Khalid Omar

The effect of porosity on the properties of silicon solar cell

Purpose – The purpose of this paper is to describe how fabricate solar cell based‐on porous silicon (PS) prepared by electrochemical etching process is fabricated and the effect of porosity layer on the solar cell performance is investigated.Design/methodology/approach – The techniques used include SiO2 thermal oxidation, ZnO/TiO2 sputtering deposition and PS prepared by electrochemical etching. Surface morphology and structural properties of porous Si were characterized by using scanning electron microscopy. Photoluminescence and Raman spectroscopy measurements were also performed at room temperature. Current‐voltage measurements of the fabricated solar cell were taken under 80 mW/cm2 illumination conditions. Optical reflectance was obtained by using optical reflectometer (Filmetrics‐F20).Findings – Pore diameter and microstructure are dependent on anodization condition such as HF: ethanol concentration, duration time, temperature, and current density. On other hand, a much more homogeneous and uniform d...

pH effect on cellular uptake of Sn(IV) chlorine e6 dichloride trisodium salt by cancer cells in vitro.

The effects of pH value and presence of serum in an incubation medium on photosensitizer drug cellular uptake in MCF7 cancer cells have been investigated. The results showed that the presence of serum in an incubation medium reduced the drug cellular uptake at all pH values. It has been found that decreasing on pH values of the incubation medium increased the cellular uptake of the drug, demonstrating selective uptake of the sensitizer. The HepG2 liver cancer cells exhibited more drug cellular uptake than CCD-18CO normal colon cells, which assessed the selectivity uptake of photosensitizer on cancerous cells. The concentration of photosensitizer measured in 106 cells showed a good correlation to the incubation time. Fluorescence and absorption spectroscopy been have used to examine the cells.

Mitigation of workplace radon gas concentration using high-performance epoxy resin coating

The indoor radon gas released from concrete was measured using a 0.65 × 0.65 × 0.65 m fabricated concrete slab room, simulating a workplace. The indoor radon gas concentration was monitored, and the remediation method was examined. Radon concentrations were monitored using Radon Monitor Model 1023 from Sun Nuclear. Results show that average radon concentrations reached 111 Bq.m–3 before remediation, beyond the World Health Organization’s acceptable limit of 100 Bq.m–3. Hence, two layers of high-performance waterborne epoxy resin TRU-GLAZE-WB 4030 coating were applied, reducing the radon concentration average to an acceptable level of 14.8 Bq.m–3. Interestingly, the indoor radon concentrations were measured two months after applying the remediation and were found to be stable and within acceptable levels.

Optical Insights into Enhancement of Solar Cell Performance Based on Porous Silicon Surfaces

The amount of light reflection from the surface is the main obstacle in efficient solar cell performance because reflection is related to the refractive index of the material. For instance, the silicon (Si) refractive index is 3.5, (which can rise by up to 35%), which prevents an electron-hole pair from being generated and could reduce the efficiency of photovoltaic converters. Antireflection coatings ARC are able to reduce surface reflection, increase conversion efficiency, extend the life of converters, and improve the electrophysical and characterization of photovoltaic converters [1]. Porous Si (PS) is attractive in solar cell applications because of its efficient ARC and other properties such as band gap broadening, wide absorption spectrum, and optical transmission range (700–1000 nm). Furthermore, PS can also be used for surface passivation and texturization [2–6]. The potential advantages of PS as an ARC for solar cells include surface passivation and removal of the dead-layer diffused region. Moreover, PS is able to convert higher energy solar radiation into spectrum light, which is absorbed more efficiently into bulk Si [7]. The vibrations, electronic, and optical properties of PS have been studied using various experimental techniques. Of these, the electrochemical etching process is a promising technique for fabricating PS [8–11]. According to the quantum confinement model, a heterojunction can be formed between the Si substrate and porous layers because the latter has a wider band gap (1.8–2.2 eV) compared with crystalline Si (c-Si) [12]. Recently, Ben Rabha and Bessais [13] used chemical vapor etching to perform the front PS layer and buried metallic contacts of multicrystalline silicon solar cells to reduce reflectivity to 8% in the 450–950 nm wavelength range, yielding a simple and low-cost technology with 12% conversion efficiency. Yae et al. [14] deposited fine platinum (Pt) particles on multicrystalline nSi wafers by electroless displacement reaction in a hexachloroplatinic acid solution containing HF. The reflectance of the wafers was reduced from 30% to 6% by the formation of porous layer. Brendel [15] performed electrochemical etching of PS layer into the substrate based on homoepitaxial growth of monocrystalline Si films, yielding a module efficiency of 10%. The present work aims to investigate the effect of PS on performance of Si solar cells. Optical properties such as refractive index and optical dielectric constant are investigated.

High photoluminescence of silicon nanostructures synthesized by laser‐induced etching

Purpose – The purpose of this paper is to synthesize Si (porous silicon (PS)) by laser‐induced etching (LIE) technique. The LIE process has the added advantage of a controlling size and optical properties without using of electrodes. The LIE process is a promising technique for fabricating many optoelectronic devices including: light‐emitting devices, detectors, sensors and large‐scale integrated circuits.Design/methodology/approach – PS has been fabricated by LIE technique. Surface morphology and structural properties of nanostructures are characterized by using scanning electron microscopy and X‐ray diffraction (XRD). Photoluminescence (PL) measurement is also performed at room temperature by using He‐Cd laser (λ=325 nm) and Raman scattering has been investigated using Ar+ laser (λ=514 nm).Findings – Surface morphology indicated that chemical reaction has been initiated with laser power density of 12 W/cm2, resulting in irregular structure. Micro‐columns are structured on surface with laser power densit...

The Methodology Effects on Surface Morphology Pattern of Porous Semiconductors

Porous GaP have studied fabricated by using an argon‐ion laser beam (LIE) of energy 2.41 eV. We have studied the surface morphology of porous layers obtained using a Scanning Electron Microscope (SEM). The morphology of porous GaP layers changes rapidly with laser power densities and irradiation times. This advanced fabrication method have been used for synthesis porous silicon (p‐Si). The optical characteristic was used to illustrate changes in surface morphology and the intensity of emission of porous form as a function of etching conditions. The surface morphology studies have demonstrated the characterization of porous silicon. As well as both the size and shape of the structure depend on the nature concentration of etchant solution. The different size of pores form at different area of GaN shows that the etching rate is not uniform through out the whole surface of GaN. The porous GaN generated by electrochemical etching technique does not always produce similar surface morphology. However, the averag...

Effect of etching time on porous silicon processing

The fabrication of porous silicon (PS) layers based on the crystalline silicon wafer n-type of (100) orientation using electrochemical etching process was conducted. The effect of various etching times on the structural and optical properties of the PS layers was investigated. The surface morphology of the PS layers was characterized using Scanning Electron Microscopy (SEM). Photoluminescence measurements of the PS layers were performed at room temperature. Additionally, the reflectance of the PS layers was obtained using an optical reflectometer. The results revealed that the PS layer at 10 min etching time exhibited excellent light trapping of a wide wavelength spectrum, which is expected to enhance the efficiency of optoelectronic devices.

Number of p-type distributed Bragg reflectors effects on gallium nitride (GaN)-based vertical cavity surface emitting laser performance

This paper has presented the characteristic features of the reflectivity of the output mirror at 415 nm vertical cavity surface emitting lasers with various distributed Bragg reflectors pairs. For this, vertical cavity surface emitting lasers with various corresponding p-distributed Bragg reflectors pairs are simulated using integrated system engineering simulation program. The output power and the threshold current for each of these devices were determined. We found that by increasing distributed Bragg reflectors pairs, the distributed Bragg reflectors reflectivity increased, which can reduce the device lasing threshold. However, the external differential quantum efficiency was inversely related to top mirror reflectivity. So, the optical output of the device also decreased with increased p-type mirror pairs. A suitable distributed Bragg reflectors design is carefully selected for the pair number so as to balance among low lasing threshold current, high output power, and high efficiency.

The Studies Of Doping Concentration Effects On VCSEL Laser

The numerical investigation of the performance of 850 nm GaAs single quantum wells (SQW) vertical cavity surface emitting laser (VCSEL) structure was carried out. Laser technology‐integrated program ISETCAD simulation has been used to investigate the effect of the doping concentration on the output power performance. We proposed a new model where a few low‐doped distributed Bragg reflector (DBR) layers are introduced just after spacer layers in order achieve a better matching of lattice constants. High output power and better efficiency were obtained with the proposed VCSEL structure. A very small deviation from the proposed structure will essentially affect the features of the light output. All material parameters are evaluated based on the recent literature values.

The Size Effect in Small Aperture Confined Vertical Cavity Surface Emitting Laser

A numerical study has been preformed for the oxide‐confined vertical cavity surface emitting lasers (VCSEL) operating at 850 nm region of the electromagnetic spectrum. Relevant VCSEL design with numerous oxide aperture sizes has been designed and characterized by using laser technology‐integrated program ISETCAD simulation. In this paper, the effect of oxide aperture size is studied by changing the size of aperture from 1 to 8 μm. The investigations of electrical as well as optical characteristics of the designed VCSEL have been performed, which include the overall device performance as a function of oxide aperture size. It is observed that the increase in the aperture radius of the VCSEL cause increase in both the threshold current to up 4.578 mA and output power up to 37.85 mW. Furthermore, the slope output efficiency of up to 1.003% corresponding to differential quantum efficiency up to 68.65% was obtained.