Growth and characterization of silicon nanowires for solar cell applications

Silicon nanowires (SiNWs) have received considerable attention as base materials for third-generation photovoltaic (PV) devices because they lend themselves to large- scale production with enhanced light trapping and increased overall performance. Previous studies have grown SiNWs on indium tin oxide-coated glass substrates by the pulsed plasma-enhanced chemical vapour deposition method (PPECVD) using tin (Sn), aluminum (Al), gold (Au) and zinc (Zn) as catalysts. Various catalysts (Sn, Zn, Au and Al) with thin film thicknesses from 10nm to 100nm, were used in this study of SiNW growth. Surface morphology analysis, by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), of the grown SiNWs showed the influence of the catalyst type and thickness. The wires became thicker and shorter as the catalyst thickness increased. However, the SiNWs catalyzed by Al metal were thicker than those grown using Sn, Au and Zn metals. The density of the SiNWs decreased as the catalyst thickness increased. For example, the 10nm thick Al catalyst produced the greatest SiNW density of 20NW/μm2, whereas the 100nm-thick Au resulted in the lowest density of 6NW/μm2. The effect of catalyst type and thickness on the structural properties of the grown SiNWs was investigated through X-ray diffraction (XRD). The XRD measurements showed that the SiNWs grown with Au catalysts had higher crystallinity than those grown using other catalysts. Moreover, the diffraction peaks became sharper with increasing wire diameter, indicating that the crystallinity of the grown SiNWs was enhanced. The optical properties of the prepared SiNWs were investigated by photoluminescence (PL) and Raman spectra. A red emission band was clearly observed in the PL spectra of all the prepared SiNWs. In the Raman spectrum, the first-order transverse optical mode (1TO) was exhibited in all SiNWs catalyzed using Sn, Au, Al and Zn. However, the 1TO peak location depended on the catalyst type and thickness. Important results were observed at a catalyst thickness of 80nm for all catalysts because the 1TO Raman peak was closest to the crystalline Si peak location for all the prepared samples, except for the SiNWs prepared using 100nm of Au metal. The crystal size of the grown SiNWs was calculated from the Raman spectra. In general, the crystal size of the grown SiNWs using 10, 20, 40, 60 and 100nm of Sn, Al and Zn metals decreased with increasing thickness of catalyst. However, the SiNWs prepared using 80nm thick Sn, Al and Zn catalysts had the largest crystal size. In contrast, the crystal size of SiNWs catalyzed by Au increased with increasing the catalyst thickness. Several designs of solar cells based on SiNWs were fabricated by the PPECVD method at 400°C on an ITO-coated glass substrate using the two most promising catalysts, Zn and Au. The first one was a p-type SiNWs/i-amorphous Si/n-type amorphous Si (p-i-n) structure using the Zn catalyst. The photocurrent density of the fabricated device was 13.3mA/cm2 and the open-circuit voltage was 0.5V. A high- performance nanowire solar cell fabricated in this work had 2.05% light conversion efficiency. The other device structures were fabricated by doping SiNWs catalyzed with Zn and Au as p and n type to fabricate p-n homo-junction SiNW solar cells. The fabricated pn junction solar cell based on the Zn-catalyzed SiNWs showed a higher efficiency of 1.01% compared with the Au catalyzed SiNW solar cell with an efficiency of 0.67%. These promising results provide a basis for further studies aimed at optimizing the device designs

Fabrication and characterization of solar cells based on silicon nanowire homojunctions

Silicon nanowire homojunction p-n solar cells were fabricated using Zn and Au metals as catalysts for growing the NWs. This design consisted of SiNWs, doped as p and n-types, catalyzed with Zn and Au catalysts to fabricate p-n homojunctions within each wire. The surface morphology, structure, and photovoltaic properties were investigated. The morphology for each of the catalyzed SiNWs was significantly different; the Zn catalyst produced short and thick NWs with diameters ranging from 190nm to 260nm, whereas the Au catalyst produced long SiNWs with diameters ranging from 140nm to 210nm. The Zn-catalyzed SiNW p-n solar cell showed a higher efficiency of 1.01 % compared with the Au-catalyzed SiNW p-n solar cell with an efficiency of 0.67 %

Effect of Diffusion Temperature on the some Electrical Properties of CdS:In Thin Films Prepared by Vacuum Evaporation

CdS films were prepared by thermal evaporation technique at thickness 1 µm on glass substrates and these films were doped with indium (3%) by thermal diffusion method. The electrical properties of these have been investigated in the range of diffusion temperature (473-623 K)> Activation energy is increased with diffusion temperature unless at 623 K activation energy had been decreased. Hall effect results have shown that all the films n-type except at 573 and 623 K and with increase diffusion temperature both of concentration and mobility carriers were increase

Controlling the diameter of silicon nanowires grown using a tin catalyst

Silicon nanowires were grown on ITO-coated glass substrates via a pulsed plasma enhanced chemical vapor deposition method, using tin as a catalyst. The thin films of catalyst, with different thicknesses in the range 10-100 nm, were deposited on the substrates by a thermal evaporation method. The effect of the thickness of the thin film catalyst on the morphology of the silicon nanowires was investigated. The scanning/transmission electron microscopy images showed that the wire diameter increased as the thickness of the thin film catalyst increased. The nanowires grown using a thin film thickness of 10 nm were inhomogeneous in diameter, whereas the other thicknesses led to an increase in the homogeneity of the diameters of the nanowires. The dominant wire diameter of the grown silicon nanowires ranged from 70 to 80 nm with 10 nm catalyst thin film thickness, and increased to a range of 190-200 nm with 100 nm catalyst thin film thickness

Structural and optical properties of Au-catalyzed SiNWs grown using pulsed plasma-enhanced chemical vapour deposition

Silicon nanowires (SiNWs) were grown on indium tin oxide-coated glass substrates using pulsed plasma-enhanced chemical vapour deposition (PPECVD) with gold (Au) as a catalyst. Various thicknesses of Au thin films ranging from 10 nm to 100 nm were deposited on the substrates by thermal evaporation. The surface morphological study of the prepared wires showed that the wire diameter increased as the catalyst film thickness increased. The X-ray diffraction patterns of the prepared SiNWs illustrated that the grown wires had cubic phase, and the crystallinity was enhanced as the catalyst thickness increased. The photoluminescence spectra of the SiNWs had a red emission band whose band location and shape were found to be dependent on catalyst thickness. The Raman spectra of the prepared nanowires showed that the first order transverse band shifted toward lower frequencies compared with the c-Si band location. The first order transverse band approached the c-Si band location as the wire diameter increased due to the increasing catalyst film thickness

Preparation and characterization of silicon nanowires catalyzed by aluminum

Silicon nanowires (SiNWs) were grown on indium tin oxide coated glass substrates by a pulsed plasma-enhanced chemical vapor deposition (PPECVD) method using aluminum as a catalyst. The thin films of the catalyst, with thicknesses ranging from 10 nm to 100 nm, were deposited on the substrates by thermal evaporation. The effect of the thickness of the thin film catalyst on the morphology of the silicon nanowires was investigated. The surface morphology study of the prepared wires showed that the modal wire diameter increased as the catalyst film thickness increased. The X-ray diffraction patterns of the prepared silicon nanowires had no silicon peaks, indicating that the wires had low crystallinity. The photoluminescence spectra of the SiNWs showed that all samples had more than one emission band. The emission band location and shape were found to be dependent on catalyst thickness. The Raman spectra of the prepared nanowires showed that the first order transverse band shifted toward lower frequencies compared with the c-Si band location

Effect of radio frequency magnetron sputtering power on structural and optical properties of Ti6Al4V thin films

Abstract In this research, the effects of target sputtering power on the structure and optical properties of radio frequency (RF) sputtered Ti6Al4V films were investigated. Different sputtering RF powers were used to produce different thicknesses of Ti6Al4V thin films. From the X-ray diffraction, it was found that the Ti6A14V films had polycrystalline cubic and hexagonal structures and increased films crystallinity and crystalline size with increasing the sputtering power. Atomic forces microscopy (AFM) gave us a nanometric film character, films homogeneity, and surfaces roughness. A higher degree of roughness and average grain size with increasing RF power was exhibited. Band gap and refractive index of Ti6Al4V thin films varied with sputtering RF powers

Wear Resistance Improvement of Alloy Steel Using Laser Surface Treatment

Laser surface heat treatment has been accepted as an effective technique of surface hardening of steels because of the converging of the laser beam by the lens on a tiny spot with a diameter near the value of the laser wavelength, laser surface heat treatment has been an effective way to improve the surface properties of. There are many applications in the industrial of the laser technique. This concentrated a lot of energy into a tiny area, resulting in a lot of heat compared to traditional heating methods. Wear resistance is a surface phenomenon, although it is influenced by elements such as surface hardening, surface condition, and microstructure. In this research, the aNd-YAG laser was used to treat the surface of alloy steel in order to investigate the effects of irradiation on the microstructure, metal surface hardening, and wear resistance. Low surface roughness and increased surface microhardness have been achieved due to the laser pulse indicated (900 Hv). The wear resistance was discovered to be higher due to laser treatment with the selected conditions

Growth and characterization of silicon nanowires catalyzed by Zn metal via Pulsed Plasma-Enhanced Chemical Vapor Deposition

High-density silicon nanowires (SiNWs) were grown via Pulsed Plasma-Enhanced Chemical Vapor Deposition at 400 C. Zinc (Zn) metal thin films with varying thickness from 10 nm to 100 nm were used as a catalyst to synthesize the SiNWs. The surface morphology, crystalline structure, and optical properties of the grown SiNWs were investigated. Results indicated that increasing the Zn thickness from 10 nm to 100 nm led to an increase in wire diameter from 65 nm to 205 nm, resulting in a reduction of SiNW density. The wires grown with Zn thicknesses of 10 and 80 nm exhibited high crystallinity as shown by the X-ray diffraction patterns. Three emission bands (green, blue, and red) were observed in the photoluminescence spectra of the SiNWs prepared using various Zn catalyst thicknesses. The SiNWs prepared using 10 and 80 nm Zn thicknesses displayed a sharp Raman peak that corresponded to the first-order transverse optical phonon mode in contrast to the other samples that produced SiNWs with a broad Raman band