Investigation of morphological, optical and structural properties of multi-layer coatings for solar energy
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T.C. : SOLAR ENERGY MATERIALS AND APPLICATIONS
Investigation of morphological, optical and structural properties of multi‑layer coatings for solar energy Kadhim R. Gbashi1 Received: 27 September 2019 / Accepted: 18 February 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The multi-layers of nanomaterials, for the time being, are materials of great significance in the field of nanoscience. In this work, some of the physical, morphological and structural properties of multi-coatings for solar energy applications have been studied. We investigated the impact of surface roughness with the number of layers on the optical and structural properties. Decreasing surface roughness led to improve performance of transmittance, reduce reflectance, and increase bandgap for single-, double-, triple-, and quadruple coatings of semiconductors. Moreover, the decreasing in crystallite size and changing in lattice parameter are due to more strain effect on peak broadening of the crystal structure. The experimental observations are supported by simulation based on the surface roughness with the energy gaps and refractive indices, and film morphology was studied by scanning force microscopy and scanning electron microscopy, optical properties studied by UV–visible spectroscopy and structural properties investigated by X-ray diffraction. Keywords Multi-layer coatings · Surface morphology · Strain · Structural properties
1 Introduction Antireflection coating has been used in various applications such as solar cells and antiglare coatings for lenses and was first used to military optical instruments to decrease light quantity reflected from the lens surfaces [1]. These coatings were initially one layer of CaF2 and then MgF2. Magnesium di-fluoride ( MgF2) has high transparency (T) and low refractive index (n) and has been used as antireflection coating to reduce reflection losses [2]. Antireflective coating gives significant optimization in solar cell efficiency [3]. Antireflection coating techniques have been offered such as single layer [4], double-layer [5], multi-layer [6, 7], gradedindex layer [8] and stacked index layer structures [9, 10]. It has been declared that one-layer coating is minimizing reflectivity in a narrow spectral range, and reflectivity could be decreased by making double or even multi-layers [11]. These coatings have been designed by many thin layers of different compounds to optimize the transmission across the wavelength region absorbed within the solar cell. Due to * Kadhim R. Gbashi [email protected] 1
the high refractive index of the chemical compounds, high reflection losses should be minimized by antireflection thin films [5], for multi-junction [12, 13] solar cells. Among the various possible combinations of double-layer antireflection coatings, the combinations such as M gF2/ZnS, MgF2/TiO2, SiO2/SiNx and M gF2/CeO2 have already been reported. The most efficient antireflection coatings in practice are the magnesium fluoride/zinc sulfide ( MgF2/ZnS) double layers, w
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