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. 2021 Feb 22;6(8):5276-5286.
doi: 10.1021/acsomega.0c05405. eCollection 2021 Mar 2.

Hydrophilic Antireflection and Antidust Silica Coatings

Mohammad Istiaque Hossain  1 , Brahim Aïssa  1 , Ayman Samara  1 , Said A Mansour  1 , Cédric A Broussillou  1 , Veronica Bermudez Benito  1
Affiliations

Hydrophilic Antireflection and Antidust Silica Coatings

Mohammad Istiaque Hossain et al. ACS Omega. .

Abstract

We report on the optical and morphological properties of silica thin layers deposited by reactive RF magnetron sputtering of a SiO2 target under different oxygen to total flow ratios [r(O2) = O2/Ar, ranging from 0 to 25%]. The refractive index (n), extinction coefficient, total transmission, and total reflectance were systematically investigated, while field-emission scanning electron microscopy, atomic force microscopy, and three-dimensional (3D) average roughness data construction measurements were carried out to probe the surface morphology. Contact angle measurements were performed to assess the hydrophilicity of our coatings as a function of the oxygen content. We performed a thorough numerical analysis using 1D-solar cell capacitance simulator (SCAPS-1D) based on the measured experimental optical properties to simulate the photovoltaic (PV) device performance, where a clear improvement in the photoconversion efficiency from 25 to 26.5% was clearly observed with respect to r(O2). Finally, a computational analysis using OptiLayer confirmed a minimum total reflectance of less than 0.4% by coupling a silica layer with n = 1.415 with another high-refractive-index (i.e., >2) oxide layer. These promising results pave the way for optimization of silica thin films as efficient antireflection and self-cleaning coatings to display better PV performance in a variety of locations including a desert environment.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
(a) GIXRD patterns of the thin films grown at [r(O2) = 25%] and 200 °C process temperature. (b) XPS survey, along with Si 2p and O 1s spectra of films grown at r(O2) = 25% shown in the insets. The inset on the left shows oxygen profiling from the XPS study of silica thin films grown at oxygen concentration r(O2) = 0–25%.
Figure 2
Figure 2
UV–vis–NIR measurement of the (a) transmittance and absorptance spectra and (b) reflectance spectra of the sputtered silica deposited on glass for various r(O2) oxygen contents.
Figure 3
Figure 3
Ellipsometry measurement of (a) refractive index (RI) and (b) extinction coefficient spectra of the sputtered silica on glass for various r(O2) oxygen contents.
Figure 4
Figure 4
Histogram representation of (a) refractive index measured at 633 nm of the sputtered silica on glass for r(O2) in the 0–25% range and (b) calculated silica band gaps for different oxygen partial pressures.
Figure 5
Figure 5
Contact angle measurements to assess the hydrophilicity of sputtered silica on glass substrates for various r(O2) values: (a) uncoated glass substrate and hydrophilic (CA ∼ 50°), (b) 0% and hydrophilic (CA ∼ 17.5°), (c) 5% and hydrophilic (CA∼ 6.4°), (d) 10% and hydrophilic (CA ∼5.8°), (e) 15% and superhydrophobic (CA ∼ 4.2°), (f) 20% and superhydrophilic (CA ∼ 3.8°), and (g) 25% and superhydrophilic (CA ∼ 1.5°).
Figure 6
Figure 6
Summary of the measured contact angle measurements of sputtered silica for various r(O2) values along with the reference sample, and its relationship to the refractive index. The dashed lines are a guide for the eye.
Figure 7
Figure 7
Typical SEM micrographs showing the surface morphology of the extreme oxygen content values: (a) r(O2) = 0% and (b) r(O2) = 25%.
Figure 8
Figure 8
Oxygen plasma treatment of the reference glass substrate. Contact angle measurement of the substrate: (a) preplasma treatment and (b) postplasma treatment.
Figure 9
Figure 9
AFM analysis of the (a) untreated glass substrate and (b) 5 min plasma-treated glass substrate.
Figure 10
Figure 10
SEM analysis of the (a) untreated glass substrate and (b) 5 min plasma-treated glass substrate.
Figure 11
Figure 11
Three-dimensional (3D) mode roughness measurement of the sputtered silica on glass for various r(O2) values: (a) reference glass substrate (Ra ∼ 6.35 nm), (b) 0% (Ra ∼ 14 nm), (c) 5% (Ra ∼ 17 nm), (d) 10% (Ra ∼ 22 nm), (e) 15% (Ra ∼ 26 nm), (f) 20% (Ra ∼ 27 nm), and (g) 25% (Ra ∼ 43 nm).
Figure 12
Figure 12
Device performance simulation using the optical properties of SiO2 layers. (a) Open-circuit voltage (Voc), (b) short-circuit current Jsc (mA/cm2), (c) fill factor (FF, %), and (d) power conversion efficiency (PCE, %). The silica thickness was varied from 0 nm (i.e., uncoated glass substrate) to 200 nm. The schematic of the simulated solar cell structure is shown at the top of the figure.
See this image and copyright information in PMC

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