERGAS) < 1.687 on the LGC dataset, and root mean square error (RMSE) < 0.001 on the AHB dataset)
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