CHAPTER-1

INTRODUCTION

AND

REVIEW OF LITERATURE

Introduction

Anti reflection coating are used in a large variety of applications wherever light passes

throughout an optical surface, and very low reflectivity is preferred. An antireflective or anti-

reflection (AR) coating applies to the glass surface and other visual or optical device to reduce

reflection. This increases the effectiveness of the system, as less light is loss [1,2].

To reduce reflection from surface of lenses and other optical devices, an AR layer is a type

of optical coating applied for that, this improves the effectiveness of the system since a lesser

amount of light is lost.

The incoming radiation passes throughout the incident glass of solar cells before reaching the

active layer of the solar cell. Radiation i.e. reflected by the incident glass does not makes it way

in to active layers of the solar cells, thereby resulting in a less efficient solar cell. In other terms,

it would be desirable to decrease the amt of radiation that is reflected by the incident substrate,

thereby increasing of amt of radiation that makes its way to the active layer of solar cell. In

particular, the power out put of a solar cell module may be dependent upon the amt of light or

numbers of photons with in a specific range of the solar spectrum that pass throughout the

incident glass and reach the PV semiconductor.

One of the main loss mechanisms that any kind of Photovoltaic module is subjected to is the

loss from the glass aperture on the entrant side. This is applicable for both conventional Si

based module as well as thin film based cell/module; in addition solar heating modules are also

subjected to these losses. As much as 8% incident lights can be lost due to frontal reflection.

Thus, one of the aims of Photovoltaic industry has been to find out an effective and economical

way to improve the transmission profile of glass used in existing production process.

Broadly speaking, there are two kinds of techniques that are available for increasing in

transmission of glass; 1) interference technique, achieved by deposition of anti reflection coating

on glass surface and 2) developing a graded refractive index profile [3] at the surface of glass.

In the first method one needs multiple layers for making a broadband transmission window; also

the increase in transmission is inversely proportional to incidence angle and decreases

drastically at lower angle of incidence. The method is also expensive to produce and lastly and

very important from Solar application point of view, this method suffers from environmental

degradation severely. The second method, property of which was first enunciated by Lord

Rayleigh (in 1886) involves chemical action on the surface of a glass, which causes selective

etching/leasing of ions in the glass to cause a porous structure on the surface. Due to chemical

reactions with the environment, the optical glasses accessible at the time tend to develop

tarnish on its exterior with a time period. The structure thus formed is non-uniform so that the

refractive index formed is not linear but takes on a graded form and this causes a reduction in

reflectance from the surface. This technique also has the potential to be cost effective from the

point of view commercial manufacturing of solar panels.

The detail of this process was first described by Kinoshita (1964) and has been subsequently

improved upon by various and researchers such as Disteldorf and Nakajima [4]. However, the

above method and process described by all these authors are general in nature and does not

address the key issue of developing a stable process for application in the solar industry.

An extra category of AR coatings is called "absorbing anti reflecting coating", these are very

functional when higher transmittance throughout a face is unwanted but lower reflection is

necessary. With few layers, they generate very lower reflectivity and could frequently be formed

very inexpensively rather than standard non-absorbing anti reflecting coatings. Absorbing anti

reflecting coatings frequently making utilize of extraordinary optical characteristics show in

complex thin films formed by sputtering process like “titanium nitride & niobium nitride” used for

anti reflecting coatings. Its very helpful for requiring contrast enrichment otherwise as substitute

for tinted glass like in a C.R.T. monitor exhibit [5, 6].

So many technics are available for reducing reflectance like by a circular polarizer,

reflections can be blocked. To eliminate reflections, a laminated circular polarizer to a

surface could be used, the polarizer transmits the light by one chirality or handedness of

circular polarization. After the polarizer is transformed into the opposite 'handedness',

light can reflected from the surface, that light couldnot pass back throughout the circular

polarizer because its chirality has totally changed like from “right circular polarized to left

circularly polarized”.

An application of antireflective coatings (ARC) is regularly in “microelectronic photolithography”

to facilitate reduce image distortions related with reflections off the substrate surface. Either

before or after the photo resist, so many different types of antireflective coatings (ARC) are

applied and they help to decrease thin film interference and specular reflections.

1.2. Definition of the problem:

Considering the fact that process stability is one of the crucial factors for any type of

photovoltaic application, this point (work) would be differentiate it other research so we

decided to re-look this technique specifically from this viewpoint and developing a

dependable process set which could be used for reliable prototype samples. The paper

describes results of experiments that we have conducted to study the change in

transmission properties of glass over the entire visible wavelength range after chemical

etching and also describes the environment stability analysis of such chemically treated

glass.

1.3 Review of Literature:

A vigorous survey of the literature at national and international level has been conducted and

presented in a concise manner. The survey indicates the following pattern of growth of research

on the subject.

For making solar cell device, typically requirement of glass that is colour less & transparent.

Glass raw materials include certain impurities such as iron, which is a colorant so it has been

found that the use of low iron highly transparent glass is advantageous for solar cell applications

[11].

Generally solar industry use normal toughen glass without anti reflection coating as making

photovoltaic device but it transmittance is very less like 85% to 91% so many method have

develop for making AR coating on glass substrate like acidic treatment [89, 90], surfactant

mixture treatment, polymeric film coating, sol-gel process, chemical leaching process. According

to Lindmayer (1976) removing metals with enrichment by silicon dioxide process and applied

metal oxide coating during manufacturing of cell, by applying a colloidal dispersion derived from

hydrolytically condensing in the presence of water & catalyst, by creating textured glass surface.

Transmittance of glass substrate also increases by dip coating of mono disperse silica solution

and by developing aluminum surface mirrors [48].

According to Elmer (1977) removing a siliceous surface layer from the glass by heat treatment

at 630°C to 660°C and after than prepared an aqueous solution which containing both hydrogen

ions and fluoride ions, and than treating the glass substrate with for a time sufficient to produce

the antireflective layer.

Formed a porous layer on a surface of a body of phase separable glass through heat-treating

the glass substrate to reason it to become separated in to at least two distinct phase of different

solubility. When a body surface is subjected with a leaching solution, which leaches at least

most soluble phase rather than the least soluble phase, disposed on a substrate of phase-

separated glass. After than second heat treatment is more require at sufficient time that the

glass substrate cause to become homogeneous and the porous surface layer remaining

substantially unaffected or unchanged. The consequential homogeneous glass substrate is

more chemically durable rather than in the phase-separated stage [9].

Minot (1978) also describe anti reflective layers on phase separated glass it formed by glass

heat treatment than it become divided in to at least distinct two phase of different solubility. A

body surface leaches first and than leaching solution preferably contains an acid that etches the

structure of skeletal that becomes so customized, and having antireflection properties.

Glasses which having huge amt of Pb or Ba; early work was performed almost entirely on that.

Glass substrate which having only silica, earth metals & borosilicate were not appropriate for

chemical treatment.

According to Nakajima (1987) this anti reflecting coating can be formed by treating the glass

substrate with an aqueous solution containing specific amount of an acidic salt, Al3+ and Si4+.

For removing metal ions particularly sodium, potassium, or aluminum ions from the glass or

ceramic materials with enrichment by silicon dioxide [91], the items being subjected for a pre

specified time to a plasma- low pressure plasma or corona discharge induced plasma,

hydrogen, nitrogen or a noble gas being used as discharge gas.

To improve the chemical and mechanical durability of coating of antireflective metal oxide is

heated to a temperature below the strain point of the substrate for a sufficient time to anneal the

coating without affect the substrate [25].

According to Becker (2006) treated the soda-lime glass with an aqueous solution having a pH

value of b/w 3.0 to 8.0 and containing b/w 0.40 and 6.0 wt.% of [SiOx (OH)y] n particles having a

particle size of between 10 and 60 nm, and a surfactant mixture. The coated glass is then dried,

thermally hardened at 6000C temperature [8].

An antireflection coating making also use sol-gel dip coating process in this process forming a

silica sol-gel by mixing the polymeric component with a colloidal silica; casting the mixture by

spin coating to form a pours silica based layer on a substrate; and curing or heat treating the

layer [92, 93]. To get better its potency, the silica may be exchange with “zeolite”, that is micro

porous alumino silicate crystalline material. The aluminum chloride barrier layer also applied at

a desirable glass temperature to reduce sodium leaching or diffusion from the glass during

conditions such as high heat or high humidity [11].

Additionally drop in reflectance is affected by deep the substrate in porous aluminum oxide thin

layer in hot water. Using complex silica solns of “fluosilicic acid” to make anti reflective layers on

optical crown glasses and soda lime glasses. Recently surface modification process on anti

reflective coating glass developed by immersing in “hexamethyldisilazane (HMDS)” for

increasing durability of film but all those exist technology not accomplish following condition

essentially requirement for solar module glass like environmental stability of process as per IEC

61646 standard, not established proper process condition, not optimize the optical

characteristics of glass and not also is cost efficient. According to Sanduja (2000) develop a

polymeric coating on glass substrates via chemical grafting for improving antireflective

properties with fight to abrasion, UV degradation & resistance to environmental conditions such

as humidity and corrosive gases. Monomers or pre polymers, catalyst, and graft initiator are use

for chemical grafting. This coating could reduce the reflectance [7].

Becker (2006) developed anti reflection coating on soda lime glass substrate by using sol gel

method so particle size and pH of aqueous solution are play very important role. For

experiment, aqueous coating solution having a pH value of between 3 and 8 and containing

between 0.5 and 5.0 wt. % of [SiOx(OH)y]n particles (0<y<4 and 0<x<2) having a particle size of

b/w 10nm and 60 nm, and a surfactant mixture. The surfactant mixture has 15 wt. % to 30 wt.

%anionic surfactants, 5 wt. % to 15 wt. % non-ionic surfactants, and less than 5 wt. % of

amphoteric surfactants. The coated glass is then dried, thermally hardened at temperatures of

at least 600° C for several minutes, and thermally tempered by a flow of air. The Si02 layer

advantageously has a refractive index (RI) of 1.25 to 1.38 to make a thermally tempered glass

or safety glass, which is provide with an abrasion-resistant antireflection (AR) coating whose

refractive index (RI) is in the 1.25 to 1.40 range. Coating the glass with an aqueous coating

solution and a surfactant proper mixture to forms the silica Si02 layer. The aqueous coating sol

having a pH 3.0 to 8.0, containing 0.5 wt. % to 5.0 wt. % [SiOx(OH)J,]n. where as 0<y<4 and

0<x<2, the particles having particles size of 10.0 nanometer to 60.0 nanometer. Methods also

include drying the coated glass, thermal toughening at temperatures of at least 600°C, and

thermal tempering of the coated glass by a forced airflow. The silica Si02 layer profitably has a

refractive index (RI) of 1.25 to 1.38, the residual reflection of the coated glass substrate or pane

being less than 3.0%, in particular approx 1.0% of the entire glass, while an uncoated glass has

a reflection of approx 8.0%. The present invention also provides a method of developed a safety

glass that includes coating a glass with an aqueous coating solution and a surfactant mixture so

as to provide a coated glass. The aqueous coating sol has a pH of 3.0 to 8.0 which containing

0.5 wt. % to 5.0 wt. % [SiOx(OH)J,], particles, where 0<y<4 and 0<x<2, the particles having a

particle size of 10 nanometer to 60 nanometer. The method also includes drying the coated

glass, annealing the coated glass at temperatures of at least 600°C. for a period of 2.0 to 10

min, and tempering the coated glass in dry airflow. For this point, a standard soda-lime glass

substrate in particular is coated with an aqueous coating solution having a pH value 3.0 to 8.0,

containing 0.5 wt. % to 5.0 wt. % [SiOx(OH)J,]n particles having a particle size of 10nm to 60

nm and a surfactant mixture, where 0<y<4 and 0<x<2. Letting it rest at room temp or dries the

coated glass by drying in an airflow. The dried glass is annealed at least 600°C temperature.

For a period of 2.0 min to 10 min and the heated glass is evenly tempered on the surfaces on

both sides in airflow to reach the tempering effect. The stability of the sol is max. Hence, its not

expected that the solution have sufficient stability at a pH > 3. It is known to facilitate the

property of materials obtain by sol gel methods are extremely dependent on the pH. [8].

Sharma (2008) also developed method of making ARC on glass for application in a solar

module. For this purpose using a sol-gel process. The method include following steps like

forming a polymeric component of silica by mixing glycycloxy propyl trimethoxy silane (or other

suitable silane) with one or more of a first solvent, a catalyst and water. Forming a silica sol gel

by mixing the polymeric component with colloidal silica, optionally a second solvent and at least

one organic additive; casting the mixture by spin coating to form porous silica based layer on a

substrate; and curing or heat treating the layer. This layer may make up all or only part of an

anti-reflection coating. Making a photovoltaic device on glass substrate with anti reflecting

coating which containing porous silica, which may be produced using a sol-gel process

including organic additives like aliphatic or cyclic organic compounds. Glass substrate is an

essential element of most common solar module or photovoltaic modules in which including

crystalline and thin film types. Anti reflecting coatings formed by using a sol-gel process, which

are based on porous silica containing organic additives. This porous silica layer may have high

transmittance (%T), in that way increasing the efficiency and power of the photovoltaic device.

An anti-reflection coating, which is use in a photovoltaic, is making by forming a polymeric

component of silica by proper addition or mixing at least a silane with one or more of a first

solvent than a catalyst and water. Forming a sol-gel solution by mixing the polymeric component

with colloidal silica and optionally a second solvent and at least one organic additive. Casting

the mixture by spin coater to form a layer on a glass substrate and curing or heat-treating the

layer, which are the part of the anti-reflecting coating. The organic additives, which used for

making the porous silica layer, are advantageous in that they allow the resulting density of the

final layer to be decreased. These additives permit to the materials of porous silica based layer

to react in an unknown manner in order to help the silica of the layer increase coupling b/w silica

particles. In addition, it’s noted that the organic additives may burn out through heat treatment

so that they need not be in the final porous silica based layer. The 1st layer of ARC 3 having a

width approx 115 nanometer to155 nanometer. In addition, the refractive index (RI) and material

composition of the first layer may vary throughout the layer in either a continuous or non-

continuous manner in different example. The resulting glass has transmittance (%T) minimum

75%, additional if possible 81%, and most if possible of minimum approx 92%. A polymeric

component of silica prepared by using of n-propanol 64% wt, Glycycloxyl propyl tri methoxy

silane 24% wt, water and of hydrochloric acid 5% wt. These ingredients mixed for 24 h and the

coating solution was prepared by using polymeric solution 21% wt, colloidal silica 7% wt in

methyl ethyl ketone and n-propanol 72% wt. This was proper stirred for 2 h to give silica

solution. The silica coating was fabricated by spin coating with 1000 rpm for 18 seconds. The

coating was cured at temperature 130° C. for 1 min, and then heat-treated in muffle furnace at

625° C. for 3.5 min. [9].

To reduce sodium leaching or diffusion from the soda-lime silica glass substrate during heat

treatment such as thermal tempering or humidity for improving the durability or stability of the

treated glass substrate so for a major surface of the glass is treated with aluminum chloride by

using flame deposition or combustion deposition process. Thereafter, an antireflective (AR)

coating may be applied on the substrate over the aluminum chloride based layer via a sol gel

technique. On uncoated glass, the sodium upon reaching the surface may react with water or

the like to produce visible stains or smears on the glass surface. Moreover, sodium diffusion into

coatings on the glass can damage the coatings thereby leading to defected coated articles. A

soda-lime-silica glass is coated with aluminum chloride by using a flame deposition or

combustion deposition process. After that, an antireflective coating applied on the glass

substrate in excess of the aluminum chloride based layer via a sol gel technique. The presence

of the aluminum chloride deposited, found to decrease sodium leaching or diffusion from the

glass during heat treatment such as thermal temper or the like. Float glass is usually soda lime-

silica based glass and when coated it with an anti reflecting coating or the like is susceptible to

damage as a result alkalis such as sodium diffusing externally from the glass to the surface and

probably into coatings such as anti reflecting coatings or low-E coatings provided on the glass

substrate. This leaching of sodium outwardly from the glass substrate may take place during

heating treatment such as thermal tempering of the coated article in environmental conditions.

On uncoated glass substrate, the sodium upon reaching the surface may react with water to

produce visible stains or smears on the glass surface. In addition, sodium diffusion can damage

the coatings thus leading to defected coated articles. Monolayer anti reflecting coatings applied

on soda-lime-silica based glass. Sodium ions (Na+) in the glass over time when subjected to

high temp and humidity conditions such as those used in accelerate aging tests and thermal

tempering its migrate to the surface. The resulting increases in alkalinity, which cause corrosion

on the coated article surface. The presence of aluminium chloride in barrier layer blocks or

greatly reduces sodium migration from the substrate. This is especially the case when the

aluminum chloride layer is applied to a hot glass surface of substrate, such as when the glass

surface is at a temp at or above Tg. Consider the following chemical reaction like AlCl3 + Na+ +

H2O = Al+++ + NaCl + HCl (e.g., non-stoichiometric). The AlCl3 on the surface of the glass

creates a chemical reaction between the Cl from the AlCl3 and alkali elements like Na or K or

alkaline earth elements like Ca or Mg from the glass. For example Na2O of the glass matrix may

react with Cl- from the AlCl3 to form NaCl (NaCl = Na+ Cl) and the oxygen O2 may be removed

as an oxychloride or the like HCl or water H2O can be removed in form of vapor. In a related

manner, K2O of the glass matrix reacts with Cl- from the AlCl3 to form KCl. As another example

like CaO of the glass reacts with Cl- to form calcium chloride CaCl2. Therefore, it will be valued

that treatment of the glass surface with aluminum chloride is an efficient technique for reducing

the ability of alkali or alkaline earth elements to leach out of the glass and stain the surface

thereof or damage a coating thereon like during heat treatment such as thermal tempering [10].

For improving transmittance on glass substrate, Fulton (2009) making patterned on it. So for

providing a molten glass batch in a furnace or melter comprising SiO2, total iron, salt cake,

lithium oxide, and antimony oxide than refining the glass batch. After processing patterned glass

having a visible transmission of at least 90%, about 0.01 to 0.06% total irons, about 0.25% to

3.5%lithium oxide, about 0.3% to 0.4% salt cake, and about 0.01 to 1.0% antimony oxide. The

use of a low-iron highly transparent glass is advantageous for solar cell or photovoltaic

applications. The use of the low-iron composition in combination with the patterned surface of

the glass found to be advantageous with respect to optical properties, thus leading to increases

solar efficiency of a photovoltaic or solar cell. A method of making patterned glass by providing

a molten glass batch in a furnace comprising silica SiO2, from about 0.01% to 0.06% total iron,

salt cake, lithium oxide, and antimony oxide. Refining the glass batch wherein the batch has a

seed free time of less than 100 min, forwarding a glass ribbon from the furnace to nip b/w 1st

and 2nd rollers. At least one of the rollers having patter defined in a surface thereof, wherein the

glass ribbon reaches the nip at a temperature 1,900°F to 2,400°F.; at the nip, transferring the

pattern from the rollers to the glass ribbon; the glass ribbon being at a temp of from about

1,100°F to 1,600°F. upon exiting the nip; and annealing the glass ribbon at least after the ribbon

exits the nip, thereby provided that a patterned glass having a visible transmission (T) of at least

90%, from about 0.01% to 0.06% total iron, from about 0.25% to 3.5% lithium oxide, from about

0.3% to 0.4% salt cake, and from about 0.01% to 1.0% antimony oxide. A soda-lime-silica

based low iron highly transmittance glass, use in a photovoltaic device, the glass has visible

transmittance of at least 90%. The method comprises providing the lithium oxide, antimony

oxide and salt cake in the recite amounts in a batch in making the low-iron glass so that a seed

free time in making the glass substrate is no more rather than 100 min. One or both major

surfaces of the glass substrate may be patterned. Light tends to be refracted at interfaces

resulting from the patterning of the glass. Thus causing light to proceed through the

semiconductor layers at an angles such that the path is longer as a result more light absorbed

by the photovoltaic cell or solar cell and output current efficiency can be increases. The

patterned surfaces of the glass substrate have a surface roughness of from about 0.1 to 1.5

micrometer. The glass substrate has one or more surfaces, which are patterned so as to having

a waviness characteristic defined therein. The use of antimony Sb in the form of antimony oxide

Sb2O3 as an oxidizer in the glass batch acts as a decolorizer. This antimony role as an oxidizer,

which decreases the amount of ferrous state iron, left in the resulting glass substrate. Due to the

presence of antimony oxide in the glass is causes an amt of the strong blue-green colorant of

ferrous iron Fe2+, FeO to oxidize into the yellow-green ferric iron colorant Fe3+ through the glass

melt. The oxidation of the iron tends to decrease coloration of the glass and also the causes of

increasing to visible transmission. Any yellowish color due to the oxidation of Fe2+ into Fe3+ iron

(i.e. positive color value b*) is acceptable in solar cell or photovoltaic applications. Ingredient

require in low-iron highly transmissive glass which are use in a photovoltaic device or solar cell

are by wt. % SiO2, 67% to 75%, Na2O 10% to 20%, CaO 5.0% to 15%, total iron (as Fe2O3)

0.001% to 0.05%, cerium oxide 0 to 0.07%, antimony oxide 0.01% to 1.0%, lithium oxide 0.25%

to 3.5%, salt cake 0.30% to 0.40% in which the glass having visible transmission of at least 90%

and in which the method providing the antimony oxide, lithium oxide and salt cake in the recited

amounts in a batch in making the low-iron glass so that a seed free time in manufacture the

glass is no more rather than 100 min [11].

Per Nostell, Arne Roos and Björn Karlsson (1998) make fairly high quality anti reflective film

with the used of silica sol dip-coating process. According it two sols was investigated, one poly

disperses and one mono disperses. This method has several capable properties, like high

deposition rate. Prepared films havings outstanding optical characteristics. One drawback of this

method is related with mechanical properties for improve it bake the film at approximately 500º-

550ºC during approximately 30 min In this experiment for process of dip coating, water (25 ml),

ethanol (90 ml), methanol (80 ml) and hydrochloric acid (0.5 ml) were proper mixed. Their

experimental results solution in a certain interval control by pH value [12].

Anti reflection coating also developed on low iron glass support the hypothesis of higher

porosity for monodisperse sols. The stability of the substrate, the size of glass substrate is 10cm

X 10 cm to 1m X 1m. To develop efficient broadband antireflecting layer for transparent cover

or layer, we require RI approx 1.5 also single-layer, gradient RI for antireflective layer is more

effective from the 0.35 to 2.5 micrometer [13]. Coated sample heated at approx 500o C for 10 to

15 min. New solutions developed by organically modified alcoholic solutions and possess a

shelf life time of 01 year also developed water-based solutions. Between 5.0 cm/min and

150cm/min., withdrawal rates also varied. After completion of the coating, the samples were

proper heat in a furnace at temperatures of 500°C for 10min to 15min. Periodic master

structures developed with holographic exposure of photo resist. The highest value of the solar

transmittance was also prepared by physical vapour deposition [14].

Dinguo chen (2001) review the development and characteristics of sol gel derived AR coating

on different substrates for a range of applications and also compare the study of major coating

processes used in ARC technology like dip coating, spin coating, meniscus coating [15-17].

To increase the visible transmittance of a low-emittance (low-e) glazing by antireflection

treatment, Elin Hammarberg and Arne Roos (2003) carried out it by depositing thin porous films

of silicon dioxide (SiO2) on both sides of a commercial glazing by SnO2 coating [18,19].

Mazurin O. V. (2005) described the glass structure and their properties and also mentions the

various examples for binary glasses [20, 21].

Bunte, Eerke, Zhang, Wendi, Hupkes and Jurgen (2010) described an up-scalable method to

create a variety of randomly nano textured surface features on glass substrate. The topography

of texture etched ZnO films was transferred to glass substrates by ion beam etching. According

to it vertical and lateral sizes of the glass feature can be adjusted in a certain range by varying

initial ZnO film thickness and wet-etching time. The developed glass textures show good light

properties. For microcrystalline silicon cells, an improvement of short circuit current of up to 36%

was achieved. For the fabrication, an aluminum doped zinc oxide (ZnO) layer was developed on

glass substrates. Frequency radio magnetron sputtering from planar ceramic targets is with 1

wt. % aluminum oxide content. A low sodium glass type Corning Eagle XG used to avoid effects

with sodium migration. Films with thickness of 800nanometer and 1500nanometer were etched

for different times b/w 30seconds and 330seconds in 0.5wt. % hydrochloric acid. The process of

IBE carried out by an anode layer ion source with argon gas. The mean incidence angle of the

ions varied b/w 0°C and 40°C toward the normal substrate. The IBE process was carried out till

the zinc oxide film was completely removed. The ion source was operated at max voltage of 3.0

kilovolt, high argon gas flow of 40 SCCM where SCCM denotes cubic centimeter per minute at

STP and pressure of 1.0 x 10−3 mbar to achieve highest possible sputtering yield. Zinc oxide

(ZnO) and glass are removed with etch rates of 6 nm/min and 5.4 nm/min at that conditions of

an ion incidence angle of 40°. Atomic force microscopy for samples were carriedout before and

after the IBE process to examine the evolution of the surface morphology [22].

Anti reflective coating also developed with silica sols of 20 nm average particle size.

The solution ready by silica solution, HNO3 used for pH correction and propyl alcohol

used as solvent. The wt% of silica is 3.6 [23].

“Porous silica layer” are widely used for solar collector glass as a anti reflecting layer or

coating [24-29]. Thickness of the coating and solar transmission for SiO2 film of nano

particles approx 10 nanometer, heat at temperature 773°K, than sintered it. The solar

transmittance (T) is decreases with decrease in thickness (d) of the film. The

transmittance of ARC heat at temperature 773°K, was found 97.5% with coating

thickness of 111 nanometer [30]. Environment chamber or weathering conditions effect

or treatment carried out by Vicente [31] and only sintering related experiment carried out

on porous silica coating on glass substrate by Glaubitt [32]. The avg transmittance data

from 300nanometer to 2500nanometer weigh with the air mass is 1.5. Transmission

max at 550nanometer heated at temp 773°K was the high E98.6% where as the sample

heat at temperature1423°K transmits only 92.8% comparison to the without coated

silica substrate [33].

For improving strength of anti reflecting coated glass substrate so according it

amorphous SiO2 [34-37] replace by zeolite. Hybrid solution also used by Glaubitt for the

preparation of abrasion resistant silica (SiO2) antireflection (AR) coatings [38].

Antireflective silica coatings also assembled by Prevo B.G. with controlled coating

thickness and RI [39]. ARC with scatter surface texture formed only by changing

crystalline zeolite. Zeolite is a microporous aluminosilicate crystalline materials and its

use for making scratch resistance anti reflecting coating on glass substrate. Scratch-

resistant ARC making by a soln, that having zeolite nano particles as the structure

provider & precursors [40, 41].

Anti reflection coating develop on glass substrate for solar application [42] by using sol–gel dip-

coating process of nanoporous solution of ZnO/SiO2 than characterized the structural,

morphological and optical characteristics of single layer and bilayer coatings. The broadband

antireflection performances of ZnO/SiO2 bilayer coatings are established. For making of zinc

oxide and SiO2 precursor solns chemical reagents purchased from Sinopharm Chemical

Reagent Company. Zinc acetate dihydrate and Diethanol amine (HN(CH2CH2OH)2) dissolved

or proper mix in ethylene glycol mono methyl ether at room temp. Now the soln was proper

stirred at 65°C for 2.0h to yield a uniform zinc oxide precursor sol with a concentration of 0.75

mol per L. The silica solution now synthesized using tetra ethyl ortho silicate as a precursor,

NH3 as a catalyst and C2H5OH as a solvent in a molar ratio of 1:2:40. After developing of

precursor soln now prepared ZnO/SiO2 coatings by using dip coating process at a speed from

3.0 to 200 mm/minute [43].

Thin layer like tarnish on the glass could be increases the transmittance, it’s observed by Lord

Rayleigh, this cause could be defined by envision a thin layer of material with RI b/w the glass

and the air [44].

San Vicente G., Bayón R., Germán N., Morales A. (2011) studied the purpose of a surface

modification procedure for increasing the strength of the anti reflective films. If the film surface is

customized exchanging the active OH- grps by inert “organosilyl grps” [45].

Silver first surface mirror is used for solar energy application but commercially its cost is very

high, silver first surface mirror having minimum four layers to obtain a high-quality adherence

[46, 47]. Almanza using Si203 and SiO as the front surface film, over Al films The using mirrors

size is 30 cm × 30 cm with a 3-mm thickness substrate. During 20 min (3 kV and 250 mA), a

glow discharge produced which clean substrate. After cleaning the mirrors, an aluminum film

was deposited on it. There are 02 types of 1st surface mirrors were created. No degradation

was detected after one year of exposure to the environment but after two years a slight

corrosion appeared [48].

Angadi (1989) develop a heat mirrors by using CeO2/Cu/CeO2 multilayer films. Heat mirrors

having high %T could be found by using semiconductor mat which illustrate high IR reflectance

[49]. Also investigated in this paper the effect of substrate temp and in situ annealing on optical

property [50, 51].

Gombert A. and Glaubittb W. developed low coast sub wavelength structured broad band

antireflective layer on glass substrate and on plastics by using sol-gel dip coating on glass. The

trial carried out on low iron content glass substrate, the area of glass substrate is from 10 x 10

cm2 to 1 x 1m2. Before experiment clean the low iron glass substrate by alcoholic solution [52].

To obtained scratch resistance with compare to polymer in glass, plastic & metals by using

“ORMOCER” layer or film as a patternable materials [53, 54].

Gradient index antireflecting coating developed with sol-gel procedure [55] and also another

process to develop ARC for solar use are depend on the theory of mixing bulk mat through air

on a sub wavelength scale [56, 57]. These are achieving with porous media & sub wavelength

surface-relief gratings [58]. It’s shown that an increase of transmittance of approx 3% per glass

surface, achieved with a porous sol-gel coating. For developing porous sol-gel coatings,

samples prepared by using dip coating process on low iron content glass substrate [59].

To increase 20% energy created in a solar system by using ARC on the solar glass [60]. Solar

transmittance values increase by deposited sol–gel silica porous coatings on borosilicate glass

also the studied densification process of the films and the optimal heat treatment conditions

established. For preparation of solutions mixed tetraethyl ortho silicate, water and ethanol in the

molar ratio of 1/5.1/48. Used HCl as a cat. for obtain acidic environment. Than proper stirring for

23 hrs, “Triton X” add at conc of 31.0 gm per liter as a pore generator. Added Methyl tri

ethoxysilane (MTES) to take the ration of “TEOS / MTES” to 80.0% / 20.0%. By dip coating, the

layers were coated on 2.5 mm thickness on the borosilicate glasses. The size of borosilicate

glass is 70×40 mm. At various temp coated samples were instantly heating at different time

interval. The films layers were made to order to be hydrophobic by dip them in a

“hexamethyldisiloxane” soln for 24 hrs. For characterization of sample total direct transmittance

spectra measured at room temperature by using a UV/VIS/NIR [61].

Different texturing process or methods [62, 63] and single or multilayer ARC develops for

silicon interfaces [64, 65]. To prevent reflection from solar panel with mechanical tracking, the

trouble of dust gathering more time antireflective coatings could exacerbate it [66]. In this

process a non-lithographic nano structuring of the packaging glass surface is exposed. For

fabrication process used Boro float glass substrates. During fabrication 1st developed thin layer

of Ni on substrates [67].

Antireflection coating also developed by using dip coating of SiO2/TiO2. The avg transmission

(%T) of glass coated is raised by > 5.0% in the w. length range from 400nanometer to 800

nanometer. To make porous silica anti reflecting coating, colloidal process with basic hydrolysis

is broadly used for that [68, 69]. The mechanical presentation & environment tests of developed

layer glass substrate confirm that the layer having scratch resistance [70]. SiO2 precursor sol

was “teraethylorthosilicate (TEOS), its mixed with ethanol also add DI water for hydrolysis and

HCl as catalyst. Titanium oxide (TiO2) soln ready from tetrabutyl titanate, mixed with C2H5OH,

DI water for hydrolysis, acetylacetone as chelating agent and CH3COOH as catalyst for two hrs.

The silica oxide (SiO2) and titanium oxide (TiO2) coating than coated on the glass from that

solns [71].

For making superhydrophobic, transparent coating or layer on glass substrate, using sol gel

method by Tadanaga [72, 73]. On soda–lime silica glass substrates, antireflective properties of

flowerlike alumina thin films prepared by the sol–gel method with treatment of hot water. For the

reflection measurement a mirror on which aluminum was deposited used as a reflector. The

reflectance was analyzed from one side. The other side ground of substrate, painted and

covered with black tape to avoid backside reflection [74].

According to Sameer the fabrication, design, & categorization of a broadband, omni directional,

graded-index ARC making by nanostructured low RI like RI=1.05–1.40 silica by oblique angle

deposition [75].

Nanoporous organosilicate films may be used as antireflection coatings (ARC). By the

sacrificial-porogen approach, nanoporous “poly(methylsilsesquioxane)” films developed and it’s

have been recognized as potential ARCs [76].

To deposit silica nano particle layer or coatings on glass slide and silicon substrates

assemblage at higher vol portion was used for that. This method making large-scale coatings

with ARC properties with all outstanding control have the film thickness and structure. According

to that, the reflectance was decreased 50.0% for silicon at 600nanometer and 70.0% for glass

or air surface. Micro structural analysis carried out by instruments like profilometry, AFM, SEM,

and ellipsometry and they provided good relationship to the observed macroscopic optical

property. During trial silica nanocoatings were making with proper dispersions of silica

nanoparticles of “74 (14 nanometer in diameter (%solids 5.670), 134 (25 nanometer (%solids

5.420), and mixtures of both particles”. In the mixed particle coating, different vol fractions of “74

nanometer silica and 64 (12 nanometer sulfate stabilized polystyrene nanoparticles (%solids

2.6)” were deposited [77].

Broadband and low-cost ARC essential for photovoltaic solar cell approx 100 nanometer

thicknesses making by using a dip coating method where silica soln used as precursor could

raise the transmission oat glass substrate up to 98.0%, though, contact of the substrate to

ambient conditions to an aging by succeeding loss in their transmittance. Investigated aging

methods revealed that there are 02 overlap mechanism that is in a quicker procedure through a

reaction time of days, in this process residual sodium ions from the silica sol reacted with H2O or

carbon dioxide from the air and another in a slower procedure through a reaction time of

months, calcium (Ca+2) ions disperse from the float glass in to and form the products like

calcium carbonate. The RI of silica coating is raised and the pores are filled in both type of

process. During the trial the starting material the silica solns 01 stabilize with sodium hydroxide

(NaOH) with an Na2O which content of 1850.0 mg/liter the particle dia is 15 ± 20 nanometer and

solns 02 stabilized with ammo hydroxide (NH4OH) and Na2O content 650.0 mg/liter the particle

dia 20 nanometer, 2-propanol and 1.0 normal nitric acid. By using atomic absorption

spectrometry, Na2O contents analyzed. The conc of oxide in the solns amounted to 3.40 wt%

through a PH range b/w 1.0 & 2.0. Experiment carried out on float glass 03 & silica glass and

also polished silicon wafers used as a substrate for the elliptometric analysis of the RI [78].

Glass coating with silica and than titanium oxide by dipping in to solutions that’s making by 02

diff process involving complex development & hydrolysis, using C2H5OH or butyl glycol. Conc of

TiO2 in solns kept at 0.1% of wt and 0.4% of wt. Developed layer was examine by “field-

emission scanning electron microscope (FESEM), UV–Vis Spectrophotometer, atomic force

microscope (AFM), haze meter and goniometer”. “Rhodamine B” photo degradation test was

also perform to assess photo catalytic activity [79].

AR nanometric SiO2 films were developed on glass by dip coating procedure. SiO2 soln having

an avg particle size of 10 nanometer. SiO2 sol was making with hydrolysis & polymerization

reactn of “tetra methyl ortho silicate” in presence with nitric acid catalyzer. A particle size

analyzer inst. determined particle size of the SiO2 soln. Dipping its in SiO2 soln and withdraw at

“100, 125, 150, 175, 200 mm/minute” speed, coated 4 mm thick, 10 cm x 15 cm soda-lime

glass. After drying, the coated glass baked at temperature 300°, 350°, 400°, 450°, 500°, 550°C

for 60 minute [80].

Diff. RI bilayer thin film was making by placing a higher RI layer with a RI of 1.450 lower the

nanoporous thin film. For that a “poly (methyl silsesquioxane)” copolymer as a matrix material to

distinguish nanoporous thin films developed by the sol gel reaction with “1,2-

bis(trimethoxysilyl)ethane) BTMSE” & “methyl tri methoxy silane (MTMS)”. The BTMSE &

MTMS feed ratio was 10:90 by mol %, a tetra-functional block copolymer- Tetronic 150R1

worked as porogen [81].

ARC also making by the Layer-by-Layer deposition procedure & postcalcination for that

complexes of “poly (diallyldimethylammonium chloride) (PDDA)” and “sodium silicate (PDDA-

silicate)” are alternately deposited by poly acrylic acid (PAA) to fabricate PAA/PDDA-silicate

multilayer films [82].

Novel low RI fluorinated polymers also making with “perfluoroalkylsilane and

polyethoxysiloxane” by a sol-gel procedure for ARC applications [83].

Mono dispersed silica colloids with Ca. 380nanometer diameter are prepared by the “Stober

method” [44, 45]. Silica colloids are purified in 200-proof ethyl alcohol & then redispersed in

“ethoxylated trimethylolpropane triacrylate monomer”. “Darocur 1173 (1.0wt %) (2-hydroxy-2-

methyl-1-phenyl-1-propanone)” is added as the photo initiator [84].

A subwavelength structured surface for broadband ARC purpose is designed & made-up by

micro-replication procedure combine with the originated structure manufacture realized by

interference lithography, Ni mold electroplating and replication by with UV imprinting into

plastics [85].

Poly (propylene glycols) used as effective additives to the Sol-Gel Process in fabrication of

Antireflection Coatings onto Silica Glass. During experiment, possibility of obtaining

mesoporous silicon dioxide antireflection coatings with low refractive index (1.20–1.277) by

using additions of poly (propylene glycols) with a range of molecular masses in a sol-gel

process was examined. It was demonstrated that the optimal concentration of poly (propylene

glycols) in the solution, at which a sol-gel process followed by heating of a sample yields a

transparent film with a maximum light transmission of 98.3% to 99.0%, depends on the average

molecular mass of the additive. Poly (propylene glycol) oligomers (MM 425 to 3500) can be

used as an organic additive to a silicon dioxide solution, which predetermines spontaneous

micro separation of the inorganic and organic, phases in the formation of a gel as a thin

transparent film on the silicate glass surface. In “burning-out” of the organic phase from the gel

at temperature 500°C in air, a transparent film of nanoporous silicon dioxide is formed on the

glass surface [86]. The film has a low refractive index 1.20 to 1.277 and exhibits a strong

blooming effect. The organic additive has the optimal concentration of 2.0 wt % to 3.2 wt % in

the solution. The refractive index (RI) of nanoporous silicon dioxide films decreases from 1.277

to 1.20 and the optimal concentration of the additive grows from 2.0 wt % to 3.2wt % as the avg

molecular mass of polypropylene glycol increases from 425 to 3500 [87, 88].

Before developing antireflective coating on glass substrate, pretreatment must require so strong

acids like nitric acid or sulfuric acid is best suitable acids for this purpose [89, 90].

1.4. Objectives:

PV producers have a strongly demand for high transmission glass. Glass is desirable for some

optical characteristics like transmittance, reflectance, and absorption are desired to optimize.

The objective of the present work is to develop an anti reflecting coating on glass substrate,

which would be good transitivity, environmentally stability, good heat stability, easy and cheap

to produce. All those entire criterions would be fulfills by the chemical etching of glass substrate.

Simply due to apply chemical treatment process on glass substrate we can achieved overall an

increase of transmittance on both side of glass substrate as well as Environmentally stable

chemical layer.

It is proposed to carry out the work with the following specific objectives-

• To increase transmittance of glass substrate.

• Optimizing the optical characteristics of glass substrate.

• Determination the pH value of anti reflecting coating solution.

• Transmittance value interpretation by using UV-VIS spectrometer.

• Establish the process condition.

• Process stability identification.

• Confirmation of environmentally stability as verified through IEC 61646 standard.

• Determine the top layer textured of treated and untreated glass by using instrumentation

like Atomic force microscope (AFM).

• Making photovoltaic modules using treated glass substrate and check efficiency of

photovoltaic modules.

• Calculation of Pmax and Isc after preparation of photovoltaic modules.

1.5. Importance of the proposed work in the present context:

Anti-reflective coatings a new wave of anti-reflective technology is emerging with some of the

most promising products in development having multi-functional properties that could benefit

solar PV cover glass. Research groups around the world have been using the principal of

moths’ compound eyes that do not reflect incoming light, as the basis for developing highly

efficient anti-reflective solar glass coatings. Inspiration from lotus leaves – which repel water –

and moth eyes to develop a method of producing glass with anti-fogging and self-cleaning

properties combined with low reflectivity. Such glass has a broad range of applications including

lenses for cameras and microscopes suitable for even the most humid conditions and smart

phone touch screens as well as AR solar glass. Anti reflection coating produce a surface

covered with tiny cones, each five times taller than their width of about 200 nm across. The

pattern both prevents reflections and repels water from the surface. This could result in a dual

functioning PV cover glass able to help maximize module output. The glass is able to keep itself

clean of dust and dirt and also absorb more light, especially during times of the day when the

light hits the panel at a sharp angle of incidence, known as broadband omni directional

transmission.

An elegant way of reducing the cost of electricity generated by a typical solar PV power plant

would be to make panels more productive whilst decreasing maintenance costs. That pushes

down the levelized cost of electricity (LCOE), which not only takes into consideration initial

capital expenditure (CapEx) but also the costs of continuous operation, maintenance and other

associated expenses over an energy plant’s lifetime. This could be achievable in future as a

new generation of smart coatings that combine anti-reflective (AR) with self-cleaning properties

becomes commercially mature. Anti-reflective coatings (ARC) for solar glass have a significant

boost on a PV panel’s ability to turn sunlight into electricity. They work by reducing the

reflectivity of glass, allowing more light to pass through, increasing the energy output of modules

by a few percentage points.

The embodiments of the invention are directed to anti reflection coatings and their uses. ARC is

necessary to avoid optical losses and increase the current of the solar modules. More

particularly, the embodiments of the invention are directed to coating compositions. The

coatings so formed are characterized by anti-reflective, abrasion resistant, and anti-soiling

properties. The coatings also have extended weatherability to heat, humidity, and protection

against ambient corrosives. The coatings formed from the compositions described herein have

wide application, including, for example, use as coatings on the outer glass of solar cells. The

anti-reflective coating (ARC) increases solar cell performance by reducing the amount of

reflected.

Depositing nano-porous solid silica particles, or sol-gel, coatings produces the majority of anti-

reflective glass for PV cover glass, as the method is cost-effective and can be integrated into

production lines.

The unprecedented growth of the global PV industry in recent years has encouraged R&D

efforts to develop more advanced AR technologies, some of it now in production.

A recent example is Dutch chemicals producer Royal DSM N.V., which has managed to push

the performance of ARC designed for PV glass with its KhepriCoat technology, by increasing

light transmission by 6%, resulting in 4% more panel efficiency.

ARC coatings for solar glass proves there is lots of potential for advanced anti-reflective glass

technologies, compatible with industrial PV production processes. Many of the most promising

next-generation AR technologies in development also have additional properties, such as self-

cleaning, or anti-fogging.

Soiling and dirt on the cover glass affect PV panel efficiency. Potential energy loss can be as

high as 30% for very dirty panels and can reduce the power conversion of solar mirrors by 40%

or more depending on the thickness of dust and particle layers. For utility-scale solar plants, the

LCOE – which must take into consideration the operations and maintenance (O&M) costs over

a plant’s lifetime – using a self-cleaning solar glass can help reduce the LCOE.

Several independent R&D efforts are using nano technology to develop glass-coating

technologies with multi-functional properties. These can both enhance module output by

reducing the amount of light reflected from the glass surface and prevent the glass from getting

dirty and dusty. Combining these different properties in one material to create bi-functional

coatings, or so-called “smart coatings”, could also reduce production costs as only one coating

product would need to be applied. Researchers at Technical University Clausthal, in Germany,

have examined AR coatings for solar cover glass and photo catalytic coatings for self-cleaning

glass, each based on a different type of nano-functionalized thin film. Broadband AR coatings in

wide use tend to exploit the low refractive index of nano-porous silica, whereas the most

established photo catalytic coatings consist of high refractive index materials, such as titania.

The potential compatibility of these two functional materials was investigated using sol-gel dip-

coating technology.

A bi-functional coating technology improves transmission properties, boosting the annual energy

yield of a PV system up to 6%. In addition, low-iron solar glass treated with the coating exhibits

hydrophilic surface properties, resulting in a degree of self-cleaning.

All components that go into making a solar panel have their price tag, so it makes sense that a

key component such as glass, in addition to its main function of protecting the modules within,

should be engineered, or treated, to do more to maximize panel output. Falling costs in PV

modules and increasing efforts by governments to implement PV at the utility scale, particularly

in sunbelt markets such as the Middle East, will help to drive demand for some of these

advanced bi-functional and multifunctional glass coatings and solutions in the coming years.

Maintaining a solar farm in dusty desert conditions includes keeping panels as free from dust

and dirt as possible. Such smart coatings could help to reduce these costs over the lifetime of

the plant. A PV plant with lower operating and maintenance costs leads to lower LCOE, making

PV cheaper in future.