Papers by Keyword: Absorption

Abstract: In this work, ray tracing is used to investigate the effects of pyramid texture angle towards light absorption and photocurrent in 250 μm-thick crystalline silicon (c-Si) absorber. Upright pyramids with texture angles of 10-50^o are investigated. Planar c-Si absorber is used as a reference. When the pyramid angle increases, the broadband reflection reduces due to enhanced light scattering which leads to improved light absorption. At angle of 50^o, the weighted average reflection (WAR) reduces to 14.7% and broadband light absorption increases. The optical path length enhancement increases to 12 at wavelength of 1100 nm. The reflection and photogenerated current density (J_g) exhibit an inverse relationship with increasing zenith angle. With increasing zenith angle, the reflection from the c-Si absorber increases and this results in lower light absorption and J_g. In the passivated emitter rear cell (PERC) solar cell, the planar solar cell exhibits short-circuit current density (J_sc) of 26 mA/cm² with conversion efficiency of 13.6%. When both the pyramids and the silicon nitride (SiN_x) anti-reflective coating (ARC) are incorporated on the solar cell, the J_sc increases to 39 mA/cm² and conversion efficiency increases to 20.5%. This is attributed to the enhanced light-trapping and light-coupling effects in the device.

Abstract: In this work, the impacts of wafer doping type on structural and optical properties of black silicon (b-Si) fabricated by metal-assisted chemical etching (MACE) process are investigated. P-type and n-type mono-crystalline silicon (mono c-Si) wafers are etched in an aqueous solution of hydrofluoric acid (HF), silver nitrate (AgNO₃) and deionised water (DI H₂O) at room temperature and various durations from 5-20 minutes. Surface morphological results demonstrate the formation of b-Si nanowires (NWs) with average lengths of 0.4-0.8 μm for p-type wafers and 0.8-3.0 μm for n-type wafers. The higher length of the NWs for the n-type wafers is due to the minority charge carriers, which lead to a higher etching rate during the MACE process. Within the 300-1100 nm wavelength region, weighted average reflection (WAR) for the p-type and n-type wafers decreases to 6.6% and 6.4%, respectively, after 20 minutes of etching. The corresponding improvement in broadband light absorption results in maximum potential short-circuit current density (J_{sc (max)}) of 38.2 and 38.8 mA/cm² for the p-type and n-type b-Si, respectively, which is an of enhancement of 39.9% and 42.1% when compared to the J_{sc (max)} of planar c-Si reference.

Abstract: The aim of this study is to determine whether the effective medium approach (EMA) is suitable to model black silicon structures. The present study focuses on comparing EMA paired with 1D FDTD simulations to full 3D FDTD simulations. Comparison was done for ordered cylindrical and hemispherical b-Si nanostructures. From the simulation results, the 1D simulation seems to underestimate the transmittance and overestimate the reflectance for these structures. This was attributed to the failure of the EMA to capture scattering and diffraction effects that were present in the nanostructures. The absorptance spectrum was comparable for both 1D and 3D simulations, hence it was concluded that the simplification may be suitable for simplifying problems where calculating the absorption of light is desired.

Abstract: This work investigates properties of Poly (3,4-ethylenedioxythiophene)–poly (styrene sulfonate) (PEDOT:PSS) on black silicon (nanotextured) and hybrid textured (nanotextured/microtextured) surfaces. The black silicon (b-Si) surface is fabricated using two-step metal-assisted chemical etching (MACE) process on crystalline silicon (c-Si) while the hybrid textures are fabricated using two-step MACE process on microscale pyramids. With PEDOT:PSS, weighted average reflection (WAR) reduces from 9.2% to 7.7% for b-Si and from 7.2% to 5.2% for hybrid textures. This is due to the anti-reflective (AR) property of the polymer. Electrical characterizations of the PEDOT:PSS layer reveal higher sheet resistance (R_s), lower hole concentration (n_h) and improved mobility (μ_h) with the presence of the surface textures on c-Si, in comparison to the results from planar c-Si reference.

Abstract: The most widely used materials in building construction are porous materials and the combined effect of rising dampness with soluble salts is one major problem. This phenomenon is caused by the migration of the salt ions dissolved in water into the porous network of the construction materials in the building walls, which causes fractures in the materials after several cycles of crystallization/dissolution. This work presents an extensive experimental campaign with different cycles of water absorption (capillarity absorption tests) and drying (drying tests). The samples of building material used are red brick, and the samples were, previously, submitted to capillarity absorption tests with two different saturated solutions (sodium sulphate and potassium chloride). The results showed that the two salts studied influence the porous materials and their capillary coefficient in clearly different ways and the samples immersed in sodium chloride present higher drying rates than those immersed in a saturated sodium sulphate solution.

Abstract: The low resistance to compression and flexural of conventional earth techniques such as adobe in the occurrence of earthquakes causes the immediate collapse or failure of structures built with this material. These deficiencies are caused by the lack of stabilization and reinforcement processes of the block, which causes low mechanical performance in the face of seismic forces. The most common structures to collapse during earthquakes in developing countries such as Peru are the self-built adobe rural houses, being the most used in these areas due to the high housing deficit and the high demand for low-cost housing. One solution to this problem is the use of reinforced CEB in rural housing. In the present investigation some properties such as absorption, compressive strength and flexural strength are studied, the results indicate that the compressive strength and flexural strength increase when compared with an unstabilized earth block, however, the increase in absorption is proportional to the amount of fiber so it was used in small proportions less than 1% in the mixture

Abstract: This study aims to determine the absorption and ability of hydrogels to hold water. The hydrogel was synthesized using the freeze-thaw method, then the absorption ability and water retention time in the hydrogel were tested and characterized by FTIR and trinocular stereo microscope. The FTIR results showed that the resulting hydrogel had N–H, O–H, aliphatic C–H, bend N–H, C–O, and C–N functional groups. The highest absorption of the hydrogel with a ratio of cellulose:chitosan:EDTA variations of 2:2.25:0.25 (g) respectively, which was 287.46% and the appearance of the hydrogel under a microscope showed that the structure of the hydrogel was rather hollow, so that it affected its absorption.

Abstract: In the CH₃Cl/H₂ atmosphere, the adsorption process of various active chlorocarbon groups (CH₂Cl, CHCl, CCl) and CH₃ on the surface of clean diamond used density functional theory (DFT) calculations during CVD process. The reaction heat and activation energy of the active sites on the adsorption reconstituted surface of D-CH₃ and D-CH₂Cl were calculated by transition state search to explore the actual effect of the carbon chloride active group on the surface of CVD diamond (100).The results showed that the adsorption capacity of CHCl, CH₂Cl and CCl on the substrate was gradually weakened and the adsorption energy of CH₂Cl and CH₃ was close. Both CHCl and CH₂Cl could form diamond bonds with the substrate carbon atoms to directly promote the growth of the diamond coating. Since the C-Cl bond was weaker than the C-H bond, the adsorption recombination surface of CH₂Cl generated an energy barrier of the active site lower than the adsorption reconstitution surface of CH3. Therefore, using CH₃Cl/H₂ as a gas source could effectively reduce the energy required for diamond coating growth.

Abstract: This study investigated characteristics of moisture desorption for polylactic acid (PLA) filaments. The filaments tend to absorb moisture from humid air, led to moisten filaments. The absorption of even small amounts of moisture by filaments during storage and/or 3D printing, degraded the quality of final parts, and therefore, caused manufacturing problems. In this work, the filaments were subjected to humid conditions to achieve various moisture concentrations (0.75, 1.3 and 1.87 wt.%). Warm air-drying processes are used to reduce the moisture for different times (1, 2, 3, 4, 5 and 6 hours) and temperature (40, 50 and 60 °C). It was founded that the moisture from the polylactic acid (PLA) filaments can be discovered the moisture by use 60 degree of temperature in 5 hours warm air-drying process.

Abstract: . This investigation aims to improving mechanical properties of normal concrete such as compressive strength, tensile strength, and flexural strength by using integral waterproof admixture (IWP) and also decreasing absorption of concrete, using different mix proportions of concrete, study shows a good increment of compressive strength for all mixes by using integral waterproof and also increasing the flexural and tensile strengths. The study contains also a sulfate attack study on normal mixes and integral waterproof mixes. Different percentages of IWP used in the study containing 0.0%, 1% ,1.5% and 2% for each 100 kg cement. Concrete mixes with 2% IWP admixture and 1:1:1.5 mix proportions give the highest values of compressive, tensile, and flexural strength in the study. compressive strength improved from 33.6MPa for reference 1:1:1.5 mix to 39.8 MPa by using IWP, also less absorption concrete obtained, the absorption was lowered from 3.5% to 1.7%, also deterioration in strength due to sulfate attack was small compared with reference mixes, same to other mixes 1:2:4, 1:1.5:3 that also improved by IWP admixture and lead to increasing mechanical properties and reducing absorption and sulfate attack.