Estimation of the porosity and refractive index of sol–gel silica films using high resolution electron microscopy

The relationship between the refractive index and the porosity of silica based anti-reflective coatings (ARCs) has been studied. The coatings were prepared with the traditional Stöber method. The refractive index was evaluated by fitting vis–NIR transmittance spectra to Fresnel׳s coefficient of refl...

Full description

Saved in:
Bibliographic Details
Published in:Solar energy materials and solar cells 2014-11, Vol.130, p.246-256
Main Authors: Tamar, Yair, Tzabari, Masada, Haspel, Carynelisa, Sasson, Yoel
Format: Article
Language:English
Subjects:
Anti-reflective
Applied sciences
Coatings
Cracks
Elongation
Energy
Exact sciences and technology
Mixing rule
Mixing rules
Natural energy
Porosity
Refractive index
Refractivity
Scanning electron microscopy
Silica
Solar energy
Sol–gel
Stober
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:The relationship between the refractive index and the porosity of silica based anti-reflective coatings (ARCs) has been studied. The coatings were prepared with the traditional Stöber method. The refractive index was evaluated by fitting vis–NIR transmittance spectra to Fresnel׳s coefficient of reflection using the transfer matrix method. The porosity was assessed by a novel method based on image processing of high resolution scanning electron microscope (SEM) images. Results were compared to the commonly used Yoldas and Maxwell–Garnett mixing rules. Our results showed better agreement with the Yoldas mixing rule than with the Maxwell–Garnett mixing rule, which was explained as being due to the presence of elongated crack shaped pores in the ARCs rather than randomly dispersed spherical shaped pores, as was evident in the SEM images. Furthermore, we found that despite the presence of the elongated cracks, the coating appears to behave towards light like a homogenous medium. This somewhat surprising result calls for further research. Lastly, we have shown that it is reasonable to assume that the ARC is vertically homogeneous in terms of its porosity and effective refractive index. •Silica anti-reflective coatings were explored.•The refractive index-porosity relationship was examined.•Porosity was assessed by a novel SEM image processing method.•Results showed proximity to Yoldas over Maxwell–Garnett model.•This result coincided with the elongated geometry of the pores.
ISSN:0927-0248
1879-3398
DOI:10.1016/j.solmat.2014.07.020