Presentation

on

Antireflective coatings

A

PRESENTED BY :-

RAJNEESH KUMAR GAUTAM

M-TECH (ENERGY AND ENVIRONMENT)

IN THE EXPERT GUIDANCE OF :-

VIJAY K. JAISWAL

ASSISTANT PROFESSOR (GUEST)

BBA UNIVERSITY -LUCKNOW

In typical installations,

approximately 4% of incoming

light is reflected off the face of

the PV module and is lost.

ANTIREFLECTION coatings

REFLECTION

coating

What is antireflective coating ?

Antireflective or anti-reflection (AR) coating is a type of optical

coating applied to the surface of lenses and other optical devices to

reduce reflection.This improves the efficiency of the system since

less light is lost.

Antireflection is achieved by destructive interference between

incident rays.

coating

For destructive interference Δ = (2m+1) λ/2

2nd = (2m+1) λ/2 => d = λ/4nc = λ’/4

m=0,1,2,3……………………..

d = minimum required thickness of coating

λ’ = wavelength in coating medium

’

About 4% of the light hitting the glass of a solar modules is reflected and thus

lost for electricity production.

Reflections can be reduced and thus light transmission can be increased by

using antireflective (AR) coatings.

The higher electricity output results in a reduction of the cost per panel.

‘Traditional’ AR coatings are either expensive or have to compromise on the

balance optical vs mechanical properties.

Why use anti-reflective coatings on

solar cover glass?

binder

Glass substrate

“Traditional” AR

coating

Solid silica particles

Glass substrate

Coating layer

(100-150 nm)

Modern Coat™ AR coating

Electro deposition

Chemical coating

Conversion coating

Vapour deposition

Chemical vapour deposition

Physical vapour deposition

Spraying

Back

Formation of antireflection coating

Plasma enhance chemical vapour deposition

Spraying process

CHEMICAL COATINGS

Advantages

Low temperature treatment

More corrosion resistant than electrodeposited chromium

Can coat complex shapes uniformly

Hard particles can be incorporated to increase hardness .

Can coat most metals and some insulators

Disadvantages

More expensive than

electroplated chromium

Heat treatment is needed to

develop optimum properties

CONVERSION COATINGS

Thin compound layers can

be produced by reacting a

metal surface with an

acidic solution. e.g. Thin

(10mm) coatings of metal

phosphates are formed on

steel substrates exposed to

phosphoric acid. These

provide low friction

surfaces.

Advantages

Cheap and simple to

perform

Low temperature

treatment

Disadvantages

Restricted range of materials

can be treated

Thin treated layer

Poor treatment durability

Difficult to control treatment

quality on heterogeneous

materials.

PHYSICAL VAPOUR DEPOSITION

A variety of vacuum deposition

Purely physical process , no

chemical reaction involved.

Process involved three steps:

• Evaporation

• Transportation

• Deposition

multiple coating layers possible

MgF2 coating on glass

Almost any type of inorganic material can be

used as well as some kinds of organic materials.

The process is more environmentally friendly

than processes such CVD.

Advantages of PVD

Disadvantages

High capital cost

Equipment size large because vacuum required

Processes requiring large amounts of heat require

appropriate cooling systems

The rate of coating deposition is usually quite slow

CHEMICAL VAPOUR DEPOSITION

Gaseous compounds react to form a dense layer on a heated substrate. The most widely deposited wear-resistant coatings are TiC, TiN, chromium carbide and alumina. Deposition temperatures are generally in the range 800-1000C which restricts the range of materials which can be coated and can lead to component distortion. Thicknesses are limited to about 10mm due to the thermal expansion mismatch stresses which develop on cooling which also restrict the coating of sharp

edged components.

Layer deposition involves chemical reactions

Large density films

Good stoichiometry & uniformity over large surface area.

SiO2 SiN, SiON, SiOC , and TiO2 with proper thickness are

the common AR material deposited chemically.

Required high temp to produce high quality material and for

many application the substrate cannot tolerate being heated

so not useful in that case .

LIMITITATION :

Advantages

High coating hardness

Good adhesion (if the coating is not too thick)

Good throwing power (i.e. uniformity of coating)

Disadvantages

High temperature process (distortion)

Sharp edge coating is difficult (thermal expansion mismatch stresses)

Limited range of materials can be coated

Environmental concerns about process gases

Combined process of both CVD and PVD

a process used to deposit thin films from a gas state (vapour)

to a solid state on a substrate.

Chemical reactions are involved in the process, which occur after

creation of a plasma of the reacting gases

The plasma is generally created by RF (AC) frequency or DC discharge

between two electrodes, the space between which is filled with the

reacting gases.

Processing plasmas are typically operated at higher pressures

PLASMA ENHANCED CHEMICAL VAPOUR DEPOSITION

of a few millitorr to a few torr , although arc discharges and

inductive plasmas can be ignited at atmospheric pressure

Plasma enhanced CVD is most useful because it can deposit layers on fragile

substrates that cannot withstand the high temperatures of other CVD

methods

Plasma enhanced CVD systems allow for greater control of the film

composition, density, and film stress.

Higher deposition rate at low temperature relatively

Plasma can cause damage to the substrate surface when either secondary

electrons collide with the wafer surface or the energy of the ion bombard-

ment becomes too high.

High cost.

Advantages of PECVD

Disadvantages

How much reflection while using AR coating ?

Can be reduced up to ~ 0.2%

APPLICATION OF ANTIREFLECTION COATING

Anti-reflection coated optical windows

Reflex free sight glasses

Laser scanner windows

Contrast enhancement

Anti glare coated instrument windows

Sensor technology

Low reflection camera windows

Holography components

Antireflection coated glass for displays

In microelectronic photolithography to

reduce image (substrate) distortions .solar cell with SiO coating

Glass with MgF2 coating

TESTING OF ARC SURFACE

SAND BLAST TESTING

Figure 2: Surface defects post sand blasting test,showing scratches on ARC glass and chippingof the uncoated glass

FMEA METHOD USED FOR ARC GLASS

Figure 1: Temporary staining due to plant residueobserved during field exposure of ARC glassmodules in heavy pollen areas in California.

http://en.wikipedia.org/wiki/anti-reflectivecoating

http://www.pgoonline.com/intl/katalog/antireflection.h

tml

http://hyperphysics.phy-

astr.gsu.edu/hbase/phyopt/antiref.html

http://www.rp-

photonics.com/anti_reflection_coatings.html

http://www.guardian.com/oracleprd/groups/guardiando

tcom

http://www.pveducation.org/pvcdrom/design/anti-

reflection-coatings

http://www.eere.energy.gov/basics/renewable_energy/

pv_contacts_coatings.html

Reference links :

THANK YOU