Efficient and Air-Stable Planar Perovskite Solar Cells Formed on Graphene-Oxide-Modified PEDOT:PSS Hole Transport Layer

As a hole transport layer, PEDOT:PSS usually limits the stability and efficiency of perovskite solar cells(PSCs) due to its hygroscopic nature and inability to block electrons. Here, a graphene-oxide(GO)-modified PEDOT:PSS hole transport layer was fabricated by spin-coating a GO solution onto the PEDOT:PSS surface. PSCs fabricated on a GO-modified PEDOT:PSS layer exhibited a power conversion efficiency(PCE) of 15.34%, which is higher than 11.90% of PSCs with the PEDOT:PSS layer.Furthermore, the stability of the PSCs was significantly improved, with the PCE remaining at 83.5% of the initial PCE values after aging for 39 days in air. The hygroscopic PSS material at the PEDOT:PSS surface was partlyremoved during spin-coating with the GO solution, which improves the moisture resistance and decreases the contact barrier between the hole transport layer and perovskite layer. The scattered distribution of the GO at the PEDOT:PSS surface exhibits superior wettability, which helps to form a high-quality perovskite layer with better crystallinity and fewer pin holes. Furthermore, the hole extraction selectivity of the GO further inhibits the carrier recombination at the interface between the perovskite and PEDOT:PSS layers. Therefore, the cooperative interactions of these factors greatly improve the light absorption of the perovskite layer, the carrier transport and collection abilities of the PSCs, and especially the stability of the cells.

Effective Improvement of the Photovoltaic Performance of Carbon-Based Perovskite Solar Cells by Additional Solvents

A solvent-assisted methodology has been developed to synthesize CH_3NH_3 PbI_3perovskite absorber layers.It involved the use of a mixed solvent of CH_3NH_3 I,PbI_2,c-butyrolactone,and dimethyl sulfoxide(DMSO) followed by the addition of chlorobenzene(CB).The method produced ultra-flat and dense perovskite capping layers atop mesoporous TiO_2 films,enabling a remarkable improvement in the performance of free hole transport material(HTM) carbon electrode-based perovskite solar cells(PSCs).Toluene(TO) was also studied as an additional solvent for comparison.At the annealing temperature of 100 °C,the fabricated HTM-free PSCs based on drop-casting CB demonstrated power conversion efficiency(PCE) of 9.73 %,which is 36 and 71 % higher than those fabricated from the perovskite films using TO or without adding an extra solvent,respectively.The interaction between the PbI_2–DMSO–CH_3NH_3I intermediate phase and the additional solvent was discussed.Furthermore,the influence of the annealing temperature on the absorber film formation,morphology,and crystalline structure was investigated and correlated with the photovoltaic performance.Highly efficient,simple,and stable HTM-free solar cells with a PCE of 11.44 % were prepared utilizing the optimum perovskite absorbers annealed at 120 °C.

Fabrication and Evaluation of Low-cost Cu_2ZnSn(S,Se)_4 Counter Electrodes for Dyesensitized Solar Cells

We explore a simple and eco-friendly approach for preparing CZTS powders and a screen-printing process for Cu_2ZnSn(S,Se)_4(CZTSSe) counter electrodes(CEs) in dye-sensitized solar cells(DSCs). Cu_2ZnSnS_4(CZTS) nanoparticles have been synthesized via a hydrazine-free solvothermal approach without the assistance of organic ligands. CZTS has been prepared by directly drop-casting the CZTS ink on the cleaned FTO glass, while CZTSSe CEs have been fabricated by screen-printing CZTS pastes, followed by post selenization using Se vapor obtained from elemental Se pellets. The crystal structure, composition and morphology of the as-deposited CZTS nanoparticles and CZTSSe electrodes are characterized by X-ray diffractometer, energy dispersive spectrometer, field emission scanning electron microscopy and transmission electron microscopy.The electrochemical properties of CZTS, CZTSSe and Pt CE based DSCs are examined and analyzed by electrochemical impedance spectroscopy. The prepared CZTS and CZTSSe CEs exhibit a cellular structure with high porosity. DSCs fabricated with CZTSSe CEs achieve a power conversion efficiency of 5.75% under AM 1.5 G illumination with an intensity of 100 m W/cm^2, which is higher than that(3.22%) of the cell using the CZTS CE. The results demonstrate that the CZTSSe CE possesses good electrocatalytic activity for the reduction of charge carriers in electrolyte. The comprehensive CZTSSe CE process is cheap and scalable. It can make large-scale electro-catalytic film fabrication cost competitive for both energy harvesting and storage applications.

Investigation of europium(Ⅲ)-doped ZnS for immunoassay

Biofunctional europium（Ⅲ）-doped ZnS（ZnS：Eu） nanocrystals are prepared by a sol–gel method. The characteristic luminescence of ZnS：Eu is used as a probe signal to realize sensitive immunoassay. The luminescence intensity of the Eu^（3＋） in the ZnS matrix shows strong concentration dependence, and the optimal doping concentration is 4%. However,the emission wavelengths of the ZnS：Eu nanocrystals are not dependent on doping concentration nor the temperature（from 100 K to 300 K）. Our results show that these features allow for reliable immunoassay. Human immunoglobulin, used as a target analyte, is captured by antibody modified ZnS：Eu probe and is finally enriched on gold substrate for detection.High specificity of the assay is demonstrated by control experiments. The linear detection range is 10 nM –800 nM, and the detection limit is about 9.6 nM.

Asymmetric magnetoimpedance effect and dipolar interactions of FINEMET/SiO_(2)/FePd composite ribbons

The dipolar interactions are investigated through the asymmetric magneto-impedance in FINEMET/SiO_(2)/FePd composite ribbons.The interface between the hard(FePd layer)phase and soft(FINEMET ribbon)phase is coherent by SiO_(2)layer in FINEMET/SiO_(2)/FePd composite ribbons,which effectively induces dipolar interactions.The contribution of dipolar interaction to the bias field(Hb)by asymmetrical giant magneto-impedance and magnetic properties is analyzed.The results show that Hb response decreases with the increase of the SiO_(2)layer thickness,indicating that the linear region near-zero field can be tuned by the thickness of SiO_(2)layer.These results allow the GMI ratio(58%)and characteristic frequency(500 kHz)to be optimized.The transverse and longitudinal magnetic domain structures of FINEMET ribbon and FePd film are confirmed,respectively.The composite ribbons with high GMI ratio and low frequency can be applied to linear magnetic sensors.

Enhancement of corona discharge induced wind generation with carbon nanotube and titanium dioxide decoration

Dip-coated double-wall carbon nanotubes(DWCNTs) and titanium dioxide(TiO2) sol have been prepared and smeared onto the tip of a conductive iron needle which serves as the corona discharge anode in a needle-cylinder corona system.Compared with the discharge electrode of a CNT-coated needle tip, great advancements have been achieved with the TiO_2/CNT-coated electrode, including higher discharge current, ionic wind velocity, and energy conversion efficiency,together with lower corona onset voltage and power consumption.Several parameters related to the discharge have been phenomenologically and mathematically studied for comparison.Thanks to the morphology reorientation of the CNT layer and the anti-oxidation of TiO_2, better performance of corona discharge induced wind generation of the TiO2/CNT-coated electrode system has been achieved.This novel decoration may provide better thoughts about the corona discharge application and wind generation.

Dye-sensitized Solar Cells with Higher J_(sc) by Using Polyvinylidene Fluoride Membrane Counter Electrodes

A flexible counter electrode(CE) for dye-sensitized solar cells(DSCs) has been fabricated using a micro-porous polyvinylidene fluoride membrane as support media and sputtered Pt as the catalytic material.Non-conventional structure DSCs have been developed by the fabricated CEs. The Pt metal was sputtered onto one surface of the membrane as the catalytic material. DSCs were assembled by attaching the Ti O2 electrode to the membrane surface without Pt coating. The membrane was with cylindrical pore geometry. It served not only as a substrate for the CE but also as a spacer for the DSC. The fabricated DSC with the flexible membrane CE showed higher photocurrent density than the conventional sandwich devices based on chemically deposited Pt/FTO glass, achieving a photovoltaic conversion efficiency of 4.43%. The results provides useful information in investigation and development of stable, low-cost, simple-design, flexible and lightweight DSCs.

Magnetic Tunnel Junction Based on MgO Barrier Prepared by Natural Oxidation and Direct Sputtering Deposition

Magnetic tunnel junctions(MTJs) based on MgO barrier have been fabricated by sputtering single crystal MgO target and metal Mg target, respectively, using magnetic sputtering system Nordiko 2000. MgO barriers have been formed by a multi-step deposition and natural oxidization of Mg layer. Mg layer thickness,oxygen flow rate and oxidization time were adjusted and the tunnel magnetoresistance(TMR) ratio of optimal MTJs is over 60% at annealing temperature 385. The(001) MgO crystal structure was obtained when the separation distance between MgO target and substrate is less than 6 cm. The TMR ratio of most MgO based MTJs are over 100% at the separation distance of 5 cm and annealing temperature 340. The TMR ratios of MTJs are almost zero when the separation distance ranges from 6 to 10 cm, due to the amorphous nature of the MgO film.

Giant Magneto-impedance Effect in Composite Wires with Different Core Layer

Composite structure materials were potential sensing elements for magnetic sensors due to Giant magnetoimpedance(GMI) effect. Two kinds of composite wires with different magnetic/non-magnetic structures were fabricated by using electroless deposition methods and the magnetoimpedance properties were investigated. The maximum GMI ratio of 114% was acquired at 60 MHz in the composite wires with a ferromagnetic core, whereas, 116% of maximum GMI ratio was found in the composite wires with a conductive core at low frequency of 600 k Hz. These results exhibit that the GMI ratio reaches the maximum when magnetoresistance ratio ?R/R and magnetoinductance ratio ?X/X make the comparative contributions to the total magnetoimpedance(MI). The obvious GMI effect obtained in the composite wires with conductive core frequency may provide a candidate for applications in magnetic sensors, especially at low frequencies.

Influence of an Electronic Field on the GMI Effect of Fe-based Nanocrystalline Microwire

In this work, a Fe-based nanocrystalline microwire of 20 mm in length and 25 μm in diameter was placed in the center of a 316 stainless steel pipe. The pipe was 500 μm in diameter and a little shorter than the microwire. A series of voltages were applied on the pipe to study the influence of the electrical field on the Giant-Magneto-Impedance(GMI) effect of the microwire. Experimental results showed that the electronic field between the wire and the pipe reduced the hysteresis of the GMI effect. The results were explained based on equivalent circuit and eddy current consumptions analysis.

Magneto-Impedance Effect of Composite Wires Prepared by Chemical Plating under DC Current

CuBe composite wires of 100 μm in diameter coated with a layer of NiCoP were prepared by a chemical plating method under DC current(CPUDC). The influences of DC current on coating morphology,deposition rate, composition, giant magneto-impedance(GMI) effect and magnetic properties were investigated.It was shown that the circumferential domain structure of coating layer was induced by the DC current going through the wires. A maximum GMI ratio of 870% was obtained in the composite wire prepared under 150 m A and tested at 180 k Hz. It is 30 times higher than that of the composite wire plated in the same condition by conventional chemical plating method, indicating that CPUDC is an easy and effective approach to obtain composite wires and its applications will be further extended on magnetic sensors.

Efficiency Enhancement of Inverted Polymer Solar Cells Using Ionic Liquid-functionalized Carbon Nanoparticles-modified ZnO as Electron Selective Layer

ZnO thin film was fabricated on tin-doped indium oxide electrode as an electron selective layer of inverted polymer solar cells using magnetron sputtering deposition. Ionic liquid-functionalized carbon nanoparticles(ILCNs) film was further deposited onto ZnO surfaces by drop-casting ILCNs solution to improve interface properties. The power conversion efficiency(PCE) of inverted polymer solar cells(PSCs)with only ZnO layer was quickly decreased from 2.7% to 2.2% when the thickness of ZnO layer was increased from 15 nm to 60 nm. However, the average PCE of inverted PSCs with ZnO layer modified with ILCNs only decreased from 3.5% to 3.4%, which is comparable to that of traditional PSCs with poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) anode buffer layer. The results suggested that the contact barrier between ZnO layer and poly(3-hexylthiophene) and phenyl-C61-butyric acid methylester(P3HT:PCBM)blended film compared to ZnO bulk resistance can more significantly influence the performance of inverted PSCs with sputtered ZnO layer. The vanishment of negative capacitive behavior of inverted PSCs with ILCNs modified ZnO layer indicated ILCNs can greatly decrease the contact barrier of ZnO/P3HT:PCBM interface.

Influence factors and mechanism of emission of ZnS:Cu nanocrystals

Copper-doped ZnS （ZnS：Cu） nanocrystals are synthesized by the sol-gel method. The average size of the ZnS：Cu nanocrystals is 3.1 nm. The x-ray diffraction indicates that increasing the Cu-dopant concentration results in a large shift in the diffraction angle. The effects of the dopant concentration, the reactant ratio, and aging temperature on the optical properties of the ZnS：Cu nanocrystals are also investigated. The fluorescence emission mechanism is analyzed by peak deconvolution using Gaussian functions. We find that the emission of the ZnS：Cu nanocrystal is composed of different luminescence centers at 430, 470, 490, 526, and 560 nm. The origins of these emissions are discussed and demonstrated by controlled experiments.

Magnetoelastic coupling effect of Fe10Co90 films grown on different flexible substrates

The magneto-mechanical coupling effect and magnetic anisotropy of Fe10Co90(FeCo)films deposited on silicon wafer(Si),flexible polyethylene terephthalate(PET),freestanding polydimethylsiloxane(PDMS),and pre-stretched 20%PDMS substrates were studied in detail.The loop squareness ratio Mr/Ms and the coercive Hc of the FeCo film grown on a PET substrate can be obviously tuned by applying a small tensile-bending strain,and those of the FeCo film grown on a freestanding PDMS substrate can only be slightly changed when applying a relatively large tensile bending strain.For the FeCo film prepared on a 20%pre-stretched PDMS,a wrinkled morphology is obtained after removing the pre-strain.The wrinkled FeCo film can keep the magnetic properties unchanged when applying a relatively large tensile bending strain perpendicular to the wrinkles.This reveals that PDMS is an ideal substrate for magnetic films to realize flexible immutability.Our results may help for developing flexible magnetic devices.

Plasmonics for solid-state lighting: enhanced excitation and directional emission of highly efficient light sources

Light sources based on reliable and energy-efficient light-emitting diodes (LEDs) are instrumental in the development of solid-statelighting (SSL). Most research efforts in SSL have focused on improving both the intrinsic quantum efficiency (QE) and the stability oflight emitters. For this reason, it is broadly accepted that with the advent of highly efficient (QE close to 1) and stable emitters, thefundamental research phase of SSL is coming to an end. In this study, we demonstrate a very large improvement in SSL emission (above70-fold directional enhancement for p-polarized emission and 60-fold enhancement for unpolarized emission) using nanophotonicstructures. This is attained by coupling emitters with very high QE to collective plasmonic resonances in periodic arrays of aluminumnanoantennas. Our results open a new path for fundamental and applied research in SSL in which plasmonic nanostructures are able tomold the spectral and angular distribution of the emission with unprecedented precision.

Cooperative interactions between nano-antennas in a high-Q cavity for unidirectional light sources

We analyse the resonant mode structure and local density of states in high-Q hybrid plasmonic-photonic resonators composed of dielectric microdisks hybridized with pairs of plasmon antennas that are systematically swept in position through the cavity mode.On the one hand,this system is a classical realization of the cooperative resonant dipole–dipole interaction through a cavity mode,as is evident through predicted and measured resonance linewidths and shifts.At the same time,our work introduces the notion of‘phased array’antenna physics into plasmonic-photonic resonators.We predict that one may construct large local density of states(LDOS)enhancements exceeding those given by a single antenna,which are‘chiral’in the sense of correlating with the unidirectional injection of fluorescence into the cavity.We report an experiment probing the resonances of silicon nitride microdisks decorated with aluminium antenna dimers.Measurements directly confirm the predicted cooperative effects of the coupled dipole antennas as a function of the antenna spacing on the hybrid mode quality factors and resonance conditions.

Room temperature preparation of highly stable cesium lead halide perovskite nanocrystals by ligand modification for white lightemitting diodes

The poor stability of halide perovskite nanocrystals(NCs)has severely hindered future practical application.Herein,we proposed a facile and effective ligand modification route to synthesize stable CsPbBr_(3) nanocrystals by introducing a double-terminal ligand,namely 4,4'-Azobis(4-cyanovalericacid)(CA),to replace the conventional oleic acid(OA)ligand at room temperature.The as-synthesized CsPbBr_(3)-CA not only possesses high photoluminescence quantum yield(72%)related to the reduced trap defects,but also shows significantly improved stability exposure to water,ethanol,light,and/or heat benefiting from the CA ligand anchored to NC surfaces tightly.The photoluminescence intensity of CsPbBr_(3)-CA maintains about 80%and 75%of its initial emission intensity after immersed in water or ethanol for 360 min,respectively,whereas that of the CsPbBr_(3)-OA was quenched completely within a few minutes.Moreover,an all-inorganic white light-emitting diode(LED)covered 126%National Television System Committee(NTSC)standard and 92%Rec.2020 standard was fabricated by combining the green CsPbBr_(3)-CA and commercial red-emitting K2SiF6:Mn4+(KSF)phosphors onto a blue LED chip.Thus,the presented work initiates the development of the room temperature preparation of high quality CsPbBr_(3) and shows prospect for next-generation displays.

Sonochemical synthesis of silver nanoparticles coated copper wire for low-temperature solid state bonding on silicon substrate

Silver nanoparticles (AgNPs) are directly grown on surface of ~25 μm copper wire by ultrasound-assisted chemical reduction. Silver nitrate is used as precursors, when polyvinylpyrrolidone (PVP) is added as a controller of the dimension of AgNPs. Influence of growth parameters such as precursor's concentration, ratio proportion of PVP and ultra-sonication on the growth of AgNPs coating are determined. The best morphology, size of the AgNPs are observed on copper wire. The results show that the copper wire coated with AgNPs of^100 nm diameter exhibits good antioxidation and ohmic contact after sinter on Si substrate at a temperature as low as 320℃, is especially suitable as a substitute for silver paste electrode used in silicon solar cells.

Highly efficient GaAs solar cells by limiting light emission angle

In a conventional flat plate solar cell under direct sunlight,light is received from the solar disk,but is re-emitted isotropically.This isotropic emission corresponds to a significant entropy increase in the solar cell,with a corresponding drop in efficiency.Here,using a detailed balance model,we show that limiting the emission angle of a high-quality GaAs solar cell is a feasible route to achieving power conversion efficiencies above 38%with a single junction.The highest efficiencies are predicted for a thin,light trapping cell with an ideal back reflector,though the scheme is robust to a non-ideal back reflector.Comparison with a conventional planar cell geometry illustrates that limiting emission angle in a light trapping geometry not only allows for much thinner cells,but also for significantly higher overall efficiencies with an excellent rear reflector.Finally,we present ray-tracing and detailed balance analysis of two angular coupler designs,show that significant efficiency improvements are possible with these couplers,and demonstrate initial fabrication of one coupler design.

Fabrication of highly efficient heterostructured Ag-CeO2/g-C3N4 hybrid photocatalyst with enhanced visible-light photocatalytic activity

On the basis of hydrothermal synthesis of Ag-CeO2 microspheres,Ag-CeO2/g-C3N4 composite photocatalyst with heterostructure was prepared by simple solvent evaporation of Ag-CeO2 and g-C3N4.To characterize the composition,structure,morphology and light absorption properties of the as-prepared Ag-CeO2/g-C3N4 composites,XRD,FTIR XPS,SEM,TEM,PL,BET and UV-vis DRS were used,respectively.The as-prepared photocatalyst was subjected to photocatalytic degradation of pollutants,and the prepared composite material has excellent photocatalytic activity for photodegradation of methylene blue(MB).The research shows that the photocatalytic properties of Ag-CeO2/g-C3N4 composites were related to the mass ratio of Ag-CeO2 microspheres and g-C3N4 nanosheets.When the ratio of Ag-CeO2 microspheres:g-C3N4 is 1:5,the composites have the highest photocatalytic activity,which was 9.6 and 3.3 times that of single Ag-CeO2 and g-C3N4,respectively.The improvement of photocatalytic activity is attributed to the heterostructure between the composite materials and the addition of noble metal silver,and the degradation of methylene blue by the visible light irradiation material is greatly improved.Finally,an attempt was made to analyze the principle of photocatalytic degradation of pollutants in prepared materials.