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 800-1000C 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
chipping
of the uncoated glass

FMEA METHOD USED FOR ARC GLASS

Figure 1: Temporary staining due to plant residue
observed during field exposure of ARC glass
modules 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