Mrs. Hajar Ghanbari, Dr. Rasoul Sarraf-Mamoory, Prof. Jamshid Sabbagh Zadeh, Mr. Ali Chehrghani, Dr. Rasoul Malekfar,
Volume 7, Issue 2 (8-2013)
Abstract
In this study, Highly Oriented Pyrolytic Graphite was ablated in various polar and nonpolar solvents by Q-switched neodymium: yttrium-aluminum-garnet laser (wavelength=1064 nm, frequency=2 kHz, pulse duration=240 ns). Then, the products were examined using Scanning Electron Microscopy and UV-Vis spectroscopy. The images showed that different carbon structures such as cauliflower-like structures in benzene, spiral integrated forms in toluene, organic integrated networks in hexane, and nanoparticles in ethanol were formed. In n-methyl-2-pyrrolidone (NMP), sheets and bulk deformed structures were seen. Also, in Dimethylacetamide, particles in different stages of growth could be detected. The nonlinear optical absorption (NLA) behaviors of the products were investigated by exposing them to a 532 nm nanosecond laser using the Z-scan technique. The saturated NLA coefficient, obtained from structures of NMP and hexane-based synthesized samples, are 1.1×10-8 and 2.4×10-8 cm W-1, respectively. The saturable absorption responses of these samples were switched to the reverse saturable absorption responses in the other synthesis mediums. The maximum nonlinear absorption coefficient of 10.2×10-8 cm W 1 was measured for spiral integrated superstructures, produced in the toluene medium.
Mandana Jalali, Hamid Nadgaran, Daniel Erni,
Volume 11, Issue 2 (8-2017)
Abstract
In this paper a novel anti-reflection (AR) coating based on silicon nano-bars is designed and its impact on the performance of crystalline silicon (c-Si) thin-film solar cells is extensively studied. Silicon nano-bars with optimized size and period are embedded on top of the active layer, under a 100nm Si3N4 layer. As a result of the proposed layer stack, an inhomogeneous intermediate layer with effective refractive index amid the two layers is formed and a graded refractive index AR coating is achieved, which has a substantial effect on broad, omnidirectional reduction of the reflection spectra. To validate our claim, the proposed structure as well as four conventional AR coatings are simulated and through the numerical analysis of both the spectral response of the reflection factor and the silicon active layer absorption spectra, it is shown that the proposed design outperforms conventional already existing AR coatings, and in addition provides a strong coupling of the incident light to the active layer, while improving the overall efficiency of the thin-film solar cell.
