Pyramid Height Research Articles

FEM and experimental studies of flexible pressure sensors with micro-structured dielectric layers

E-skin (electronic skin) is a key component for use ranging from wearable electronic devices to human-machine interactions. Previous studies proposed that a parallel plate capacitor with a PDMS dielectric layer of micro-pyramids showed good pressure sensing abilities, but overlooked effects of the flat PDMS layers at the top and bottom of these microstructures induced by fabrication processes of soft imprinting. In this work, these effects were firstly studied by the finite element method. The second-order Ogden model was employed to describe the nonlinear mechanical behaviors of the PDMS. We found that the E-skin sensing unit showed increased sensitivity but decreased linearity with the increase of the pyramid height ratio. 48% pyramid height ratio was therefore applied for experimental studies for compromising the performances. We demonstrated an easy accessible and cost-effective method of fabricating the sensing unit, by using a commercial precision abrasive sheet as the mold of the microstructured dielectric film. We introduced a prefilling step to control the pyramid height ratio. Experimental results proved that the sensitivity, pressure resolution and time response of the sensor unit with pyramid height ratio of 45% were better than that with 0. We further demonstrated its applications as a wearable health monitoring device and an approaching and touch sensing unit for a 3D-printed soft hand, showing its great potentials in continuous health monitoring sensors, as well as large area human-machine interactions.

Influence of small size pyramid texturing on contact shading loss and performance analysis of Ag-screen printed mono crystalline silicon solar cells

Front side textured random pyramids are widely utilized in major industries for the performance enhancement of crystalline silicon (c-Si) solar cells. Random pyramids not only reduce the surface reflectance but also improve the light trapping effect. Therefore, it is necessary to understand the pyramid height affecting the cell performance, further improving cell efficiency. In this work, we present an experimental study to investigate the influence of pyramids size on the contact shading loss mechanism of silver (Ag) screen-printed p-type c-Si solar cells. Three alkaline texture solutions with sodium silicate additives were optimized to develop the small pyramid (0.5–2.0 µm) size, middle pyramid (5.0–9.0 µm) size and large pyramid (10–15 µm) size on the c-Si surface, respectively. It was noticed that screen-printed finger width strongly depends on pyramid size. Even though, same mesh patterns and screen printing conditions resulted in 20 µm widening of metal finger width on the large pyramids as compared to the small pyramids. This was attributed to the increase in the size of cell surface pyramids that not only varied the gap between the screen mesh and cell surface while screen-printing but also hindered the contraction of metal electrodes during the firing process. The c-Si solar cells with large pyramids suffered from an extra shading loss during fabrication, thus, led to the reduction of the short circuit current density (~0.7 mA/cm2) resulting in lower efficiency (~17.72%) as compared to efficiency (~18.60%) of small pyramid based cells.

Growth and optical properties of GaN pyramids using in-situ deposited SiNx layer

Self-assembled GaN pyramids were successfully fabricated on a SiNx layer that was grown in situ by metal-organic chemical vapor deposition. The diameter and height of a single pyramid was approximately 6–10 μm, and the structure had six (10–11) semi-polar facets. According to micro-photoluminescence measurements obtained at different excitation power densities, the polarization field on the sidewall of the pyramids containing InGaN/GaN multiple quantum wells was weak. The mechanism of atomic migration was deduced from the cathodoluminescence results. This type of structure can possibly be used for the fabrication of light-emitting diodes with multi-color emission.

Molecular and crystal structure and the Hirshfeld surface analysis of 1-amino-1-deoxy-α-d-sorbopyranose and 1-amino-1-deoxy-α-d-psicopyranose (“d-sorbosamine” and “d-psicosamine”) derivatives

Sorbosamine and psicosamine are the last two 1-amino-1-deoxy-hexuloses for which no structural data were available. We report on a13C NMR and a single crystal X-ray diffraction study of 1-deoxy-1-(N-methylphenylamino)-d-sorbose (1) and 1-deoxy-1-(N-methylphenylamino)-d-psicose (2). In solutions, both aminosugars are conformationally unstable and establish equilibria, with 90.7% α-pyranose, 3.8% α-furanose, 1.0% β-pyranose, 0.5% β-furanose, and 4.0% acyclic keto form for 1 and 32.4% α-furanose, 27.2% α-pyranose, 21.0% β-pyranose, 9.1% β-furanose, and 11.0% acyclic keto form for 2. X-ray diffraction data provided detailed structural information on 1 and 2 in the α-pyranose form. Both molecules adopt the 5C2 ring conformations, the bond distances and valence angles compare well with respective pyranose structures. All hydroxyl groups in crystal structures of both 1 and 2 participate in two-dimensional hydrogen bonding networks, the H-bonding pattern in 1 is dominated by co-crystallized water molecules. The Hirshfeld surface analysis revealed a significant contribution of non- or weakly polar interactions to the packing forces for both molecules, with crystal structure of 2 featuring short H⋯H contacts. Other structural features found in 2 are a significant planarity of the tertiary amino group (the pyramid heights are 0.127 Å in 2 vs 0.231 Å in 1), a concomitant non-involvement of the amine nitrogen in heteroatom contacts, and a unique anti-periplanar conformation around the C1C2 bond.

Study of the Enhancement of the Efficiency of the Monocrystalline Silicon Solar Cell by Optimizing Effective Parameters Using PC1D Simulation

In this paper, simulation of a monocrystalline silicon solar cell was done using PC1D software. The impact of different solar cell parameters, with their effects on power and efficiency, has been investigated. For a p-type monocrystalline silicon wafer, with an area of $10\times 10$ cm2 and a thickness of 300 μm, initial simulation shows a 12.10% efficient solar cell. To optimize the simulation experimentally obtained data has been used in the texturization process. It is seen that the textured surface reduces reflection and increases the efficiency of the solar cell at least 1–2%. From the simulation it is seen that the optimum value of p-type doping concentration is $1\times 10^{17}$ cm− 3 and n-type doping concentration is $1\times 10^{18}$ cm− 3. 200.3 μm diffusion length is considered as optimum. Both sides textured wafer with pyramid height of 2–3 $\mu \mathrm {m}$ and equal angles of 54.74 degrees produces the best result in simulation. An anti-reflection coating with 2.019 refractive index and a thickness of 74 nm is considered as optimum. By optimizing the effective parameters, a 20.35% efficient solar cell has been achieved by simulation.

Fabrication and Identification of the Efficiency of a Si-Based Solar Cell

This research represents the fabrication and characterization of a solar cell which is based on a thin p-type silicon (Si) wafer. Solar cells are the basic building blocks of Solar Panels or Modules. There are presently nine companies manufacturing solar modules in the country. Nowadays a large amount of electricity comes from solar cell. The total demand for solar cells in assembling solar modules of the nine companies are about 80-90MWp annually. Mainly, cost of solar cell depends on the Brand, type of crystal structure (Mono or Multi) and the shape or size of wafer. For the first time in the country, ‘Bangladesh Atomic Energy Commission (BAEC)’ has set up a laboratory to fabricate crystalline solar cells on a pilot basis. The method used to fabricate solar cells is the low-cost diffusion technique using POCl 3 gas source. Several solar cells of 150×150 mm 2 sizes and 200 micrometer thick are produced and characterized in the laboratory. A p-type silicon wafer is cleaned and textured to make its surface pyramid shape for absorbing more sunlight. The p-n junction used in Si-based solar cell is created after applying diffusion technique using Phosphorus-oxy-try chloride (POCl 3 ) within the silicon wafer and putting Aluminum (Al) paste on one side of the wafer. Perfectly texturing ensures the excellent pyramid height of the silicon wafers. The pyramid heights of raw, textured and doped wafers are 8233.2 A, 15222.5 A and 55654.1 A respectively. The pyramid surface shows the increasing light absorption by the solar cell that can lead to an increase in conversion efficiency of the device. The efficiency of the produced solar cell is 3.3%. The results have shown that some challenges and good opportunities in getting the high-efficient and cost effective solar cells. If the cost effective technology can be made familiar in Bangladesh then it will help in solving the power crisis in the country a great deal.

Crystal and Electronic Structure of High-Temperature Superconductive Layered Cuprates in Temperature Interval 100–300 K

For two HTSC materials, Y1−x Ca x Ba2Cu3 O 6.7 and Tl0.8Hg0.2Ba2Ca2Cu3 O 8.15, their crystal structure has been studied earlier in the temperature interval 100–300 K. It is shown that for both compounds, the height of CuO5 pyramids has a minimum in temperature interval from ∼ 150 to ∼ 250 K. The electronic structure is calculated using first principles based on the obtained data of crystal structure. It is revealed that a decrease in the CuO5 pyramid height leads to the appearance of the electronic state density peak with an energy of 0.3–0.4 eV under Fermi level. Localized states of barium and apical oxygen make the main contribution to this peak. By reduction the temperature below ∼ 150 K, these localized electronic states disappear, and under continuous cooling, the superconductivity appears.

Enabling stress determination on alkaline textured silicon using Raman spectroscopy

Confocal micro-Raman spectroscopy allows for spatially resolved measurements of the phonon energy in silicon, which is correlated to mechanical stress. Mechanical stress is a tensorial quantity. For the confocal measurement geometry and certain crystal orientations approximations have been derived in the past which correlate the shift of the Raman frequency to a scalar stress value. For optimization of mono-crystalline solar cell manufacturing steps the determination of induced mechanical stress from the top view perspective is desirable. However, this method is so far restricted to planar wafers or cross sections. we find that the anti-reflection surface texture strongly affects the measurement result. To enable quantitative stress determination of alkaline textured silicon a suited measurement procedure is investigated using 3-point bended solar cell segments. Preceding elasticity test revealed Young’s module and allowed a prediction of maximum stress values for any bending radius. We propose a measurement procedure which yields an observable shift of the Raman frequency proportional to the induced stress. We state the requirements for determination of a calibration factor to quantify stress on any alkaline textured solar cell. Adapting the conversion factors allows calibrated measurements for textures with different average pyramid heights. By varying the numerical aperture and the focus setting even changes of the induced stress within the texture pyramids are resolved.

Finite element analysis of ultrasonic vibration-assisted microstructure hot glass embossing process

Hot glass embossing is a novel technology to manufacture microtips for Field Emission Displays with high quality and low cost. This technology recently has been assisted by ultrasonic vibration. Previous studies showed that high energy of ultrasonic vibration would lead to the temperature rise inside the glass so that micro-formability of glass material has been especially improved efficiently. However, these findings were experimental only. Therefore, this work is aimed to utilise the proposed model in the previous study to analyse the shape of pyramid structures on K-PSK100 optical glass substrate during ultrasonic vibration-assisted hot glass embossing process. Microstructure hot embossing experiments were first conducted without and with the assistance of ultrasonic vibration (frequency of 35 kHz and amplitude of 3 μm). Three-dimensional simulations were then performed to predict the height of pyramids after hot embossing process. The consistency between simulations and experiments not only proved that ultrasonic vibration could increase the filling ability of glass material into microcavities up to 17% but also indicated the value of the proposed model in predicting the final shape of microstructures after ultrasonic vibration-assisted hot glass embossing process.

Higher values of spectral response, absorption coefficient and external quantum efficiency of solar cell in the form of pyramids

This paper presents a study on spectral response, absorption coefficient and external quantum efficiency of solar cell in the form of pyramid [1, 2]. We investigate to what extent and under what conditions we want to take advantage of ray incidence Seven times [3, 4]. It is found that these analyses can be used to determine the optimal surface texture which provides the best light trapping for solar cells in terms of the total internal reflection occurring in the high-index medium at incidence angles larger than the nominal critical angle [3–9]. One of the main contributions of this paper is the analysis and quantification of the influence of the opening between the heads of the two closest pyramids in textured surface for solar cells and its application on the photovoltaic parameters. In this model we show that the material can have seven successive incident ray absorptions instead of five currently, where we changed the direction of the reflected ray, by identifying and install the angle between the two neighbouring pyramids, the incidence angle, the opening between the heads of the two closest pyramids and their height. Thus, with an angle between the two neighbouring pyramid fixed at 12° and for angle of incidence fixed at 84°. For these values of the angle between the two neighbouring pyramids and incidence angle, the opening between the heads of the two closest pyramids fixed at 2.10 μm for a pyramid height of 10 μm. This leads to the largest possible increase in optical efficiency, such as spectral response, Absorption Coefficient and External Quantum Efficiency. The results are in good agreement with the available literature.

High-efficiency c-Si based interdigitated point contact back heterojunction solar cells

We report on the modeling and performance optimization studies of point contact back heterojunction (BHJ) solar cells. BHJ solar cell technology is a combination of front heterojunction (a-Si:H/c-Si) solar cell technology and interdigitated back junction c-Si solar cell technology. In this work, both emitter (p+-a-Si:H) and back surface field (BSF, n+-a-Si:H) were formed at the rear side as an array of interdigitated points, where their respective contacts formed an interdigitated pattern. The gap between p-type and n-type contact fingers was fixed at 10 µm. The n+-a-Si:H (i.e. BSF) circular diameter was fixed while emitter size was varied, and vice versa. Simulation was also performed with and without passivation layer underneath emitter and BSF. We also investigated the impact of surface texture size on cell efficiency. By varying surface texture size, viz. pyramid height and base width, an efficiency as high as 26.61% was obtained with 761 mV Voc, 41 mA/cm2 Jsc, and 84.5% FF for a small pyramid structure with 2 µm height and 4 µm base width.

Scanning tunneling microscopy of a graphene layer placed on a micro structured substrate

The features of the surface topography and the local energy spectrum of the graphene layer placed on a two-dimensional array of GaN pyramids are studied using scanning tunneling microscopy and local tunneling spectroscopy. This structure can be used as a test structure for the application of graphene as a flexible conductive transparent electrode in optoelectronics. Sagging of a graphene layer in the space between pyramids is found and the sagging value is estimated to be about 20% of the pyramid height of 1.1 μm. Local energy spectra show the change of the graphene electron energy spectrum due to the mechanical stress at sagging.

Improvement of quantum efficiency using surface texture of solar cell in the form of pyramid

The work presented in this paper is concerned a detailed study about the light transmission through textured surfaces in a surface made up of pyramids [1, 2]. We investigate to what extent and under what conditions we want to take advantage of ray incidence five times and more [3, 4]. It is found that these analyses can be used to determine the optimal surface texture which provides the best light trapping for solar cells in terms of the total internal reflection occurring in the high-index medium at incidence angles larger than the nominal critical angle [5–11]. One of the main contributions of this paper is the analysis and quantification of the influence of the opening between the heads of the two closest pyramids in textured surface for solar cells and its application on the photovoltaic parameters such as the quantum efficiency. In this model we show that the material can have five and more successive incident ray absorptions instead of three currently, where we changed the direction of the reflected ray, by varying the angle between the two neighbouring pyramids, the incidence angle, the opening between the heads of the two closest pyramids and their height. Thus, with an angle between the two neighbouring pyramid varying between 20° and 12° and for angle of incidence varying between 80° and 84°. For these values of the angle between the two neighbouring pyramids and incidence angle, the opening between the heads of the two closest pyramids varied respectively from 3.53 to 2.10 µm for a pyramid height of 10 µm. This lead to a substantial increase of the quantum efficiency thus the photovoltaic efficiency.

Effect of Supplemental Heat in Captive African Leopard Tortoises (Stigmochelys pardalis) and Spurred Tortoises (CENTROCHELYS sulcata) on Growth Rate and Carapacial Scute Pyramiding

Carapacial scute pyramiding (CSP) is common in captive-raised turtles and tortoises. Several dietary and environmental hypotheses have been proposed to explain this phenomenon, but few have been scientifically investigated. The effect of increased heat exposure on CSP and growth was examined in juvenile African leopard (Stigmochelys pardalis) and spurred (Centrochelys sulcata) tortoises. Monthly measurements of individual tortoise surface temperature, length, height, width, weight, and pyramid height of treatment (heat) and control (no heat) groups for 2 years were higher in the treatment groups. Allometric comparison further revealed increased pyramiding in the treatment group. Humidity and diet did not differ between treatment and control groups. The results of this research investigation indicate that growth rate and CSP appear to be directly related and both increase with excess nocturnal heat. The significance of the atypical carapace growth and subsequent consequences for naturally occurring tortoise populations, especially in the context of global climate change, is unknown but requires further investigation.

Nonlinear optical properties of GaAs pyramidal quantum dots: Effects of elliptically polarized radiation, impurity, and magnetic applied fields

The effects of the magnetic field and impurity position on the electronic states and nonlinear light absorption in a GaAs pyramidal quantum dot are investigated. The calculations were performed by using the total optical susceptibility for an incident light elliptically polarized along the pyramid growth axis. We proved that: (i) the optical susceptibility can be considerably modified by moving the impurity along the pyramid height; (ii) the enhancement of the magnetic field blueshifts the transition energies and increases the magnitude of the absorption coefficient; (iii) the light dispersion and absorption, as well as the group velocity can be controlled by changing the light intensity and its ellipticity parameter, without supplementary geometrical manipulations.

Optical reflectance of alkali-textured silicon wafers with pyramidal facets: 2D analytical model

Abstract

The effect of front pyramid heights on the efficiency of homogeneously textured inline-diffused screen-printed monocrystalline silicon wafer solar cells

The majority of industrial monocrystalline silicon (c-Si) wafer solar cells are alkaline textured (at least the illuminated surface) to reduce reflection and increase absorption of incident light. Therefore, understanding the influence of front pyramid heights on the solar cell parameters is essential for further improving cell efficiency. In this work we report the impact of pyramid height on the performance of inline-diffused c-Si solar cells. Three alkaline texture processes with potassium silicate additives are optimised to result in homogeneous coverage of pyramids. By modifying the process, surface textures with small (∼5 μm maximum), medium (∼6 μm maximum) and large (∼8 μm maximum) pyramid heights are formed. The impact of pyramid size on cell parameters is experimentally studied using industrial-grade 156-mm pseudo-square p-type Czochralski wafers. It is found that within the pyramid size range studied here, there is no significant variation in effective minority carrier lifetime, reflectance, open-circuit voltage or short-circuit current. However, fill factor and hence efficiency is significantly impacted by pyramid size. While cells in all three groups demonstrate high fill factor (>79%), it is shown that an average fill factor gain of up to 1% absolute can be achieved by using the best-suited texture process.

Modeling of GPU computing using difference schemes

We propose models of GPU (graphics processing unit) computing that can be recommended for implementation of explicit and implicit difference schemes on GPUs. In particular, these are models for selecting an optimal vector length in the 'long-vector' algorithms and for finding an optimal pyramid height in corresponding parallel algorithms.

Selective-emitter crystalline silicon solar cells using phosphorus paste

Selective-emitter structures have been studied to improve the conversion efficiency of crystalline silicon solar cells. However, such structures require additional complicated processes and incur extra cost. In this work, we used phosphorus paste (P-paste) to form a heavily-doped region beneath the grid and POCl3 to create a shallow emitter area. This method should be convenient to use in the solar-cell industry because it requires only additional P paste printing, compared to the case of homogeneous solar cells. Diffusion parameters including the temperature, diffusion time, and ambient gases were optimized. We observed that the spreading of the P paste was affected by the pyramidal size of the textured wafer due to the low viscosity of the P paste. The pyramidal height of the textured silicon surface was optimized at 3 μm to counterbalance the surface reflectance and the spreading of the P paste. The short-circuit current density of the completed selective emitter solar cell was increased, and an improvement of blue response in the internal quantum efficiency was seen while contact properties such as the fill factor deteriorated due to the spreading of the P paste and the thin emitter on top of the pyramid of the textured silicon surface. Double printing of the P paste was applied to solve this contact problem; a fill factor improvement of 2.4% was obtained.

Influence of random pyramid surface texture on silver screen-printed contact formation for monocrystalline silicon wafer solar cells

Most industrial monocrystalline silicon wafer (mono-Si) solar cells are metallised by screen printing. Silver (Ag) pastes are commonly used to form electrodes to phosphorus-doped n+ Si. However, there is still ambiguity about the influence of the random-pyramid surface texture on Ag screen-printed contacts for mono-Si solar cells. We present an experimental study to investigate this influence using screen-printed p-type mono-Si cell groups fabricated with a controlled variation in the alkaline surface texturisation process. It is observed that cell groups fabricated on Czochralski (Cz) wafers with smaller pyramids achieve higher average fill factor (FF) and lower average specific contact resistance than cell groups fabricated on Cz wafers with larger pyramids. To explain these observations, the pyramid texture height distributions are characterised statistically and the distribution statistics are correlated to electrical solar cell measurements and microstructure investigations of the Ag/n+ Si contact interface. Microstructure investigations reveal that most Ag crystallite growth is concentrated around the upper part of the pyramids and hence pyramid density is identified as an important parameter influencing contact formation. The influence of average pyramid height and pyramid height uniformity within a pyramid texture height distribution is also clarified with regards to contact formation. It is further observed that direct Ag crystallite contacts to the bulk Ag metallisation are not a prerequisite for achieving high FF (>80%). Based on the study, guidelines are developed for tailoring random-pyramid surface textures to optimise Ag screen-printed contact formation to n+ Si for mono-Si solar cells.