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Owing to its contribution to carbon emission reduction, green energy has received widespread attention. Among green energy sources, solar energy is regarded as the most important. In solar energy production, dye-sensitized solar cells (DSSCs) have been favored owing to their characteristics of simple manufacturing and high efficiency as a third-generation solar cell technology. DSSCs are prospective candidates for powering indoor Internet of Things (IoT) devices. In this study, to find a method to enhance DSSCs' efficiency, the advantages and disadvantages of the screen printing method and the mechanical pressing and annealing method were analyzed. Using an improved method, a TiO2 photoanode was processed and annealed, and the DSSCs with the photoanode showed an efficiency increase from 1.10 to 4.78%. [ABSTRACT FROM AUTHOR]

A simple and low-cost fabrication method of dye-sensitized solar cells (DSSCs) was developed to improve the structure and performance of the photoanode with the pressed layer and compact TiO2 thin film using spin coating, screen printing, and mechanical compression. In this study, four different TiO2 layers were adopted to fabricate photoanodes: a mesoporous TiO2 nanoparticles (NPs) layer, a pressed TiO2 NPs layer, a mesoporous TiO2 NPs layer on the TiO2 compact thin film, and a pressed TiO2 NPs layer on the TiO2 compact thin film. The compact thin film was deposited on the fluorine-doped tin oxide (FTO) glass via spin coating, while the mesoporous TiO2 NPs layer was deposited via the screen-printing method. The pressed TiO2 NPs layer was produced by compressing the mesoporous TiO2 NPs layer with a hydraulic press machine. When using the pressed TiO2 NPs layer for the photoanode of DSSC, the power conversion efficiency of DSSC was enhanced the most. The electron lifetime for DSSC with photoanodes based on the pressed TiO2 NPs and mesoporous TiO2 NPs layers were 8.217 and 6.287 ms, respectively. The power conversion efficiency of DSSC with photoanodes based on the pressed TiO2 NPs layer was 5.4%, while that based on the mesoporous TiO2 NPs layer was 4.08%. DSSC with photoanodes based on the pressed TiO2 NPs layer showed a significant increase in the power conversion efficiency by 36.16% compared to that based on the mesoporous TiO2 NPs layer. [ABSTRACT FROM AUTHOR]

The doctor blade coating method is used to prepare dye-sensitized solar cells (DSSCs) and dope the original titanium dioxide (TiO2, P25) photoanode (PA) with single-layer graphene (G), graphene quantum dots (GQDs), and gold (Au) nanoparticles in this research. The results show that doping PAs with G, GQDS, and Au effectively increases the short-circuit current density ( J sc ) , conversion efficiency (η), and decreases the internal structure impedance ( R k ) of DSSCs. J sc increases from 13.62 to 17.02, 15.22, 16.05 mA/cm2, while η (%) increases from 6.36 to 7.50, 7.08, 7.04% when doping G, GQDs, and Au, respectively. The analysis of Electrochemical Impedance Spectroscopy (EIS) reveals that the doping decreases R k from 11.28 to 8.36, 8.78, 8.54 Ω , respectively. Then, the titanium dioxide (TiO 2) -doped G-GQDs, G-Au, and QDs-Au on DSSCs influence J sc that increases to 5.45, 15.37, and 15.31 mA/cm2, respectively. In this case, the values of η are found to be 7.21%, 7.35%, and 7.00%, while those of R k are 8.44, 8.63, and 9.18 Ω. The values of J sc and η are highest but that of R k are lowest when doping with G, which proves that the photoanode of the DSSC effectively activates the photogenerated electrons in the film by doping single-layer graphene and TiO2 captures its electrons through graphene. The decreasing electron–hole recombination rate allows the photogenerated electrons to be quickly transferred to the external circuit. As a result, the efficiency of DSSCs is improved. [ABSTRACT FROM AUTHOR]

This study explores the influence of molar ratio of the synthetic solution of methylammonium iodide (MAI) and PbI2 on perovskite solar cells. The complete perovskite crystals must be produced in a low-humidity environment. The substrate is spin-coated in the adjusted MAPbI3 synthesis solution and annealed by using a nitrogen furnace tube to form perovskite crystals. During the crystallization of MAPbI3, some of the PbI2 remains, which improves the efficiency of the perovskite solar cell. Therefore, we adjust the molar concentration of MAI to find the appropriate amount of the PbI2 residual. We fix the MAI molar concentration at 1 M and adjust the PbI2 molar concentration from 0.8 M to 1.4 M. The molar ratios of MAI and PbI2 are, then, 1:0.8, 1:1, 1:1.2, and 1:1.4, respectively. Then, we use UV–vis, FE-SEM, and photoelectric conversion efficiency (PCE) measurements for comparing the growth of perovskite crystals and their photoelectric characteristics. The results show that 1.2 M of PbI2 is the most appropriate concentration for perovskite solar cells among the adjusted concentrations. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) nanorod based gas sensor was successfully fabricated with interdigital electrode on silicon substrate. The highest sensitivity value is 5.24 at 600 ppm CO2 gas ambient. The influence of growth temperature of ZnO ranging from 90 to 190 °C by the high temperature hydrothermal method was investigated. The ZnO nanorod array were characterized by using field emission scanning electron microscopy (FE-SEM), photoluminescence spectroscopy, X-ray diffraction pattern. From FE-SEM results, the morphology of ZnO nanorods changes from hexagonal structure to sponge-like shape as the growth temperature increases. When the growth temperature is below 150 °C, hexagonal nanorod growth is observed. On the other hand, when the growth temperature is above 170 °C sheet growth is found. In the gas sensor measurements, it is found that ZnO nanorod grown at 150 °C has the best gas sensing performance due to its least intrinsic defects in this study. [ABSTRACT FROM AUTHOR]

In this research, the zinc oxide (ZnO) microrods were grown by hydrothermal method on fluorine-doped tin oxide (FTO) glass functionalized by self-assembled monolayer of octadecyltrimethoxysilane (ODS; CH(CH)Si(OCH)). The sharp-tip or polygonal shape with specific facets at the top end of ZnO microrods can be obtained by post retention at low temperature. The morphologies were characterized by the field-emission scanning electron microscope (FESEM) and transmission electron microscopy (TEM). The results confirm that the morphology change at the top end is due to self-etching. The mechanism responsible for the formation of various top-end morphologies was proposed. The specific facets that left after 6-h retention were identified. The room-temperature micro-photoluminescence spectra showed a strong ultraviolet emission at 387 nm, and a broad emission at a range of from 500 to 700 nm. The morphology change also influences the photoluminescence (PL) spectra. A satellite peak in the UV emission spectra was observed. The peak may be attributed to the morphology effect of the microrods. [ABSTRACT FROM AUTHOR]

A method to control the vortex state (flux-closure state) nucleation and annihilation field in asymmetric permalloy (Py) rings is presented. By introducing an inner circle shifted from the center of outer circle by a shift length, samples of asymmetric permalloy rings with different asymmetric ratios were fabricated by using E-beam lithography, sputtering, lift-off techniques, and measured by focused magneto-optic Kerr effect magnetometry. The vortex nucleation (Hn) and vortex annihilation (Han) fields, analyzed from the simulated and experimental hysteresis loops of 500 nm and 1000 nm outer diameters, have linear relations to the asymmetric ratio. When the lateral size reduces down to nanosize, two switching behaviors for the simulated hysteresis loops were observed. The single switching loop indicates that the switching process is single-domain switching and the all the spins rotate coherently. The double switching loop corresponds to the switching process via the formation of a vortex state. Both analyzed switching fields from the experiment and simulation present a linear relation with the aspect ratio in the small range of variation. This relation indicates that the Hn and Han of asymmetric ring arrays are mainly controlled by the shape anisotropy. It is observed that the switching behavior is in agreement with the experimental results. [ABSTRACT FROM PUBLISHER]

In this study, dye-sensitized solar cells (DSSCs) were fabricated using nanocrystalline titanium dioxide (TiO 2) nanoparticles as photoanode. Photoanode thin films were prepared by doctor blading method with 420 kg/cm 2 of mechanical compression process and heat treatment in the air at 500°C for 30 min. The optimal thickness of the TiO 2 NP photoanode is 26.6 μm with an efficiency of 9.01% under AM 1.5G illumination at 100 mW/cm 2. The efficiency is around two times higher than that of conventional DSSCs with an uncompressed photoanode. The open-circuit voltage of DSSCs decreases as the thickness increases. One DSSC (sample D) has the highest conversion efficiency while it has the maximum short-circuit current density. The results indicate that the short-circuit current density is a compromise between two conflict factors: enlargement of the surface area by increasing photoanode thickness and extension of the electron diffusion length to the electrode as the thickness increases. [ABSTRACT FROM AUTHOR]

In this study, a metal-oxide-semiconductor (MOS) structure with NiSi2nanocrystals embedded in a high-κ oxide layer, HfO2, was fabricated. The vertical transport properties have been studied by the temperature-dependent current-gate voltage (I-Vg) measurement. The temperature-dependent I-Vgcurves show another threshold voltage of between about −3.7 and −3.2 V in the forward and backward sweeps of the low temperature region, from 30 K to 150 K. We attribute this abnormal threshold voltage to charge redistribution due to the resistant phase change of the NiSi2nanocrystals. [ABSTRACT FROM PUBLISHER]

The domain wall motion in permalloy nanowires has been investigated widely due to its potential for a new type of memory. In this paper. we use the LLG Simulator based on the Landau-Lifshitz-Gilbert (LLG) equation to investigate the field-driven domain-wall motion in a long, straight ferromagnetic strip. An injection field of 60 Oe is applied to inject a domain wall from an extended disk into the nanowire. We found a dependence of nanowire dimensions with the velocity of domain wall. By increasing the width of the nanowire, the velocity of the domain wall motion also increases, while the Walker breakdown field (HWB) decreases. On the other hand, increasing the thicknesses of the nanowire, the domain wall velocity, HWB, and demagnetizing field all decrease. By applying a vertical field from 0 to 1000 Oe in order to enhance the demagnetizing field, it is found the HWB is increased from 16  to 20 Oe. [ABSTRACT FROM PUBLISHER]

Pinning phenomena were investigated in the superconducting Nb thin film with composite hexagonal arrays. The composite pinning arrays were consisting of two kinds of pinning sites with different pinning sizes. The smaller pinning defects were added to the center of every honeycomb pinning array to observe the configuration of the vortices, comparing to the periodic triangular and honeycomb arrays. The film with this kind of composite array can be regarded as a transition between the films with triangular array and honeycomb array. The critical current as a function of magnetic field for four samples were measured. Regular 150 Oe interval of the matching fields for the triangular arrays was found, while for the honeycomb arrays, the interstitial vortices were caged at the center of every honeycomb array, causing 50 Oe interval of the matching fields. For the samples with composite arrays, the 100 Oe or 50 Oe intervals of matching fields correspond to every larger or smaller pinning site capturing one more vortex, respectively. We found that the relative pinning strength of the large pinning sites is greater than that of the small ones. We conducted the simulations based on the time dependent Ginzburg-Landau theory to confirm that the interstitial vortices did exist in the honeycomb arrays which caused the various intervals between the matching fields. [ABSTRACT FROM AUTHOR]

A method to determine the relative pinning strength of different pinning sites in composite hexagonal pinning arrays is proposed and experimentally realized. Six different samples of superconducting Nb films with composite hexagonal arrays were fabricated and measured. Two types of pinning sites have different sizes. The density of one type of pinning site is twice that of the other. The critical current versus the applied magnetic fields were also measured. The vortex configurations at the matching fields can be deduced from these curves and verified by molecular dynamic simulations. The relative pinning strength of different pinning sites can be determined from these configurations. The method could be extended to decide the optimal pinning size or to compare the pinning strength of pinning sites made of different materials. [ABSTRACT FROM AUTHOR]

A study was made of the exchange bias effect in a structure of SiO2/Ta (5 nm)/NiFe (7 nm)/IrMn (10 nm)/CoFeB (7 nm)/Ta (5 nm) with nanoscale antidot arrays. The nanostructure comprised rhomboid lattice antidot arrays with antidot diameters from 150 to 300 nm and a rhomboid lattice period of 500 nm. Enhancements of exchange bias HEX and coercivity HC were observed in the nanostructure antidot arrays compared to continuous film. These effects were mainly ascribed to the physical limitations on ferromagnetic and antiferromagnetic layers due to the presence of antidots. In antidot arrays, due to the presence of nonmagnetic holes, the ferromagnetic–ferromagnetic interactions in FM layer are reduced, leading to smaller ferromagnetic domains and larger exchange bias with the random-field model. In this paper, the relation between the antidot diameter size and exchange bias was studied. [ABSTRACT FROM AUTHOR]