Recent progress on low dimensional perovskite solar cells

Low dimensional perovskites have recently attracted much attention due to their vertical growth of crys- talline orientation, excellent film morphology, and long-term humidity, light, and heat stability, How- ever, low dimensional perovskites suffer fl＇om low power conversion efficiency （PCE） with respect to their three dimensional analogues. Therefore, it is imperative to find excellent low-dimensional perovskite materials for improving the PCE. Previous work has demonstrated that bulkier organic molecules, e,g., C6Hs（CH2）2NH3＋ （PEA＋）, CH3（CH2）3NH3＋（n-BAT, iso-BA＋）, C2H4NH3 ＋, and polyethylenimine cations （PEI＋）, play an important role in the formation of low-dimensional perovskites. In this review, we review the recent development of low dimensional perovskites for solar cells application in terms of film preparation, photophysics, and stability of perovskites, as well as the related device structure and physics. We have also discussed the future development of low-dimensional perovskites from materials design, fabri- cation processes, and device structure.

Seismic data reconstruction based on low dimensional manifold model

Seismic data reconstruction is an essential and yet fundamental step in seismic data processing workflow,which is of profound significance to improve migration imaging quality,multiple suppression effect,and seismic inversion accuracy.Regularization methods play a central role in solving the underdetermined inverse problem of seismic data reconstruction.In this paper,a novel regularization approach is proposed,the low dimensional manifold model(LDMM),for reconstructing the missing seismic data.Our work relies on the fact that seismic patches always occupy a low dimensional manifold.Specifically,we exploit the dimension of the seismic patches manifold as a regularization term in the reconstruction problem,and reconstruct the missing seismic data by enforcing low dimensionality on this manifold.The crucial procedure of the proposed method is to solve the dimension of the patches manifold.Toward this,we adopt an efficient dimensionality calculation method based on low-rank approximation,which provides a reliable safeguard to enforce the constraints in the reconstruction process.Numerical experiments performed on synthetic and field seismic data demonstrate that,compared with the curvelet-based sparsity-promoting L1-norm minimization method and the multichannel singular spectrum analysis method,the proposed method obtains state-of-the-art reconstruction results.

Studies of Characterization of Microstructures for Low Dimensional Materials

The characterization of microstructure for three kinds of typical low dimensional materials,such as ultrafine particle(zero- dimension),whisker(one- dimension)and thin film(two-dimensions),has been carried out.The methods and criteria for the characterization are investigated and introduced.Some interesting results of the characterization are reported.

LOW-DIMENSIONAL STRUCTURES:SP ARSE CODING FOR NEURONAL ACTIVITY

Neuronal ensemble activity codes working memory.In this work,we developed a neuronal ensemble sparse coding method,which can effectively reduce the dimension of the neuronal activity and express neural coding.Multichannel spike trains were recorded in rat prefrontal cortex during a work memory task in Y-maze.As discretesignals,spikes were transferred into cont inuous signals by estinating entropy.Then the normalized continuous signals were decomposed via non-negative sparse met hod.The non-negative components were extracted to reconstruct a low-dimensional ensemble,while none of the feature components were missed.The results showed that,for well-trained rats,neuronal ensemble activities in the prefrontal cortex changed dynamically during the.working memory task.And the neuronal ensemble is more explicit via using non-negative sparse coding.Our results indicate that the neuronal ensemblesparse coding method can effectively reduce the dimnension of neuronal activity and it is a useful tool to express neural coding.

Investigation of dimensionality in superconducting NbN thin film samples with different thicknesses and NbTiN meander nanowire samples by measuring the upper critical field

We study superconducting properties of NbN thin film samples with different thicknesses and an ultra-thin NbTiN meander nanowire sample.For the ultra-thin samples,we found that the temperature dependence of upper critical field(Hc2)in parallel to surface orientation shows bending curvature close to critical temperature Tc,suggesting a two-dimensional(2D)nature of the samples.The 2D behavior is further supported by the angular dependence measurements of Hc2 for the thinnest samples.The temperature dependence of parallel upper critical field for the thick films could be described by a model based on the anisotropic Ginzburg-Landau theory.Interestingly,the results measured in the field perpendicular to the film surface orientation show a similar bending curvature but in a much narrow temperature region close to Tc for the ultra-thin samples.We suggest that this feature could be due to suppression of pair-breaking caused by local in-homogeneity.We further propose the temperature dependence of perpendicular Hc2 as a measure of uniformity of superconducting ultra-thin films.For the thick samples,we find that Hc2 shows maxima for both parallel and perpendicular orientations.The Hc2 peak for the perpendicular orientation is believed to be due to the columnar structure formed during the growth of the thick films.The presence of columnar structure is confirmed by transmission electron microscopy(TEM).In addition,we have measured the angular dependence of magneto-resistance,and the results are consistent with the Hc2 data.

Electronic transport properties of topological insulator films and low dimensional superconductors

In this review, we present a summary of some recent experiments on topological insulators （TIs） and superconducting nanowires and fihns. Electron electron interaction （EEI）, weak anti-localization （WAL） and anisotropic magneto-resistance （AMR） effect fbund in topological insulator fihns by transport measurements are reported. Then, transport properties of superconducting films, bridges and nanowires and proximity effect in non-superconducting nanowires are described. Finally, the interplay between topological insulators and superconductors （SCs） is also discussed.

Low‐dimensional material supported single‐atom catalysts for electrochemical CO_(2) reduction

Converting CO_(2) emissions to valuable carbonaceous chemicals/fuels under mild conditions provides a sustainable way to maintain carbon balance and alleviate the energy shortage.Low‐dimensional material(LDM)supported single‐atom catalysts(SACs)have been attracted significant attention for electrochemical CO_(2) reduction reaction(ECR)in recent years.This is mainly because integrating the single‐atoms and LDMs can inherit the advantages of themselves and the synergy effects between them are potential to enhance the ECR performance.In this review,we summarized the strategies for synthesizing LDM supported SACs for ECR,and different LDM supported SACs for ECR have been briefly introduced.Moreover,some optimization strategies for LDM supported SACs towards CO_(2) electroreduction are highlighted.At the end of this review,the perspectives and challenges of LDM supported SACs for ECR are provided.

The roles of black phosphorus in performance enhancement of halide perovskite solar cells

Hybrid organic-inorganic perovskite solar cells(PSCs) are considered to be the most promising thirdgeneration photovoltaic(PV) technology with the most rapid rate of increase in the power conversion efficiency(PCE). To date, their PCE values are comparable to the established photovoltaic technologies such as crystalline silicon. Intensive research activities associated with PSCs have been being performed,since 2009, aiming to further boost the device performance in terms of efficiency and stability via different strategies in order to accelerate the progress of commercialization. The emerging 2 D black phosphorus(BP) is a novel class of semiconducting material owing to its unique characteristics, allowing them to become attractive materials for applications in a variety of optical and electronic devices, which have been comprehensively reviewed in the literature. However, comprehensive reviews focusing on the application of BP in PSCs are scarce in the community. This review discusses the research works with the incorporation of BP as a functional material in PSCs. The methodology as well as the effects of employing BP in different regions of PSCs are summarized. Further challenges and potential research directions are also highlighted.

Ruddlesden–Popper Perovskite for Stable Solar Cells

Three-dimensional metal-halide perovskites have emerged as promising light harvesting materials for converting sunlight to electricity in the last few years.High power conversion efficiency of 23.3%has been demonstrated.However,the main challenge that currently limits the application of the perovskite solar cells is the long-term stability,which has ambient,thermal,and photo stability weaknesses.

Extraction and application of the low dimensional dynamical component from underwater acoustic target radiating noise

Signal processing in phase space based on nonlinear dynamics theory is a new method for underwater acoustic signal processing. One key problem when analyzing actual acoustic signal in phase space is how to reduce the noise and lower the embedding dimen- sion. In this paper, local-geometric-projection method is applied to obtain fow dimensional element from various target radiating noise and the derived phase portraits show obviously low dimensional attractors. Furthermore, attractor dimension and cross prediction error are used for classification. It concludes that combining these features representing the geometric and dynamical properties respectively shows effects in target classification.

Scalable preparation of water-soluble ink of few-layered WSe2 nanosheets for large-area electronics

Few-layer two-dimensional(2D)semiconductor nanosheets with a layer-dependent band gap are attractive building blocks for large-area thin-film electronics.A general approach is developed to fast prepare uniform and phase-pure 2HWSe2 semiconducting nanosheets at a large scale,which involves the supercritical carbon dioxide(SC-CO2)treatment and a mild sonication-assisted exfoliation process in aqueous solution.The as-prepared 2H-WSe2 nanosheets preserve the intrinsic physical properties and intact crystal structures,as confirmed by Raman,x-ray photoelectron spectroscopy(XPS),and scanning transmission electron microscope(STEM).The uniform 2H-WSe2 nanosheets can disperse well in water for over six months.Such good dispersivity and uniformity enable these nanosheets to self-assembly into thickness-controlled thin films for scalable fabrication of large-area arrays of thin-film electronics.The electronic transport and photoelectronic properties of the field-effect transistor based on the self-assembly 2H-WSe2 thin film have also been explored.

Self-assembling nanoarchitectonics of low dimensional semiconductors for circularly polarized luminescence

Recently,the development of materials with circularly polarized luminescence(CPL)has attracted numerous attentions owing to their potential applications in various fields.Among diverse mechanisms for the origin of chiroptical properties in low dimensional semiconductors(LDS),the self-assembly approach provides a powerful technique for acquisition of strong chiroptical activity.Benefiting from this approach,LDS could be endowed with CPL in which the dissymmetry factor,a vital parameter for evaluating the performance of CPL,could be greatly improved.In this review,state-of-the-art of selfassembled LDS will be summarized.The current challenges and perspectives in this emerging field are also presented.This review could not only provide insights of the fundamentals of self-assembled chirality,but also shine light for designing CPL-active functional nanomaterials toward their applications based on novel optoelectronic devices.

Spurious Solutions in the Multiband Effective Mass Theory Applied to Low Dimensional Nanostructures

In this paper we analyze a long standing problem of the appearance of spurious,non-physical solutions arising in the application of the effective mass theory to low dimensional nanostructures.The theory results in a system of coupled eigenvalue PDEs that is usually supplemented by interface boundary conditions that can be derived from a variational formulation of the problem.We analyze such a system for the envelope functions and show that a failure to restrict their Fourier expansion coeffi-cients to small k components would lead to the appearance of non-physical solutions.We survey the existing methodologies to eliminate this difficulty and propose a simple and effective solution.This solution is demonstrated on an example of a two-band model for both bulk materials and low-dimensional nanostructures.Finally,based on the above requirement of small k,we derive a model for nanostructures with cylindrical symmetry and apply the developed model to the analysis of quantum dots using an eight-band model.

LOW FREQUENCY WAVE FORCFES ON TWO DIMENSIONAL FLOATING BODIES

Simulating incident group wave with narrow spectrum by nonlinear slowly modulated Stoking wave train and using Multiple Scales Method.problem of the second-order low frequency diffraction of group waves on a two-di mensionai floating body has been studied.The first-order and second-order low frequency diffraction potentials are derived,which lead to the second-order and third-order low frequency forces respectively.It is shown thai the sec- ond-order low frequency force generated by first-order low frequency diffraction potentials is verticcal to undis- turbed free surface,and is directly proportional to square of envelope amplitude of incident wave and to waterline width of floating body.The horizontal low frequency forces are caused by the second-order low frequency diffrac- tion potential.To determine it only two linear boundary value problems are necessary to be solved.

All-optical inverter based on carbon nanotube-polyvinyl alcohol thin film

All-optical light control plays an important role in optical signal processing and communications.In this Letter,we demonstrate an all-optical inverter using carbon nanotube(CNT)-polyvinyl alcohol(PVA)thin film and obtain a long-time stable output due to the environmental insensitivity of the device.The thermo-optic effect in the CNT-PVA thin film generates a thermal lens and modifies the beam propagation in the thin film.The obtained all-optical inverter has a front(trailing)time constant of∼55μs(44μs)for 1550 nm signal pulses and∼7 kHz response bandwidth.