Semitransparent Layer Research Articles

A thin layer of Carbon Nano Tube (CNT) as semi-transparent charge collector that improve the performance of the GaAs Solar Cell

A novel use of carbon nanotube networks (CNT) as a semi-transparent layer for better charge collector in GaAs solar cells in order to improve the overall cell performance is presented. The different photovoltaic behaviors have been investigated considering substrate thickness, cell width, dependence between CNT work function and transmittance. CNT layer thickness is found to be optimized at 100nm for AM1.5G. The sheet resistivity is evaluated at 128Ω/□. The performance parameters of a cell with and without the CNT network are compared. The CNT networks allow for a greater area of charge collection on the surface of solar cells as well as serve as a lower resistance path for charge carriers with minimum voltage loss to travel to the top contact. This model thus significantly improves the power conversion efficiency from 26.04% to 29.18% under AM1.5G. The addition of a CNT layer was shown to minimize the voltage drop and maintain high maximum power levels at 34.4mW/cm2 for cells with larger width. EQE of the cell is well above 90%. The model has been validated with various reported experimental works. CNT layers with lower sheet resistance and better light transmission can therefore greatly improve the efficiency of solar cells.

Preparation of TiO2 paste starting from organic colloidal suspension for semi-transparent DSSC photo-anode application

We investigated the effect of different formulation strategies on the preparation of TiO2 screen printable pastes starting from the same organic colloidal suspension for dye-sensitized solar cells (DSSCs) application. As first strategy, we developed TiO2 pastes starting from nano-crystalline powder dried from the synthetized suspension, with and without an additional acid treatment, obtaining non-transparent scattering sintered layers. Instead, we demonstrate that starting from the sol solution is a key factor to obtain a well nano-dispersed TiO2 paste. The novel paste process resulted in a final homogeneous and semitransparent porous layer (T>80% @450–550nm). In order to evaluate the properties of TiO2 powders and inks we performed thermal analysis, BET and FTIR measurements. The films were screen printed on FTO (fluorinedoped tin oxide) glass and characterized after sintering via profilometry, FE-SEM analysis and UVVis spectra measurements. The photo-anode was further validated in small (2cm2) and large (90cm2) active area DSSCs, giving an average photovoltaic efficiency respectively of 5,22% and 2,39%, comparable with commercially available TiO2 paste with similar composition.

Nonstationary Heat Exchange and Stressed State in the Irradiated System of Layers with Different Transparencies

We pose the problem of investigation of the thermal stressed state in a system formed by infinite semitransparent and opaque heat-sensitive layers caused by the action of thermal radiation. On the basis of the obtained numerical solutions, we establish a series of new regularities of the influence of radiative heat exchange on the thermal and mechanical behavior of the system.

Blur Quantification of Medical Images: Dicom Media, Whole Slide Images, Generic Images and Videos

Introduction/ Background We have designed a quality assurance tool to quantify blur by quantifying the sharpness of custom-sized tiles composing an image, generating global results, detailed exchangeable logs and sharpness-maps regardless of their dimensions, quantity or acquisition rate [1]. We have now integrated the programming libraries and the standalone program we built to existing workflows and software, in order to improve quality assurance procedures. Aims When integrated in an acquisition workflow, the ability to map the quality of local areas inside an image allows to re-acquire parts of the image that were not scanned properly, or discard and re-acquire images when the global results fall under the thresholds set by the users. When integrated in an image analysis software, the regions of interest can be automatically chosen or suggested to the user according to the quality-map of the image to analyze, reducing the amount of incoherent analysis results. When integrated as a library in an image management platform, or as a standalone program in a storage server, a systematic quality check can detect de-calibration of the acquisition software, failed acquisitions that may be automatically deleted and users can be notified to re-acquire the images when below their quality-thresholds profiles. A quantified quality score can be inserted in each image’s metadata for traceability purposes. When integrated as a library in a local or remote image viewer, the best quality tiles can be sent first to the viewer, and magnification levels can be dynamically resampled for a better render. Methods One notable implementation, using our Java library, is inside the FlexMIm project [2], which includes 27 pathology laboratories in the Paris area (coordinated by APHP), research laboratories from University Paris 6 Paris 7, as well as 3 companies: TRIBVN, PERTIMM and Orange. All Whole Slide Images are systematically analyzed and mapped as they enter the platform. The focus map may be displayed on the web interface next to the thumbnail link to the WSI, or in the viewer as a semi-transparent layer over the WSI, or over the WSI map. During the test phase and first integrations in laboratories and hospitals as well as in the FlexMIm project, more than 5000 whole slide images of multiple formats (Hamamatsu NDPI, Aperio SVS, Mirax MRXS, JPEG2000 …) as well as hundreds of thousands of images of various formats (DICOM, TIFF, PNG, JPEG ...) and videos (H264) have been analyzed using our standalone software or our C, C++, Java and Python libraries. Using default or customizable thresholds’ profiles, WSI are sorted as “accepted”, “to review”, “to rescan”. In order to target the samples contained inside each WSI, special attention was paid to detecting blank tiles. Dynamic blank tile detection based on statistical analysis of each WSI was built and successfully validated for all our samples. Results More than 20 trillion pixels have been analyzed at a 3.5 billion pixels per quad-core processor per minute speed rate. Quantified results can be stored in JSON formatted logs or inside a MySQL or MongoDB database) or converted to any chosen data structure to be interoperable with existing software, each tile’s result being accessible in addition to the quality map and the global quality results. This solution is easily scalable as images can be stored at different locations, analysis can be distributed amongst local or remote servers, and quantified results can be stored in remote databases.

Thermal and electrical performance of an integrated PV-PCM system in double skin façades: A numerical study

In this article the performance of a system that integrates a photovoltaic (PV) layer and a phase change material (PCM) layer in a double skin façade (DSF) is investigated. A physical–mathematical model is developed to simulate the dynamic thermal behaviour of the system, and numerical simulations are carried out for different climates (Venice, Helsinki and Abu Dhabi) in order to evaluate the performance of the proposed solution. The numerical model combines different validated codes for the simulation of optical, thermal, and electrical behaviour of PCM, PV and DSF. The model is then coupled with the indoor air heat balance equation to evaluate the impact of the proposed façade system on the heating and cooling energy demand.The adoption of a PCM layer in the DSF cavity, in combination with a semi-transparent PV layer, leads to a reduction in the monthly cooling energy demand in the 20–30% range. This result is particularly relevant for hot climates – where cooling loads are seen throughout the year. The improvement in terms of heating load in more cold-dominated locations is limited. The smoothing of the PV module temperature leads to an increase in the electrical energy converted by the PV, with peak values of improvement in the range of 5–8% when the DSF is equipped with the PCM–PV configuration. Ventilation strategies of the façade cavity, coupled with the correct selection of PCM (and of its transition-phase temperature range), are the key aspects to ensure effective management of the proposed technology.

Study on array of photo-detector based absolute rotary encoder

Absolute rotary encoder is an electromechanical device which indicates the absolute position of an object. In this paper, a low cost absolute rotary encoder is presented. Proposed encoder measures the rotational position of a moveable object with accuracy of ±1° and resolution of 0.1°. Here, Encoder disc does not carry any binary or gray coded positional information, instead of that it acts as a positional pointer over the array of photo-detector based circular track. The one forth segment of fiber glass disc is kept transparent and rest portion is covered up by a semi-transparent layer. The disc is placed between the circular track and a light source. A marker at the centre of transparent portion indicates the angular position of the object. Now during the rotation of disc along with the object, high intensity of light is passed through the disc’s transparent portion compared to the semi-transparent portion and impinged over a fixed circular track. Thus according to the variation of light intensity over the track surface area, absolute angular position of object is determined by analyzing the variation of photo-detector’s output. In order to proof of this concept, an experimental prototype has been designed, developed and tested.

Quasi-monodispersed anatase TiO2 submicrospheres as current-contributed scattering particles for dye-sensitized solar cells

Hierarchical anatase TiO2 submicrospheres were synthesized by direct hydrothermal method at 120°C using Ti(SO4)2 and (NH4)2SO4 mixed solution as precursor. The calcined spheres in particle size of 150–200nm, which consisted of closely connected nanocrystals in a crystallite size of about 24.2nm and had a relatively high specific surface area of 43.2m2g−1 compared to microspheres. In presence of TiO2 submicrospheres as the scattering layer on top of semitransparent layer, the power conversion efficiency of dye-sensitized solar cells (DSSCs) was increased to as high as of 9.07% from 7.24%. This remarkable improvement compared to commercial scattering particles (efficiency of 8.33%) is mainly attributed to their higher surface area for increasing the loading of dye molecule as well as a lower resistance under 1 sun irradiation. The relationship between the conversion efficiency of DSSCs with interfacial resistance under 0.1 to 1.0 sun illumination was further investigated, the decrease of the light power density led to the increase of interfacial resistance. Moreover, even under 0.1 sun irradiation, DSSC still had an efficiency of 7.18% but a slightly lower Voc of 0.597V.

Semiconductor cylinder fiber laser

We fabricated a fiber laser that uses a thin semiconductor layer surrounding the glass core as the gain medium. This is a completely new type of laser. The In2Te3 semiconductor layer is about 15-nm thick. The fiber laser has a core diameter of 14.2 μm, an outside diameter of 126 μm, and it is 25-mm long. The laser mirrors consist of a thick vacuum-deposited aluminum layer at one end and a thin semitransparent aluminum layer deposited at the other end of the fiber. The laser is pumped from the side with either light from a halogen tungsten incandescent lamp or a blue light emitting diode flash light. Both the In2Te3 gain medium and the aluminum mirrors have a wide bandwidth. Therefore, the output spectrum consists of a pedestal from a wavelength of about 454 to 623 nm with several peaks. There is a main peak at 545 nm. The main peak has an amplitude of 16.5 dB above the noise level of −73 dB.

Materials and Photosensor Devices with High Radiation Stability

Semiconductor Hg3In2Te6 crystals and their analogous are solid solutions of In2Te3 and HgTe. Hg3In2Te6 crystals are congruently melted as chemical compound. Like In2Te3 the Hg3In2Te6 crystal has cubic crystal lattice with stoichiometric vacancies in their crystal structure. The electroconductivity, photoconductivity, mechanical, chemical properties of the crystals do not deteriorate after their irradiation by γ-photons with energies up to 1 MeV and doses up to 1018 cm-2 , by electrons with energies up to 300 MeV and doses up to 1019 cm-2 and by mixed reactor irradiation (filtered slow neutrons) with doses up to 1019 cm-2 [1,2]. This feature is determined by high concentration (~1021 cm-3) of stoihiometric vacancies (Vs) in crystal structure, where every third In-cation node is empty. These Vs are electroneutral, they capture all impurity atoms in these crystals and kept them in electroneutral state too. On the other hand this feature doesn't allow to form direct p-n junctions in these crystals by introducing the impurities. However, we have developed p-n junction analogues in form of Schottki diodes and corresponding photodiodes with semitransparent metal layer on single crystal Hg3In2Te6 substrate that allows irradiation to get into active region preserving this way all the advantages compared to p-n junction.

Design and fabrication of spectrally selective TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO tandem absorber for high-temperature solar thermal power applications

A new nanostructured TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO tandem absorber has been designed for high-temperature solar thermal power applications. The first three layers in this tandem act as an absorbing layer, whereas, TiAlSiCO and TiAlSiO act as semi-transparent and anti-reflecting layers. The tandem absorber was deposited on stainless steel substrates using a four-cathode reactive direct current unbalanced magnetron sputtering system. The composition and thicknesses of the individual component layers have been optimized by adjusting the reactive flow rate of C2H2, N2, O2, and also Al, Ti and Si target power densities to achieve high absorptance (0.961) and low emittance (0.07 at 82°C). The reflectance data showed that the absorptance increases gradually with shift of reflectance minimum to higher wavelengths from first layer to last layer (i.e., TiAlC to TiAlSiO). The thickness of optimized tandem absorber was calculated from the cross-sectional field-emission scanning electron microscopy images and confirmed using transmission electron microscopy. The performance evaluation of the tandem absorber has been evaluated by heating it in air and vacuum under cycling conditions at different temperatures. These results showed that the tandem absorber was stable up to 325°C in air for 400h and up to 650°C in vacuum for 100h, thus demonstrating its suitability for high-temperature solar thermal power generation applications.

Comparison of distributed vs. lumped series resistance modeling of thin-film solar cells and modules: Influence on the geometry-dependent efficiency

Limited lateral conductivities of the photo-active materials used in thin-film solar cells necessitate the use of semitransparent electrodes for current collection and lateral current transport. Due to the tradeoff between electrical conductivity and optical transmission, which should not underrun 80%, typical values for the sheet resistances of semitransparent electrodes deposited on glass amount to 10–20 Ω/sq. The power loss due to Joule heating and the accompanying voltage drop caused by this sheet resistance increases with cell length in current transport direction and thus, defines an upper limit for practical solar cell lengths. In the several approaches existing for calculation of the power loss, the semitransparent electrode layer is either modeled as one lumped resistance in series to the solar cell or as distributed resistance across the whole length of the solar cell in current transport direction. We present a quantitative comparison between these two conceptions to investigate the direct influence on the optimal solar cell geometry and to discuss the capabilities as well as limitations of each model. The computational study presented here is based on the material system PCDTBT:PC70BM (poly[N-9′-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] blended with phenyl-C70-butyric-acid-methyl-ester) for the photo-active layer and commonly used semitransparent conductive electrodes: ITO (indium doped tin-oxide) deposited on glass as well as on PET (polyethylene terephthalate) foil and highly doped PEDOT:PSS (poly(ethylene-dioxy-thiophene):poly(styrene-sulfonic acid)) named PH1000 on PET foil.

Simulation of the one-phase Stefan problem in a layer of a semitransparent medium

Radiative-conductive heat transfer in a semitransparent layer of a material with a phase transition is numerically simulated within the framework of solving the one-phase Stefan problem. Results of the solution describe the process of melting under equilibrium and nonequilibrium conditions of thermal energy supply. The possibility of simulation of thermal processes as applied to the development of both effective thermal protection and ideal technology of melting (evaporation) in layers of semitransparent materials is demonstrated.

Light-Emitting Diodes Fabricated From Carbon Ions Implanted Into p-Type Silicon

Silicon-based light-emitting diodes (LEDs) are fabricated using p-type silicon implanted with C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ions and postannealed at 1000 °C in flowing nitrogen. The ion implantation is carried out at ambient temperature (AT) and 400 °C to investigate the influence of high-temperature implantation on the luminescence of LEDs. Transmission electron microscopy shows a near-surface layer of amorphous silicon (a-Si) with nanoscale carbon-rich inclusions in both ambient and heated targets while an additional polycrystalline Si layer is observed in the heated target only. A Schottky diode is constructed from C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -implanted Si (C:Si) with a semitransparent gold layer on the implanted surface and aluminum on the back of the target. Contact firing at 400 °C in flowing nitrogen is used to optimize diode performance. Turn-ON voltage is determined to be about 3 V for all devices. Electroluminescence (EL) spectra show visible orange-red emission indicating luminescence primarily due to a-Si and Si nanoparticles in the LEDs fabricated from C:Si implanted at AT. The high-temperature samples produced EL attributed to a-Si and porous silicon carbide.

ITO-free large-area flexible organic solar cells with an embedded metal grid

We report on ITO-free large-area flexible organic solar cells with embedded thick metal grids. Embedded thick metal grids on flexible substrates allow uniform spin coating of thin layers of PEDOT:PSS (PH1000) semitransparent electrodes and organic semiconductor layers. A transparent SU8 photo-patternable polymer is used as a flexible substrate. Electroplated copper metallic grids, up to 15μm thick, defined by photolithography, produce a shadow area of 5.5% of the active area. Inverted solar cells with an active area of 9.3±0.2cm2, exhibited a fill factor of 0.53±0.06, and an open-circuit voltage of 808±5mV and a short-circuit current density of 5.5±0.5mA/cm2, yielding a power conversion efficiency of 2.4±0.4% under 100mW/cm2 air mass 1.5G illumination. The fill-factor and open circuit voltage values of large-area solar cells are comparable to values reported on small-area solar cells.

Characterization of buried metal-molecule-metal junctions using Fourier transform infrared microspectroscopy.

We have devised an infrared spectromicroscopy based experimental configuration to enable structural characterization of buried molecular junctions. Our design utilizes a small mercury drop at the focal point of an infrared microscope to act as a mirror in studying metal-molecule-metal (MmM) junctions. An organic molecular monolayer is formed either directly on the mercury drop or on a thin, infrared (IR) semi-transparent layer of Au deposited onto an IR transparent, undoped silicon substrate. Following the formation of the monolayer, films on either metal can be examined independently using specular reflection spectroscopy. Furthermore, by bringing together the two monolayers, a buried molecular bilayer within the MmM junction can be characterized. Independent examination of each half of the junction prior to junction formation also allows probing any structural and/or conformational changes that occur as a result of forming the bilayer. Because our approach allows assembling and disassembling microscopic junctions by forming and withdrawing Hg drops onto the monolayer covered metal, spatial mapping of junctions can be performed simply by translating the location of the derivatized silicon wafer. Finally, the applicability of this technique for the longer-term studies of changes in molecular structure in the presence of electrical bias is discussed.

A novel label-free colorimetric assay for DNA concentration in solution

Optical devices were fabricated by sandwiching a “monolithic” poly(N-isopropylacrylamide-co-N-(3-aminopropyl) methacrylamide hydrochloride) (pNIPAm-co-APMAH) microgel layer between two semitransparent Au layers. These devices, referred to as etalons, exhibit characteristic multipeak reflectance spectra, and the position of the peaks in the spectra primarily depends on the distance between the Au surfaces mediated by the microgel layer thickness. Here, we show that the positively charged microgel layer can collapse in the presence of negatively charged single stranded DNA (ssDNA) due to ssDNA induced microgel crosslinking. The collapse results in a change in the etalon's optical properties, which can be used to detect target DNA in a complex mixture.

Paradoxical effect of spatially homogenous transparent fields on simultaneous contrast illusions

In simultaneous brightness contrast (SBC) demonstrations, identical mid-luminance disks appear different from each other when one is placed on a black background while the other is placed on a white background. The strength of SBC effects can be enhanced by placing a semi-transparent layer on top of the display (Meyer's effect). Here, we try to separate the causes of Meyer's effect by placing a spatially homogenous transparent layer over a standard SBC display, and systematically varying the transmission level (alpha=0, clear; alpha=1, opaque) and color (black, gray, white) of the semi-transparent layer. Spatially homogenous transparent layers, which lack spatial cues, cannot be unambiguously interpreted as transparent fields. We measure SBC strength with both matching and ranking procedures. Paradoxically, with black layers, increasing alpha level weakens SBC when measured with a ranking procedure (no Meyer's effect) and strengthens SBC when measured with a matching procedure (Meyer's effect). With white and gray layers, neither procedure produces Meyer's effect. We account for the differences between white and black layers by positing that the visual system separates luminance from contrast. The results suggest that observers attend to different information in the matching and ranking procedures.

Spectral and Injection Level Dependence of Recombination Lifetimes in Silicon Measured by Impedance Spectroscopy

The effect of photo-generated carrier concentration on recombination lifetime is studied on silicon wafers using the impedance spectroscopy technique. The induced p <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^+$</tex></formula> -p-n structures are created by depositing semitransparent layers of high (Pd) and low (Al) work function (w.r.t silicon) metal layers on crystalline silicon (c-Si) wafers. The measurements are carried out by illuminating the device from the p <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^+$</tex></formula> -p side. The impedance data are analyzed by assuming a network consisting of a number of RC circuits, which, in turn, give recombination times (τ) controlled by defects in bulk and at the interfaces of the device. The maximum value of the effective recombination lifetime (τ) is found to be 12.3 ± 0.4 μs at an intensity of ∼100 mW/cm <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^2$</tex></formula> , which matches closely with the maximum value 11.4 ± 1.0 μs obtained under forward bias (+ 0.4 V) conditions in the same sample in the dark. These values match well with the effective minority carrier lifetime obtained using the microwave photoconductive decay technique on the same silicon wafer prior to device fabrication.

Identification of concealed materials, including explosives, by terahertz reflection spectroscopy

We report on a method for extracting the characteristic features of covered materials, including hexogen, in the range from 0.5 to 1.8 THz. This time-domain spectroscopy-based technique takes into account only part of the signal reflected from a covered sample and analyzes it by using the Fourier transform. The obtained power spectrum has distinctive peaks that correspond to peaks measured in the transmission configuration and can be used for further identification of the materials. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduc- tion of this work in whole or in part requires full attribution of the original publication, including its DOI. (DOI: 10.1117/1.OE.53.3.031202) spectral dynamics analysis method for identification of explosives in the reflection regime. In this article, we propose a new signal processing method to reveal characteristic THz fingerprints of materials covered with semitransparent layers such as a sheet of polyethylene or paper in the range of about 0.5 to 1.8 THz. The method takes into account the only part of the signal reflected from the covered sample that is then analyzed in the frequency domain with the Fourier transform. The obtained spectrum has very distinctive peaks that correspond to the main peaks measured in the transmission configuration, and this obtained spectrum is what in turn makes reliable identifica- tion possible.

Dynamic Modeling of a Solar Reactor for Zinc Oxide Thermal Dissociation and Experimental Validation Using IR Thermography

A dynamic numerical model of a solar cavity-type reactor for the thermal dissociation of ZnO is formulated based on a detailed radiative heat transfer analysis combining the Monte Carlo ray-tracing technique and the radiosity enclosure theory. The quartz window is treated as a semitransparent glass layer with spectrally and directionally dependent optical properties. Model validation is accomplished by comparison with experimental results obtained with a 10-kW solar reactor prototype in terms of cavity temperatures, reaction extents, and quartz window temperature distribution measured by IR thermography. The solar-to-fuel energy conversion efficiencies obtained experimentally are reported, and the various energy flows are quantified.