Abstract: a substitute strategy for the non-renewable

Abstract:  Due to the high energy
demands which are followed by the crisis of petroleum, the desire for the
future lies in the renewable energy resources such as solar energy. In Photovoltaic
cells, the mainly used material is Silicon in both crystalline and also
amorphous form for the fabrication and also used in manufacturing industries.
This research paper
gives the overall overview about the materials and also the processes used for
fabricating a solar cell. The aim of this paper is to study the solar cell
fabrication technology and also the fabrication of the solar cells. However,
there are a lot of challenges involved such as high manufacturing costs, energy
conversion efficiency, uniformity, easy handling and storage etc. In response,
solutions have been suggested in terms of both alternatives, manufacturing
methods and materials used in the photovoltaic cells. The paper further
explains in detail about the various fabrication processes utilized in the
modern era. The paper ends with contrasting the various techniques and pushes
the idea of using the most efficient solar fabrication processes.


Solar energy is the energy generated from the
atomic combination in a star, i.e. the sun. The energy is released when the
fusion process takes place. That energy goes through the layers of the sun
until the point when it achieves the surface of the sun, where the light is
emitted. Of the transmitted energy that reaches the atmosphere is known as the
solar constant. Solar panels are made up of solar cells which converts light,
energy, into electric or electricity form. The earth receives more energy from
the sun for just one hour than the world which uses in a whole year. This shows
a very high sun based radiation that should be utilized; as a substitute
strategy for the non-renewable energy sources utilized today.


Solar panel boards which consist of cells
situated together in modules which

mean the solar cells hold a noteworthy part
in the panel’s last execution. In solar market today we use commonly three
sorts of photo voltaic cells; single and, poly-crystalline cells, thin film. Without
any difficulties the cells are separated by their appearance, thin film cells
are sometimes black and even in their shades, single-crystal cells have thick
blue color and poly-crystalline cells have various shades of blue.



The most common
semi-conductive material used in solar cells is silicon where it is important
to separate amorphous (un-structured) and crystalline (ordered) silicon.

Monocrystalline cells: Crystalline silicon solar cells represent
about 90% of the PV market today. Both crystalline cells have similar
performances; they have high durability and a high expected lifetime of about
25 years. Of the two types of crystalline solar cells, the mono-crystalline
cells tend to be a bit smaller in size per gained watt but also a bit more
expensive than the polycrystalline cells. Single-crystalline solar cells are
cut from pieces of unbroken silicon crystals. The crystals are shaped as
cylinders and sliced into circular disks of about 1mm. An advantageous property
of the single silicon crystal cell is that they are not known to ever wear out.

Polycrystalline cells: are also ordinarily made from silicon.  However, the manufacturing process is somewhat
different. Instead for the material to be grown into a single crystal it is
melted and poured into a mould. The mould forms a squared shape and the block
is then cut into thin slices. Since the discs are squared already less or no
material has to be cut off and go to waste. When the material cools down it
crystallizes in an imperfect manner which gives the polycrystalline cells a
somewhat lower energy conversion efficiency compared to the single crystalline
cells. In consequence the polycrystalline cells are slightly larger in size per
gained watt than the single crystal cells are. After the disks of crystalline
cells (mono and poly) have been made, they are carefully polished and treated
to repair any damage the slicing might have caused.

Thin Films: A more recently developed concept is the
thin film solar cell. In principle it is a microscopically thin piece of
amorphous (non-crystalline) silicon, as an alternative to the millimeter-thick
disk, which leads to less used material. Instead of the cell being a component
in itself, the thin film cells are placed directly on a sheet of glass or
metal. Therefore, the cutting and slicing steps of the production process are
removed completely. Furthermore, instead of mechanically assembling the cells
next to each other they are simply deposited as such on the material sheet.
Silicon is the material most for the thin film cells but some other materials
such as cadmium telluride may be used. Because the cells are so thin, the
panels can be made very flexible entirely dependent on how the flexible the
material is that the cells are placed onto.

Advantages can be
won from thin film modules compared to the traditional crystalline ones in both
flexibility and weight. They are also known to perform better in poor light
conditions. However, thin film technology offers lower efficiency which means that
for the same amount of output energy a larger area would be needed. Despite the
thin films lower efficiencies, the price per unit of capacity is lower than for
crystalline sells. They also tend to degrade over time because of instability
in the material structure, making the durability of the panels less certain.

From cells to modules Solar cells are built into modules or
panels because the output from a single cell is small while the combination of
many cells can provide a useful amount of energy. Design of solar panels is
reliant of the type of solar cell that is used. The crystalline cells build
stiff modules that can be integrated between some layers of material-sheets and
then cut in different shapes whereas thin film panels are very flexible, making
them applicable in other areas. Often solar panels are located on rooftops or in separate constructions where the optimal solar angle is
received. To make sure the cell loose as little light as possible in
reflection, the incident angle is kept at a minimum. The best alternative for
the panels would be perpendicular to the incoming sunlight; which is made
complicated by the earth moving. Sometimes construction alternatives on roofs
are not available or simply undesirable due to glass roofs, flat roofs, small
gardens etc. In such cases a more flexible alternative of solar panels is found
from the ones made of thin film cell modules.





                            FABRICATION TECHNIQUES


Physical Vapor
Deposition: PVD comprises of Evaporation and Sputtering

Evaporation: Used to deposit thin layers (thin films) of
metal on a substrate. Some metals films that are easily deposited by
evaporation: aluminum, chrome gold, silver, and titanium.

Electron Beam Evaporation
(commonly referred to as E-beam Evaporation)
is a process in which a target material is bombarded with an electron beam
given off by a tungsten filament under high vacuum. The electron beam causes
atoms from the source material to evaporate into the gaseous phase. These atoms
then precipitate into solid form, coating everything in the vacuum chamber
(within line of sight) with a thin layer of the anode material. A clear
advantage of this process is it permits direct transfer of energy to source
during heating and very efficient in depositing pure evaporated material to
substrate. Also, deposition rate in this process can be as low as 1 nm per
minute to as high as few micrometers per minute. The efficiency of the material
is high in respect to different techniques and it offers the procedures of structural
and morphological control of the thin films. Because of the very high
deposition rate, this procedure has potential industrial applications for
thermal barrier coatings and wears resistant in the aerospace industries, hard
coatings for cutting and tool industries, and electronic and optical films for
semiconductor manufacturing factories.

SPUTTERING: Sputtering procedure includes ejecting material from
an “objective” that is a source onto a “substrate” (for example, a silicon
wafer) in a vacuum chamber. This impact is caused by the bombardment of the objective
by the ionization of gases which often known as an inert gas for example, argon.
Sputtering is extensively utilized in the semiconductor devices for the
deposition of thin films of various materials in the integrated circuits. The Anti-reflection
coating is additionally added by sputtering on the glass for optical
applications. Due to the low substrate temperatures utilized, sputtering is a
perfect strategy to store metals for thin-film transistors. Maybe the most
commonplace results of sputtering are low-emissivity coatings on glass,
utilized as a part of double-pane window assemblies. The most important advantage
of sputtering is that if the materials with very high melting points are very easily
sputtered while evaporating these materials in a Knudsen cell or resistance
evaporator is very problematic and complexity


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