Development and Fabrication of a Multi-Layer Planar Solar Light Absorber Achieving High Absorptivity and Ultra-Wideband Response from Visible Light to Infrared.

The objective of this study is to create a planar solar light absorber that exhibits exceptional absorption characteristics spanning from visible light to infrared across an ultra-wide spectral range. The eight layered structures of the absorber, from top to bottom, consisted of Al2O3, Ti, Al2O3, Ti, Al2O3, Ni, Al2O3, and Al. The COMSOL Multiphysics® simulation software (version 6.0) was utilized to construct the absorber model and perform simulation analyses. The first significant finding of this study is that as compared to absorbers featuring seven-layered structures (excluding the top Al2O3 layer) or using TiO2 or SiO2 layers as substituted for Al2O3 layer, the presence of the top Al2O3 layer demonstrated superior anti-reflection properties. Another noteworthy finding was that the top Al2O3 layer provided better impedance matching compared to scenarios where it was absent or replaced with TiO2 or SiO2 layers, enhancing the absorber's overall efficiency. Consequently, across the ultra-wideband spectrum spanning 350 to 1970 nm, the average absorptivity reached an impressive 96.76%. One significant novelty of this study was the utilization of various top-layer materials to assess the absorption and reflection spectra, along with the optical-impedance-matching properties of the designed absorber. Another notable contribution was the successful implementation of evaporation techniques for depositing and manufacturing this optimized absorber. A further innovation involved the use of transmission electron microscopy to observe the thickness of each deposition layer. Subsequently, the simulated and calculated absorption spectra of solar energy across the AM1.5 spectrum for both the designed and fabricated absorbers were compared, demonstrating a match between the measured and simulated results.

Comparison of the Degradation Effect of Methylene Blue for ZnO Nanorods Synthesized on Silicon and Indium Tin Oxide Substrates.

In the context of ZnO nanorods (NRs) grown on Si and indium tin oxide (ITO) substrates, this study aimed to compare their degradation effect on methylene blue (MB) at different concentrations. The synthesis process was carried out at a temperature of 100 °C for 3 h. After the synthesis of ZnO NRs, their crystallization was analyzed using X-ray diffraction (XRD) patterns. The XRD patterns and top-view SEM observations demonstrate variations in synthesized ZnO NRs when different substrates were used. Furthermore, cross-sectional observations reveal that ZnO NRs synthesized on an ITO substrate exhibited a slower growth rate compared to those synthesized on a Si substrate. The as-grown ZnO NRs synthesized on the Si and ITO substrates exhibited average diameters of 110 ± 40 nm and 120 ± 32 nm and average lengths of 1210 ± 55 nm and 960 ± 58 nm, respectively. The reasons behind this discrepancy are investigated and discussed. Finally, synthesized ZnO NRs on both substrates were utilized to assess their degradation effect on methylene blue (MB). Photoluminescence spectra and X-ray photoelectron spectroscopy were employed to analyze the quantities of various defects of synthesized ZnO NRs. The effect of MB degradation after 325 nm UV irradiation for different durations can be evaluated using the Beer-Lambert law, specifically by analyzing the 665 nm peak in the transmittance spectrum of MB solutions with different concentrations. Our findings reveal that ZnO NRs synthesized on an ITO substrate exhibited a higher degradation effect on MB, with a rate of 59.5%, compared to NRs synthesized on a Si substrate, which had a rate of 73.7%. The reasons behind this outcome, elucidating the factors contributing to the enhanced degradation effect are discussed and proposed.

Special Issue on Clinical Medicine for Healthcare and Sustainability.

Recently, due to the advancement of network technology, big data and artificial intelligence, the healthcare industry has undergone many sector-wide changes. Medical care has not only changed from passive and hospital-centric to preventative and personalized, but also from disease-centric to health-centric. Healthcare systems and basic medical research are becoming more intelligent and being implemented in biomedical engineering. This Special Issue on "Clinical Medicine for Healthcare and Sustainability" selected 30 excellent papers from 160 papers presented in IEEE ECBIOS 2019 on the topic of clinical medicine for healthcare and sustainability. Our purpose is to encourage scientists to propose their experiments and theoretical researches to facilitate the scientific prediction and influential assessment of global change and development.

Selected Papers from 2019 IEEE Eurasia Conference on Biomedical Engineering, Healthcare and Sustainability (IEEE ECBIOS 2019).

Recently, healthcare has undergone a sector-wide transformation thanks to advances in computing, networking technologies, big data, and artificial intelligence. Healthcare is not only changing from being reactive and hospital-centered to preventive and personalized, but it is also changing from being disease focused to well-being centered. Healthcare systems, as well as fundamental medicine research, are becoming smarter and enabled in biomedical engineering. This special issue on "Selected Papers from 2019 IEEE Eurasia Conference on Biomedical Engineering, Healthcare, and Sustainability (IEEE ECBIOS 2019)" selected nine excellent papers from 160 papers presented at IEEE ECBIOS 2019 on the topics of environmental health sciences and public health. Our aim is to encourage scientists to publish their experimental and theoretical research to promote scientific predictions and impact assessments of global change and development.

Self-Etching-Induced Morphological Evolution of ZnO Microrods Grown on FTO Glass by Hydrothermal Method.

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; CH3(CH2)17Si(OCH3)3). 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.

Improved Color Purity of Blue Organic Light-Emitting Diodes with Double Hole-Transporting Structure.

A blue organic light-emitting diode with a double hole-transporting (DHT) structure has been developed. The device, ITO/N,N'-Bis (naphthalene-1-yl)-N,N'-bis(phenyl)-benzidine/4,4'-Bis (N-carbazolyl)-1,1'-biphenyl (CBP)/4,4'-Bis(2,2-diphenylethen-yl) diphenyl/CBP/tris(8-hydroxyquinolate)aluminum/lithium fluoride/aluminum, consists of a hole-transporting layer, a DHT structure layer and an electron-transporting layer. The blue color purity is improved by modulation the thickness of CBP layer. When the thicknesses of left CBP and right CBP are respectively 8 nm and 2 nm, the more pure blue coordinates (0.155, 0.079) are obtained at 9 V, which are very close to the national television system committee standard blue coordinate (0.14, 0.08). Furthermore the current density, brightness and the luminous efficiency of device with the left CBP of 8 nm and the right CBP of 2 nm are respectively 144.7 mA/cm2, 1065 cd/m2 and 0.93 cd/A at voltage of 9 V.

Optimization of the dye-sensitized solar cell performance by mechanical compression.

In this study, the P25 titanium dioxide (TiO2) nanoparticle (NP) thin film was coated on the fluorine-doped tin oxide (FTO) glass substrate by a doctor blade method. The film then compressed mechanically to be the photoanode of dye-sensitized solar cells (DSSCs). Various compression pressures on TiO2 NP film were tested to optimize the performance of DSSCs. The mechanical compression reduces TiO2 inter-particle distance improving the electron transport efficiency. The UV-vis spectrophotometer and electrochemical impedance spectroscopy (EIS) were employed to quantify the light-harvesting efficiency and the charge transport impedance at various interfaces in DSSC, respectively. The incident photon-to-current conversion efficiency was also monitored. The results show that when the DSSC fabricated by the TiO2 NP thin film compressed at pressure of 279 kg/cm(2), the minimum resistance of 9.38 Ω at dye/TiO2 NP/electrolyte interfaces, the maximum short-circuit photocurrent density of 15.11 mA/cm(2), and the photoelectric conversion efficiency of 5.94% were observed. Compared to the DSSC fabricated by the non-compression of TiO2 NP thin film, the overall conversion efficiency is improved over 19.5%. The study proves that under suitable compression pressure the performance of DSSC can be optimized.

Characterization of photovoltaics with In2S3 nanoflakes/p-Si heterojunction.

We demonstrate that heterojunction photovoltaics based on hydrothermal-grown In2S3 on p-Si were fabricated and characterized in the paper. An n-type In2S3 nanoflake-based film with unique 'cross-linked network' structure was grown on the prepared p-type silicon substrate. It was found that the bandgap energy of such In2S3 film is 2.5 eV by optical absorption spectra. This unique nanostructure significantly enhances the surface area of the In2S3 films, leading to obtain lower reflectance spectra as the thickness of In2S3 film was increased. Additionally, such a nanostructure resulted in a closer spacing between the cross-linked In2S3 nanostructures and formed more direct conduction paths for electron transportation. Thus, the short-circuit current density (Jsc) was effectively improved by using a suitable thickness of In2S3. The power conversion efficiency (PCE, η) of the AZO/In2S3/textured p-Si heterojunction solar cell with 100-nm-thick In2S3 film was 2.39%.

Effect of compressed TiO2 nanoparticle thin film thickness on the performance of dye-sensitized solar cells.

In this study, dye-sensitized solar cells (DSSCs) were fabricated using nanocrystalline titanium dioxide (TiO2) nanoparticles as photoanode. Photoanode thin films were prepared by doctor blading method with 420 kg/cm2 of mechanical compression process and heat treatment in the air at 500°C for 30 min. The optimal thickness of the TiO2 NP photoanode is 26.6 µm with an efficiency of 9.01% under AM 1.5G illumination at 100 mW/cm2. 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.

Annealing effect and photovoltaic properties of nano-ZnS/textured p-Si heterojunction.

The preparation and characterization of heterojunction solar cell with ZnS nanocrystals synthesized by chemical bath deposition method were studied in this work. The ZnS nanocrystals were characterized by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Lower reflectance spectra were found as the annealing temperature of ZnS film increased on the textured p-Si substrate. It was found that the power conversion efficiency (PCE) of the AZO/ZnS/textured p-Si heterojunction solar cell with an annealing temperature of 250°C was η = 3.66%.

Surface plasma resonant effect of gold nanoparticles on the photoelectrodes of dye-sensitized solar cells.

In this study, we prepared different shapes of gold nanoparticles by seed-mediated growth method and applied them on the photoelectrodes of dye-sensitized solar cells (DSSCs) to study the surface plasma resonant (SPR) effect of gold nanoparticles on the photoelectrodes of dye-sensitized solar cells. The analyses of field emission scanning electron microscopy show that the average diameter of the spherical gold nanoparticles is 45 nm, the average length and width of the short gold nanorods were 55 and 22 nm, respectively, and the average length and width of the long gold nanorods were 55 and 14 nm, respectively. The aspect ratio of the short and long gold nanorods was about 2.5 and 4, respectively. The results of ultraviolet-visible absorption spectra show that the absorption wavelength is about 540 nm for spherical gold nanoparticles, and the absorption of the gold nanorods reveals two peaks. One is about 510 to 520 nm, and the other is about 670 and 710 nm for the short and long gold nanorods, respectively. The best conversion efficiency of the dye-sensitized solar cells with spherical gold nanoparticles and short and long gold nanorods added in is 6.77%, 7.08%, and 7.29%, respectively, and is higher than that of the cells without gold nanoparticles, which is 6.21%. This result indicates that the effect of gold nanoparticles on the photoelectrodes can increase the conductivity and reduce the recombination of charges in the photoelectrodes, resulting in the increase of conversion efficiency for DSSCs. In addition, the long gold nanorods have stronger SPR effect than the spherical gold nanoparticles and short gold nanorods at long wavelength. This may be the reason for the higher conversion efficiency of DSSCs with long gold nanorods than those of the cells with spherical gold nanoparticles and short gold nanorods.

n-ZnO nanorods/p+-Si (111) heterojunction light emitting diodes.

In this study, we report the effects of thermal annealing in nitrogen ambient on the optical and electrical properties of zinc oxide (ZnO) nanorod (NR) arrays for the application in light emission diodes (LED). The single-crystalline ZnO NR array was synthesized on p+-Si (111) substrate without seed layer using simple, low-cost, and low-temperature hydrothermal method. The substrate surface was functionalized by hydrofluoric acid and self-assembled monolayer of octadecyltrimethoxysilane ((CH3 (CH2)17Si(OCH3)3). ZnO NRs were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and micro-photoluminescence (micro-PL). The results of FESEM and XRD indicate that single crystalline ZnO NRs with (002) preferred orientation along the substrate surface is successfully grown on functionalized p+-Si (111) substrate. The current-voltage and electroluminescence (EL) characteristics of the LED show that the most suitable annealing temperature ranges from 400°C to 600°C. Both PL and EL spectra show broadband emissions, ultraviolet and visible (green-yellow) light. The white-like light emission is able to be observed by naked eyes.

Effect of TiO2 nanotubes with TiCl4 treatment on the photoelectrode of dye-sensitized solar cells.

In this study, we used the electrochemical anodization to prepare TiO2 nanotube arrays and applied them on the photoelectrode of dye-sensitized solar cells. In the field emission scanning electron microscopy analysis, the lengths of TiO2 nanotube arrays prepared by electrochemical anodization can be obtained with approximately 10 to 30 µm. After titanium tetrachloride (TiCl4) treatment, the walls of TiO2 nanotubes were coated with TiO2 nanoparticles. XRD patterns showed that the oxygen-annealed TiO2 nanotubes have a better anatase phase. The conversion efficiency with different lengths of TiO2 nanotube photoelectrodes is 3.21%, 4.35%, and 4.34% with 10, 20, and 30 µm, respectively. After TiCl4 treatment, the efficiency of TiO2 nanotube photoelectrode for dye-sensitized solar cell can be improved up to 6.58%. In the analysis of electrochemical impedance spectroscopy, the value of Rk (charge transfer resistance related to recombination of electrons) decreases from 26.1 to 17.4 Ω when TiO2 nanotubes were treated with TiCl4. These results indicate that TiO2 nanotubes treated with TiCl4 can increase the surface area of TiO2 nanotubes, resulting in the increase of dye adsorption and have great help for the increase of the conversion efficiency of DSSCs.

Investigation of hole transport layer in relation to the properties of organic solar cells.

Organic solar cells based on a blend of copper phthalocyanine and bulk fullerene are fabricated with a double hole transport layer system. The double hole transport layer was composed of poly3,4-ethylenedioxythiophene:polystyrenesulfonate, and copper phthalocyanine and inserted between the anode and active layer. The double hole transport layer system utilizes advantages of both layer. The poly3,4-ethylenedioxythiophene:polystyrenesulfonate layer modifies the surface morphology of the ITO anode and the copper phthalocyanine layer enhances hole transport. In order to enhance the conductivity of the modification layer, the optimal amount of glycerol is doped into poly3,4-ethylenedioxythiophene:polystyrenesulfonate. Furthermore, the photovoltaic characteristics are further improved. Insertion of the double hole transport layer with a 4 nm-thick copper phthalocyanine layer resulted in open circuit voltage, short current, and power conversion efficiency as high as 0.46 V, 8.8 mA/cm2 and 1.37%, respectively.

ZnO thin film with nanorod arrays applied to fluid sensor.

A ZnO guiding layer with nanorod arrays grown on a 90°-rotated ST-cut (42°45) quartz substrate was used to fabricate a Love wave fluid sensor. ZnO nanorod arrays synthesized on the guiding layer enhance the sensitivity of the flow rate. ZnO thin films were deposited by radio frequency magnetron sputtering and ZnO nanorod arrays were then synthesized on the thin films via the hydrothermal method. The crystalline structure and surface morphology of ZnO thin films and nanorod arrays were examined by X-ray diffraction and scanning electron microscopy. The effects of the thickness of ZnO thin film and the surface morphology of ZnO nanorod arrays on the sensitivity of flow rate were investigated. A linear response between flow rate and the return loss of the sensor with one-port resonator type can be obtained by adjusting the thickness of ZnO thin film and the length of nanorod arrays.

Synthesis and characterization of gold nanodogbones by the seeded mediated growth method.

Novel gold nanodogbones (GDBs) are successfully fabricated using a simple seeded mediated growth (SMG) method. The shapes of GDBs depend on the amount of added vitamin C solvent. The amount of vitamin C solvent was varied from 10 to 40 µl to investigate the influence of vitamin C solvent on the GDBs. It is found that the aspect ratios (R) of GDBs were in the range from 2.34 to 1.46, and the UV-vis absorption measurement revealed a pronounced blueshift on the longitudinal surface plasmon resonance (SPR) band from 713 to 676 nm. The GDBs were determined by x-ray diffraction (XRD) to be single-crystalline with a face-centered cubic (fcc) structure. The lattice constant calculated from this selected-area electron diffraction (SAED) pattern is 4.068 Å.