description on the use of wonder material in solar panels to increase the efficiency of solar power generation

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A TECHNICAL SEMINAR REPORT ON
GRAPHENE USE IN SOLAR PANELS
Submitted by
SIGIRI NAVYASRI -15JJ1A0250
DEPARTMENT OF ELECTRICAL AND ELECTRONICS
ENGINEERING
Jawaharlal Nehru Technological University Hyderabad
College Of Engineering Jagtial
Nachupally (Kondagattu), Jagtial Dist - 505 501,T.S.

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JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
COLLEGE OF ENGINEERING JAGTIAL
Nachupally (Kondagattu), Jagtial Dist – 505 501,T.S.
DEPARTMENT OF ELECTRICAL AND ELECTRONICS
ENGINEERING
CERTIFICATE
This is to certify that the technical seminar report entitled “GRAPHENE USE IN
SOLAR PANELS” is a bona-fide work carried out by SIGIRI NAVYASRI – 15JJ1A0250 , in
partial fulfilment of the requirements for the degree of BACHELOR OF TECHNOLOGY
in ELECTRICAL AND ELECTRONICS ENGINEERING by the Jawaharlal Nehru
Technological University, Hyderabad during the academic year 2015-2019.The seminar
report has been approved as it satisfies the academic requirements in respect of
seminar work prescribed for the degree.
Seminar co-ordinator
Mrs. P. Sangeetha(Asst. Prof)
HOD of EEE
Mr. S. Jagadish Kumar(Asst. Prof)

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ACKNOWLEDGEMENT
I am extremely grateful to Mr.S. Jagadish Kumar, Head Of the department
Electrical and Electronics Engineering for providing me with best facilities and
encouragement.
I would like to thank my coordinator Mrs. P. Sangeetha, Assistant professor
Department of Electrical and Electronics Engineering for creative work
guidance and encouragement.

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CONTENT
s.no List of topics Page no.
1 Introduction 6
2 Graphene or graphenes 8
3 What is graphene like? 8
4 General properties 8
5 How do we make graphene 11
6 How can we use graphene 12
7 Our graphene future? 14
8 Different graphene materials 14
9 Graphene solar 18
10 Solar power advantages and disadvantages 20
11 Solar power applications 21
12 Graphene and solar panels 21
13 Novel graphene film other new concept for solar energy 22
14 Derive energy from rain drops 23
15 Graphene could double electricity generated from solar 24
16 New property revealed in graphene could lead to better
performing solar panel
27
17 Conclusion 30
18 References 31

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Abstract
If the 20th century was the age of plastics, the 21st
century seems set to become the age of graphene
A recently discovered material made from honeycomb
sheets of carbon just one atom thick. Science journals have been
running out of superlatives for this wondrous stuff: it is just about the
lightest, the strongest, the thinnest, the best heat and the electricity
conducting material ever discovered. Moreover, if we are to believe
the hype, it promises to revolutionize everything from computing to
car tires and solar cells to smoke detectors.
What! Is this strange and remarkable new stuff? Let us take
a closer look!

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Introduction
Graphene, the wonder material of the 21st century discovered amidst
theoretical studies refuting its stability in free form. Attempts to isolate and
characterize graphene began in 1800s, long before the famous discovery by Geim and
Novoselov in 2004. The discovery of graphene opened up a new world of “flatlands”
and a myriad of materials from this class is known today. This long list includes
hexagonal boron nitride, molybdenum sulphide, di-chalcogenides, single-atom layers
(phosphorene, silicene, borophene, etc.) and still counting.
What is graphene?
In school we probably learned that carbon comes in two basic but startlingly
different forms (or allotropes), namely graphite (the soft, black stuff in pencil "leads")
and diamond (the super-hard, sparkly crystals in jewellery). The amazing thing is that
both these radically different materials are made of identical carbon atoms.
So why is graphite different to diamond? The atoms inside the two materials
are arranged in different ways, and this is what gives the two allotropes their
completely different properties: graphite is black, dull, and relatively soft (soft and
hard pencils mix graphite with other materials to make darker or fainter lines);
diamond is transparent and the hardest natural material so far discovered.
If that's what we learned in school, probably finished our studies quite a while
ago, because in the last few years scientists have discovered various other carbon
allotropes with even more interesting properties.
There are
1. fullerenes (discovered in 1985; hollow cages of carbon atoms, including the
so-called Buckyball, Buckminsterfullerene, made from a kind of football-
shaped cage of 60 carbon atoms)
2. nanotubes (discovered in 1991; flat sheets of carbon atoms curled into
amazingly thin, hollow tubes one nanometer in diameter)—and (drum roll)
graphene (discovered in 2004).
crystal lattice (another name for a solid's internal, crystalline structure): lots of
atoms arranged in a regular, endlessly repeating, three-dimensional structure a bit
like an atomic climbing frame, only instead of bars there are invisible bonds between
the atoms that hold them together. Diamond and graphite both have a three-
dimensional structure, though it's completely different: in diamond, the atoms are
tightly bonded in three-dimensional tetrahedrons, whereas in graphite, atoms are
bonded tightly in two-dimensional layers, which are held to the layers above and
below by relatively weak forces.

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1) Diamond has a strong 3D (three-dimensional) crystal lattice based on a repeating tetrahedron
(left). The red blobs are the carbon atoms and the gray lines are the bonds that join them together.
(Bonds are invisible, but we draw them like this so we can visualize them more easily.)
2) Graphite has a much weaker structure based on layers of tightly bonded hexagons. The layers are
weakly joined to one another by van der Waals forces (blue dotted lines—only a few of which are
shown for clarity).
Graphene is a single layer of graphite. The remarkable thing about it is that
its crystalline structure is two-dimensional. In other words, the atoms in graphene are
laid out flat, like billiard balls on a table. Just like in graphite, each layer of graphene
is made of hexagonal "rings" of carbon (like lots of benzene rings connected together,
only with more carbon atoms replacing the hydrogen atoms around the edge), giving
a honeycomb-like appearance. Since the layers themselves are just one atom high,
you'd need a stack of about three million of these layers to make graphene 1mm thick!
Graphene has a flat crystal lattice made from interlinked hexagons of carbon atoms (red blobs) tightly
bonded together (black lines).

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Graphene or graphenes?
People talk about "graphene" the way they talk about "plastic," but it's important
to remember that scientists are working on many different kinds of graphene-based
materials (just like there are many different kinds of plastics), all of which are a little
bit different and designed to do different things. In this repot I've followed the
convention of calling the material "graphene," but it's as well to remember that this
very new, fast-evolving substance has many different angles and aspects and the word
graphene will ultimately come to refer to a very wide range of different materials.
One day, it may be common to talk about "graphenes" the way we now speak of
"plastics."
What is graphene like?
People are discovering and inventing new materials all the time, but we
seldom hear about them because they're often not that interesting. Graphene was first
discovered in 2004, but what's caused such excitement is that its properties (the way
it behaves as a material) are remarkable and exciting. Briefly, it's super-strong and
stiff, amazingly thin, almost completely transparent, extremely light, and an amazing
conductor of electricity and heat. It also has some extremely unusual electronic
properties.
 General properties
Graphene is an amazingly pure substance, thanks largely to its simple, orderly
structure based on tight, regular, atomic bonding, Carbon is a non-metal, so
you might expect graphene to be one too. In fact, it behaves much more like
a metal (though the way it conducts electricity is very different), and that's led
some scientists to describe it as a semimetal or a semiconductor (a material
mid-way between a conductor and an insulator, such as silicon and
germanium). Even so, it's as well to remember that graphene is extraordinary
and quite possibly unique.
 Strength and stiffness
If you've ever scribbled with a soft pencil (something like a 4B), you'll know
that graphite is horribly soft. That's because the carbon layers inside a stick of
graphite shave off very easily. But the atoms within those layers are very tightly
bonded so, like carbon nanotubes (and unlike graphite), graphene is super-
strong, even stronger than diamond! Graphene is believed to be the strongest
material yet discovered, some 200 times stronger than steel. Remarkably, it's
both stiff and elastic (like rubber), so you can stretch it by an amazing amount
(20-25 percent of its original length) without it breaking. That's because the
flat planes of carbon atoms in graphene can flex relatively easily without the
atoms breaking apart.

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No one knows quite what to do with graphene's super-strong properties, but
one likely possibility is mixing it with other materials (such as plastics) to
make composites that are stronger and tougher, but also thinner and lighter,
than any materials we have now. Imagine an energy-saving car with super-
strong, super-thin, super-light plastic body panels reinforced with graphene;
that's the kind of object we might envisage appearing in a future turned upside
down by this amazing material
 Thinness and lightness
Something that's only one atom thick is bound to be pretty light. Apparently,
you could cover a football field with a sheet of graphene weighing less than a
gram although it's pretty unlikely anyone has actually tried! According to my
quick calculations, that means if you could cover the entire United States with
graphene, you'd only need a mass of around 1500–2000 tons. That might
sound a lot, but it's only about as much as about 1500 cars—and
it's completely covering one of the world's biggest countries
 Heat conductivity
As if super strength and featherweight lightness aren't enough, graphene is
better at carrying heat (it has very high thermal conductivity) than any other
material—better by far than brilliant heat conductors such
as silver and copper, and much better than either graphite or diamond. Again,
we're most likely to discover the benefit of that by using graphenes in composite
materials, where we could use them to add extra heat-resistance or
conductivity to plastics or other materials.
 Electrical conductivity
This is where graphene starts to get really interesting! Materials that conduct
heat very well also conduct electricity well, because both processes transport
energy using electrons. The flat, hexagonal lattice of graphene offers relatively
little resistance to electrons, which zip through it quickly and easily, carrying
electricity better than even superb conductors such as copper and almost as
well as superconductors (unlike superconductors, which need to be cooled to
low temperatures, graphene's remarkable conductivity works even at room
temperature). Scientifically speaking, we could say that the electrons in
graphene have a longer mean free path than they have in any other material
(in other words, they can go further without crashing into things or otherwise
being interrupted, which is what causes electrical resistance). What use is this?
Imagine a strong, light, relatively inexpensive material that can conduct
electricity with greatly reduced energy losses: on a large scale, it could
revolutionize electricity production and distribution from power plants; on a
much smaller scale, it might spawn portable gadgets (such as cellphones) with
much longer battery life.

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 Electronic properties
Photos: Advances in nanotechnology, including the development of graphene, will drive faster, smaller, cheaper computers.
Picture by courtesy of Argonne National Laboratory published on Flickr under a Creative Commons Licence.
Electrical conductivity is just about "ferrying" electricity from one place to
another in a relatively crude fashion; much more interesting is manipulating
the flow of electrons that carry electricity, which is what electronics is all
about. As you might expect from its other amazing abilities, the electronic
properties of graphene are also highly unusual. First off, the electrons are faster
and much more mobile, which opens up the possibility of computer chips that
work more quickly (and with less power) than the ones we use today. Second,
the electrons move through graphene a bit like photons (wave-like particles
of light), at speeds close enough to the speed of light (about 1 million meters
per second, in fact) that they behave according to both the theories of relativity
and quantum mechanics, where simple certainties are replaced by puzzling
probabilities. That means simple bits of carbon (graphene, in other words) can
be used to test aspects of those theories on the table top, instead of by using
blisteringly expensive particle accelerators or vast, powerful space telescopes.
 Optical properties
As a general rule, the thinner something is, the more likely it is to be
transparent (or translucent), and it's easy to see why: with fewer atoms to
battle, photons are more likely to penetrate through thin objects than thick
ones. As you might expect, super-thin graphene, being only one atom thick, is
almost completely transparent; in fact, graphene transmits about 97–98
percent of light (compared to about 80–90 percent for a basic, single pane of
window glass). Bearing in mind that graphene is also an amazing conductor of
electricity, you can start to understand why people who make solar
panels, LCDs, and touchscreens are getting very excited: a material than
combines amazing transparency, superb electrical conductivity, and high
strength is a perfect starting point for applications like these.

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 Impermeability
Sheets of graphene have such closely knit carbon atoms that they can work like
super-fine atomic nets, stopping other materials from getting through. That
means graphene is useful for trapping and detecting gases but it might also
have promising applications holding gases (such as hydrogen) that leak
relatively easily from conventional containers. One of the drawbacks of using
hydrogen as a fuel (in electric cars) is the difficulty of storing it safely.
Graphenes, potentially, could help to make fuel-cell cars running on hydrogen
a more viable prospect.
On the other hand, if you pepper tiny holes into graphene to make it porous,
you get make a meshlike material called holey graphene that can work like an
electrical semiconductor or a very fine, physical sieve. Still very new, it's
already starting to find exciting applications in new forms of energy storage
(such as supercapacitors) and water filters that could reduce pressure on the
planet by helping us turn ocean water into safe, clean drinking water.
How do we make graphene?
Photo: Vapor deposition is used to create a layer of graphene on another surface (known as a substrate). Picture by Warren
Gretz courtesy of US Department of Energy/National Renewable Energy Laboratory (DOE/NREL).
Take a pencil and some sticky tape. Stick the tape to the graphite, peel it away, and
you'll get a layer of graphite made up of multiple layers of carbon atoms. Repeat the
process very carefully, over and over again, and you'll (hopefully) end up with carbon
so thin that it'll contain just one layer of atoms. That's your graphene! This rather
crude method goes by the technical name of mechanical exfoliation. An alternative
method involves loading up a super-precise atomic force microscope with a piece of
graphite and then rubbing it very precisely on something so that single layers of
graphene flake off, a bit like graphite from a pencil lead only one layer at a time.

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Techniques like this are fiddly and intricate and explain why graphene is currently
the most expensive material on the planet
These methods are fine for making tiny test samples of graphene in a laboratory, but
there's no way we could make graphene like this on the kind of industrial scale on
which it's likely to be required.
So how do you make lots of graphene? One approach is to put an organic (carbon-
based) gas such as methane into a closed container with something like a piece of
copper in the bottom, then monkey with the temperature and pressure until a layer
of graphene is formed on it. Because the graphene is formed by depositing layers of a
chemical from a gas (vapor), this method is called chemical vapor deposition (CVD).
Another approach involves growing crystals of graphene starting from a carbon-rich
solid, such as sugar.
How can we use graphene?
We can answer that question in at least three different ways.
 First, because graphene has so many excellent properties, and because all those
properties probably aren't needed in the same material (for the same
applications), it makes sense to start talking about different types of graphene
(or even different graphenes) that are being used in different ways or being
optimized for particular purposes. So we're likely to see some graphenes being
developed for structural uses (in composites materials), some being optimized
to make the most of their extraordinary electron-carrying properties (for use
in electronic components), others where we make the most of low-resistivity
(in energy-saving power systems), and still others where excellent
transparency and electrical conductivity are the important things (in solar
cells and computer displays).
Photo: Computer memory chips like this might become smaller and faster if graphene replaces the silicon we currently use.

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 Second, we can see graphene as an exciting replacement for existing materials
that have been pushed to their physical limits. Silicon transistors (the
switching devices used as memories and "decision-making" logic
gates in computers), for example, have consistently become smaller and more
powerful over the last few decades, following a trend known as Moore's law,
but computer scientists have long expressed concerns that the same rate of
progress can't continue as we approach basic limitations imposed by the laws
of physics.
Some scientists are already imagining smaller and faster transistors in which
silicon is replaced by graphene, taking computer devices even closer to the
absolute limits of physics. In theory, we could use graphene to make ballistic
transistors that store information or switch on and off at super-high speeds by
manipulating single electrons. In much the same way, graphene could
revolutionize other areas of technology constrained by conventional materials.
For example, it could spawn lighter and stronger airplanes (by replacing
composite materials or metal alloys), cost-competitive and more efficient solar
panels (replacing silicon again), more energy-efficient power transmission
equipment (in place of superconductors), and supercapacitors with thinner
plates that can be charged in seconds and store more energy in a smaller space
than has ever previously been possible (replacing ordinary, chemical batteries
entirely).
Companies such as Samsung, Nokia, and IBM are already developing
graphene-based replacements for such things as touchscreens, transistors,
and flash memories, though the work is at a very early stage.
 Third, and most exciting of all, is the likelihood that we'll develop all kinds of
brand-new, currently unimaginable technologies that take advantage of
graphene's amazing properties. In the 20th century, plastics didn't simply
replace older materials such as metal and wood: for better or worse, they
completely changed our culture into one where disposability and convenience
overtook durability. If graphenes lead us to ultra-light, ultra-thin, strong,
transparent, optically and electrically conducting materials, who knows what
possibilities might lie ahead. How about super-lightweight clothes made of
graphenes, wired to batteries, that change color at the flick of a switch? Or an
emergency house built for disaster areas, with graphene walls so strong and
light that you can fold it up and carry it in a backpack?

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Our graphene future?
Is it full-steam ahead to a future where graphene rules the world?
Maybe or maybe not. It's important not to get carried away with the hype: most of the
exciting work on graphene has so far been done on a very small scale in chemical and
physics laboratories. Most of the research is still what we'd describe as "blue sky": it
could be many years or even decades before it can be developed practically, let along
cost-effectively. By the same token, it's still very early days for basic scientific research
into graphene. Forgetting all the amazing applications for a moment, there's doubtless
much more exciting science to emerge. For example, we don't yet know if graphene
is the only material with a two-dimensional crystal lattice—or if similar but even more
extraordinary materials are just waiting to be discovered. One thing we do know is
that this is a very exciting time for materials science
Different Graphene Materials
Mentions of graphene often refer to a graphene sheet—a single layer of carbon atoms
in a perfect honeycomb lattice. The term graphene, however, is used to describe an
entire family of materials that are different in structure and properties.
Monolayer graphene sheets, often made by vacuum processes like CVD
(depositing gaseous reactants onto a substrate), are considered to be high-
quality materials with electronic properties that are potentially valuable in a
number of applications – like energy storage and generation, solar cells, and
more. However, since the process is wasteful and requires expensive
machinery, such materials are still expensive and are mainly used in research
activities - although commercial applications are slowly appearing.
Bilayer graphene (Stacking two sheets of graphene one on top of the other). It
turns out that this material differs from monolayer graphene in its electrical
properties. Just like graphene, it has a zero bandgap, but a controllable
bandgap can be introduced by applying an electric displacement field to the
two layers. A bandgap can also be introduced by stacking the two layers in a
specific arrangement. These materials are also mainly used today in various
research activities.
Few-layer graphene (FLG) (Three or more sheets of graphene can be used to
create materials - and these are referred to collectively ).
When you reach about thirty layers, the properties start to resemble graphite. The
terms graphene, FLG, bi-layer graphene and graphite are not clearly defined in a
standardized manner, which is one of the causes of confusion in the industry that is
nowadays being addressed in various standardisation efforts.

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Graphene Nanoribbons (GNRs)
GNRs are thin (under 50 nm) strips of graphene. These have interesting
electronic properties, which depend on the width and edge type of the material
(zigzag type or armchair type). In fact, GNRs can be metals, semiconductors,
half metals, ferromagnets and antiferromagnets—depending on the width,
shape, edge structures and chemical termination. Basically, GNRs are
semiconductors with an energy gap that scales (inversely) with the width of
the ribbon.
An armchair graphene ribbon (left) and a zigzag ribbon (right).
GNRs have been the focus of intensive research due to their interesting
electronic and spintronics features. GNRs have also been used to develop
several transistor designs, DNA sequencing approaches, and more.
Producing GNRs with perfect edges (zigzag or armchair) is difficult. You can
start with a graphene sheet and cut it into the desired shape. Another possible
production method is “opening” (also called “unzipping”) carbon nanotubes
(CNTs), which are rolled up sheets of graphene. Whether these methods are
cost-effective and efficient ways to produce GNRs or CNTs is yet to be seen.
GNRs today are still mainly used in small quantities for research activities.
Graphene Flakes / NanoPlatelets (GNFs / GNPs)
Producing and handling large graphene sheets is very difficult. Making
tiny “flakes” of graphene, in powder or solution form, is much easier. These
graphene flakes (GNFs) can retain some of graphene’s mechanical, thermal and
electrical properties. It is possible to synthesise GNFs in different sizes and
shapes (but not easy, however, to maintain consistency), which changes their
properties—as different sized particles behave differently in a matrix. So, a
triangle flake will behave differently than a round one, and you can also make
them in different sizes.

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Graphene flakes in dispersion, on paper.
Some GNFs are made from single-layer graphene flakes, and some are stacked
graphene flakes (few-layer graphene flakes, in fact). GNFs can be made in
different shapes, and this gives them a degree of engineering freedom you
cannot achieve with larger graphene sheets. Graphene flakes are sometimes
marketed as graphene nanoplatelets – or GNPs. A nanoplatelet is a small round
disk-shaped particle (named after its plate-shape structure). In theory,
graphene nanoplatelets are disk-shaped graphene sheets (or stacks of sheets) -
so a GNP is a type of graphene flake. In practice, it is very difficult to create
round-shaped graphene platelets—even if they are artificially synthesised.
Virtually all GNPs are not technically disk-shaped, and should therefore be
called GNFs.
GNFs are a relatively low-cost form of graphene, and found in growing use in
various composite materials.
Graphene Oxide (GO)
Graphite is a 3D material composed of many layers of graphene. Graphite
oxide is a compound of graphite (carbon), hydrogen and oxygen. In graphite
oxide, the carbon layers (the graphene sheets) are separated by oxygen
molecules. When graphite oxide is placed in water, it is easily separated into
graphene sheets – to get graphene oxide (GO) - single sheets of carbon, oxygen
and hydrogen.
Graphene Oxide flakes.

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Graphene oxide has properties quite different from those of graphene. For
example, it is dispersible in water and other organic solvents (as well as in
different matrices), whereas graphene is not. On the other hand, in terms of
electrical conductivity, graphene oxide is much less conductive than graphene
and is often described as an electrical insulator.
Graphene oxide’s unique properties make it suitable for different applications
than graphene. It is heavily studied for uses that rely on its hydrophilic nature
and lack of electrical conductivity, like water treatment membranes, medical
applications and various composite materials. Use of graphene oxide however,
is still mostly limited to R&D activity.
Reduced Graphene Oxide
Graphene oxide sheets can be reduced (which means removing the oxygen and
hydrogen) to get regular graphene sheets (called reduced graphite oxide
sheets, referred to as r-GO).
While this is a rather easy way to produce graphene sheets, those sheets usually
contain many chemical and structural defects. The chosen process of reduction
(and there are many methods, as well as the materials used) has a great impact
on the quality of the resulting rGO, and some of these can sometimes be quite
close in properties to pristine graphene.
Besides lower prices and relative ease of production, a major advantage of rGO
is the ability to scale-up its production and make it in large quantities. High-
quality rGO basically has properties similar to CVD graphene, so it is naturally
suitable for similar applications. However, the advantages listed above (like
lower price and scalability) often make it attractive when thinking of
commercialisation, and so rGO is used heavily in development work.
Graphene Quantum Dots (GQDs)
A quantum dot (QD) is a tiny semiconductor that has electronic properties
between those of bulk semiconductors and of discrete molecules. QDs are being
studied for several applications (including transistors, solar panels, LEDs and
even quantum computing) and are recently being adopted in high-end LCD
TVs.
A graphene quantum dot. (Source: Aalto University)

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The size and shape of the quantum dot control its electronic characteristics. For
example, if you use a QD to emit light in a LED-like application, the size
determines the color (wavelength) of the light. The dot's size and bandgap are
inversely related.
Graphene quantum dots (GQDs) are ultra-small graphene flakes, usually made
by cutting GNRs into 100 nanometer-long pieces. Like GNRs, GQDs are
semiconductors and have a bandgap. As in all quantum dots, the electronic
properties are related to the size and shape of the dot.
Additional Graphene Materials
There are additional graphene intermediary materials (such as inks and
coatings) and graphene-like materials. Reviewing the different materials
makes it clear that choosing the right one for a specific project is a vital first
step, as these have different properties and behaviors. Hopefully, graphene will
continue its development and live up to its potential by being integrated into
more commercial products and projects

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Graphene Solar
What is a solar panel?
Solar panel electricity systems, also known as solar photovoltaics (PV), capture the
sun’s energy (photons) and convert it into electricity. PV cells are made from layers of
semiconducting material, and produce an electric field across the layers when
exposed to sunlight.
When light reaches the cell, some of it is absorbed into the semiconducting material
and causes electrons to break loose and flow. This flow of electrons is an electric
current, that can be drawn out and used for powering outside devices. This current,
along with the cell’s voltage (a result of built-in electric fields), define the power that
the solar cell is capable of producing. It is worth mentioning that a PV cell can produce
electricity without direct sunlight, but more sunshine equals more electricity.
A module, or panel, is a group of cells connected electrically and packaged together.
several panels can also form an array, which can provide more electricity and be used
for powering larger instruments and devices.
Different kinds of Solar cells
Solar cells are roughly divided into three categories: Monocrystalline, Polycrystalline
and Thin Film.
Most of the world’s PVs are based on a variation of silicon. The purity of the silicon,
or the more perfectly aligned silicon molecules are, affects how good it will be at
converting solar energy.

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Monocrystalline solar cells (Mono-Si, or single-crystal-Si) go through a
process of cutting cylindrical ingots to make silicon wafers, which gives the
panels their characteristic look. They have external even coloring that suggests
high-purity silicon, thus having the highest efficiency rates (typically 15-20%).
They are also space efficient (their efficiency allows them to be small) and live
longer than other kinds of solar panels. Alas, they are more expensive than
other kinds and tend to be damaged by external dirt or snow.
Polycrystalline silicon (p-Si or mc-Si) solar cells do not go through the
abovementioned process, and so are simpler and cost less than Monocrystalline
ones. Their typical efficiency is 13-16%, due to lower silicon purity. They are
also bigger and take up more space.
Thin-Film solar cells (TFSC), are made by depositing one or several thin layers
of photovoltaic material onto a substrate. Different types of TFSCs are
categorized by which photovoltaic material is deposited onto the substrate:
Amorphous silicon (a-Si), cadmium telluride (CdTe), copper indium gallium
selenide (CIS/CIGS), polymer solar panels and organic photovoltaic cells
(OPC). Thin-film modules have reached efficiencies of 7-13%. Their mass
production is simple, they can be made flexible and are potentially cheaper to
manufacture than crystalline-based solar cells. They do, however, take up a lot
of space (hampering their use in residential applications) and tend to degrade
faster than crystalline solar panels.
Solar power advantages and disadvantages
Solar power is free and infinite, and solar energy use indeed has major advantages.
It is an eco-friendly, sustainable way of energy production. Solar energy systems
today are also much cheaper than they were 20 years ago, and save money in
electricity expenses. In addition, it is a much environmentally cleaner form of energy
production that helps reduce global warming and coal pollution. It does not waste
water like coal and nuclear power plants and is also considered to be a form of energy
that is much safer for use.
Although solar power production is widely considered to be a positive thing, some
downsides require mentioning. The initial cost of purchasing and installing solar
panels can be substantial, despite widespread government subsidy programs and tax
initiatives. Sun exposure is critical and so location plays a significant role in the
generation of electricity. Areas that are cloudy or foggy for long periods of time will
produce much less electricity. Other commonly argues disadvantages regard
insufficiency of produced electricity and reliability issues.

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Solar power applications
Common solar energy applications include various residential uses such as solar
lighting, heating and ventilation systems. Many small appliances utilize solar energy
for operation, like calculators, scales, toys and more. Agriculture and horticulture also
employ solar energy for the operation of different aids like water pumps and crop
drying machines. The field of transportation has been interested in solar powered
vehicles for many years, including cars, planes and boats that are vigorously
researched and developed. Solar energy also has various industrial applications,
ranging from powering remote locations as well as space and satellite systems, to
powering transportation signals, lighthouses, offshore navigation systems and many
more.
Solar technologies are vigorously researched, aiming to lower costs and improve
existing products as well as integrate PV systems in innovative products like PV-
powered curtains, clothes and laptop cases.
Graphene and solar panels
Graphene is made of a single layer of carbon atoms that are bonded together in a
repeating pattern of hexagons. It is a 2 dimensional material with amazing
characteristics, which grant it the title “wonder material”. It is extremely strong and
almost entirely transparent and also astonishingly conductive and flexible. Graphene
is made of carbon, which is abundant, and can be a relatively inexpensive material.
Graphene has a seemingly endless potential for improving existing products as well
as inspiring new ones.
Solar cells require materials that are conductive and allow light to get through, thus
benefiting from graphene's superb conductivity and transparency. Graphene is indeed
a great conductor, but it is not very good at collecting the electrical current produced
inside the solar cell. Hence, researchers are looking for appropriate ways to modify

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graphene for this purpose. Graphene Oxide (GO), for example, is less conductive but
more transparent and a better charge collector which can be useful for solar panels.
The conductive Indium Tin Oxide (ITO) is used with a non-conductive glass layer as
the transparent electrodes in most organic solar panels to achieve these goals, but ITO
is rare, brittle and makes solar panels expensive. Many researches focus on graphene
as a replacement for ITO in transparent electrodes of OPVs. Others search for ways of
utilizing graphene in improving overall performance of photovoltaic devices, mainly
OPVs, as well as in electrodes, active layers, interfacial layers and electron acceptors.
Commercialization efforts
Novel graphene film offers new concept for solar energy
Researchers at Swinburne, the University of Sydney and Australian National
University have collaborated to develop a solar absorbing, ultra-thin graphene-based
film with unique properties that has great potential for use in solar thermal energy
harvesting.
The 90 nanometre material is said to be a 1000 times finer than a human hair and is
able to rapidly heat up to 160°C under natural sunlight in an open environment.
The team stated that this new graphene-based material may also open new avenues
in:
thermophotovoltaics (the direct conversion of heat to electricity)
solar seawater desalination
infrared light source and heater
optical components: modulators and interconnects for communication devices
photodetectors
colorful display

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It could possibly lead to the development of ‘invisible cloaking technology’ through
developing large-scale thin films enclosing the objects to be ‘hidden’.
The researchers have developed a 2.5cm x 5cm working prototype to demonstrate the
photo-thermal performance of the graphene-based metamaterial absorber. They have
also proposed a scalable manufacturing strategy to fabricate the proposed graphene-
based absorber at low cost.
The reduced graphene oxide layer and grating structures were coated with a solution
and fabricated by a laser nanofabrication method respectively, which are both
scalable and low cost.
“Our cost-effective and scalable graphene absorber is promising for integrated, large-
scale applications that require polarisation-independent, angle insensitive and broad
bandwidth absorption, such as energy-harvesting, thermal emitters, optical
interconnects, photodetectors and optical modulators, Fabrication on a flexible
substrate and the robustness stemming from graphene make it suitable for industrial
use. The physical effect causing this outstanding absorption in such a thin layer is
quite general and thereby opens up a lot of exciting applications
Derive energy from raindrops
Solar panels today work best during periods of strong sunlight, but start to wane when
it gets cloudy or rainy. A breakthrough in graphene-based solar panels could change
all that, by allowing solar panels to generate electricity during inclement weather.
Graphene-based solar cells, say the researchers from the Ocean University of China,
would be able to derive energy from raindrops that happen to fall on the panel, by
taking advantage of the various salts present within the liquid.
The graphene sheets that make up the solar cells would be able to separate the
positively charged ions in rainwater, including sodium, calcium and ammonium.
These positive ions bind to the ultra-thin layer of graphene to form a double layer
(also called a pseudocapacitor) with the electrons already present. The potential
energy difference between the two layers is what generates the electrical current.
The researchers have tested a prototype by using slightly salty water to simulate rain,
and a thin-film photovoltaic cell called a dye-sensitised solar cell.
The researchers modified the cell by adding a layer of graphene, then mounting it on
a transparent backing of indium tin oxide and plastic. This dual-function solar cell
concept could then be used to produce power from both sunshine and the simulated
rainwater.

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Graphene as a material is both strong and light, and can hold energy better than
graphite. It is also being developed into anti-reflection coatings for solar cells, so the
integration of graphene into solar applications is not unheard of.
By extending the role of graphene to actively harvest energy from rainwater, the
researchers were able to generate hundreds of microvolts from the water, and achieve
a 6.53 percent solar-to-electricity conversion efficiency from the solar panel.
While these results are impressive for a conceptual prototype, there’s more work to
be done in order to raise efficiency to commercially-viable levels. One particular
problem is the relatively low concentrations of ions in raindrops, which make it a
challenge to generate enough electricity. The researchers are also working to adjust
the technology so it can handle a variety of different types of rainwater with different
ion mixtures.
However, the researchers hope their findings can guide the design of future solar cells,
and open up thinking about alternative electricity generating capabilities for solar
cells. For example, it may be possible to create solar cells that are able to harvest
energy from ambient heat and light, to boost their performance indoors.
The wider use of solar panels, such as integrating them into roofs, walls and windows
of buildings, as well as the movement to provide decentralised storage of power
generated by solar panels via battery systems.
Graphene Could Double Electricity Generated From Solar
The amount of sunlight that hits the Earth every 40 minutes is enough to meet global
energy demands for an entire year. The trick, of course, is harnessing it and converting
it into useful electricity. A new study has revealed that tweaking graphene allows it to
generate two electrons for every photon of light it receives. This could double the
amount of electricity currently converted in photovoltaic devices.
Graphene is a monolayer of carbon atoms arranged in a honeycomb pattern. It is
incredibly light, flexible, exponentially stronger than steel, and capable of conducting
electricity even better than copper. In order to make it useful in photovoltaic devices,
the researchers needed to have a better idea of graphene’s mechanism for converting
light into electricity. This process takes only a femto-second (10-15 sec), which is too
quick to easily study.
To learn more about how this energy conversion takes place, the graphene was
subjected to a treatment called “ultrafast time- and angle-resolved photoemission
spectroscopy” (trARPES).

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The material was placed in an ultra-high vacuum chamber and blasted with ultrafast
laser light, which excited the electrons and made them more capable of carrying an
electrical current. A second laser emitted pulses of light, recording the current energy
level of each electron in each pulse. These images were then put together, kind of like
a flip book, to portray the action that happens on such a short timescale.
The researchers facilitated the conversion process by ‘doping’ the graphene. That is,
they improved the material’s photovoltaic prowess by chemically altering the number
of electrons, thereby exciting them. When a photon comes and knocks an electron
back to the ground state, that one electron is able to excite two more, generating the
electric current.
“This indicates that a photovoltaic device using doped graphene could show
significant efficiency in converting light to electricity”
Doped graphene appears to be a great material to easily release the electrons and use
extra energy to excite other electrons, rather than waste the energy as heat.
Unfortunately, the material needs a little help in absorbing light; a key requirement
for photovoltaic devices. Graphene will need to be combined with other ultra-thin
materials, such as tungsten diselenide or molybednium disulphide, like has been
attempted in previous studies. This could possibly be the key in bumping solar energy
conversion from its assumed plateau of 32% up to an astonishing 60%; an increase
that could revolutionize solar energy. Moving forward, the researchers are planning
to use similar measures to investigate the photovoltaic properties of other ultra-thin
materials, including molybednium disulphide.

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By connecting a graphene layer with atomic layers of molybdenum diselenide and
tungsten disulfide, researchers were able to boost the material's carrier lifetime.
Researchers have discovered a method to increase the carrier lifetime of graphene, a
development which says could ultimately lead to the development of ultrathin, flexible
solar cells using graphene.
Graphene can transport a charge much faster than most other materials, which would
make it an excellent solar cell material. However, it is held back by its extremely short
carrier lifetime, which means that electrons excited by sunlight only remain mobile
for one picosecond (one millionth of a millionth of a second).
To overcome this problem, the researchers looked at methods to suppress
recombination of the electrons, and keep them mobile for long enough to create a
charge.
The method used, Unipolar optical doping and extended photocarrier lifetime in
graphene by band alignment engineering, published in the journal Nano Futures,
connects a graphene layer with two other atomic material layers – molybdenum
diselenide (MoSe2) and tungsten disulfide (WS2).
Combining the materials in this way, the researchers were able to increase the carrier
lifetime of the material from 1 to around 400 picoseconds. Their experiment used a
0.1 picosecond laser pulse to ‘excite’ some electrons in the molybdenum disulfide
layer, and monitoring them using a second laser pulse.
“We can think of the MoSe2 and graphene layers as two classrooms full of students
all sitting, while the middle WS2 layer acts as a hallway separating the two rooms,”
he explains.
“When light strikes the sample, some of the electrons in MoSe2 are liberated. They
are allowed to go across the WS2-layer hallway to enter the other room, which is
graphene.
However, the hallway is carefully designed so that the electrons have to leave their
seats in MoSe2. Once in graphene, they have no choice but to stay mobile and hence
contribute to electric currents, because their seats are no longer available to them.”
The researchers now plan to experiment with different material layers in combination
with graphene, to gain better control over the lifetime of the excited electrons.
Researchers recently made a discovery using MoSe2 and similar compounds, known
as van der Waals materials, and is continuing research to gain better control over
electron excitation.

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New property revealed in graphene could lead to better performing solar
panels
Shining light on graphene: Although graphene has been studied vigorously for more
than a decade, new measurements on high-performance graphene devices have
revealed yet another unusual property. In ultra-clean graphene sheets, energy can
flow over great distances, giving rise to an unprecedented response to light.
Discovered a new mechanism for ultra-efficient charge and energy flow in graphene,
opening up opportunities for developing new types of light-harvesting devices.
The researchers fabricated pristine graphene- graphene with no impurities into
different geometric shapes, connecting narrow ribbons and crosses to wide open
rectangular regions. They found that when light illuminated constricted areas, such
as the region where a narrow ribbon connected two wide regions, they detected a
large light-induced current, or photocurrent.
The finding that pristine graphene can very efficiently convert light into electricity
could lead to the development of efficient and ultrafast photodetectors and potentially
more efficient solar panels.
Graphene, a 1-atom thick sheet of carbon atoms arranged in a hexagonal lattice, has
many desirable material properties, such as high current-carrying capacity and
thermal conductivity. In principle, graphene can absorb light at any frequency,
making it ideal material for infrared and other types of photodetection, with wide
applications in bio-sensing, imaging, and night vision.
In most solar energy harvesting devices, a photocurrent arises only in the presence of
a junction between two dissimilar materials, such as "p-n" junctions, the boundary
between two types of semiconductor materials. The electrical current is generated in
the junction region and moves through the distinct regions of the two materials.

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"But in graphene, everything changes," said Nathaniel Gabor, an associate professor
of physics at UCR, who co-led the research project. "We found that photocurrents
may arise in pristine graphene under a special condition in which the entire sheet of
graphene is completely free of excess electronic charge. Generating the photocurrent
requires no special junctions and can instead be controlled, surprisingly, by simply
cutting and shaping the graphene sheet into unusual configurations, from ladder-like
linear arrays of contacts, to narrowly constricted rectangles, to tapered and terraced
edges."
Pristine graphene is completely charge neutral, meaning there is no excess electronic
charge in the material. When wired into a device, however, an electronic charge can
be introduced by applying a voltage to a nearby metal. This voltage can induce positive
charge, negative charge, or perfectly balance negative and positive charges so the
graphene sheet is perfectly charge neutral.
"The light-harvesting device we fabricated is only as thick as a single atom," Gabor
said. "We could use it to engineer devices that are semi-transparent. These could be
embedded in unusual environments, such as windows, or they could be combined
with other more conventional light-harvesting devices to harvest excess energy that
is usually not absorbed. Depending on how the edges are cut to shape, the device can
give extraordinarily different signals."
The research team reports this first observation of an entirely new physical
mechanism a photocurrent generated in charge-neutral graphene with no need for
p-n junctions in Nature Nanotechnology today.
Previous work by the Gabor lab showed a photocurrent in graphene results from
highly excited "hot" charge carriers.
When light hits graphene, high-energy electrons relax to form a population of many
relatively cooler electrons, Gabor explained, which are subsequently collected as
current. Even though graphene is not a semiconductor, this light-induced hot electron
population can be used to generate very large currents.
"All of this behavior is due to graphene's unique electronic structure," he said. "In this
'wonder material,' light energy is efficiently converted into electronic energy, which
can subsequently be transported within the material over remarkably long distances."
He explained that, about a decade ago, pristine graphene was predicted to exhibit very
unusual electronic behavior: electrons should behave like a liquid, allowing energy to
be transferred through the electronic medium rather than by moving charges around
physically.
"But despite this prediction, no photocurrent measurements had been done on pristine
graphene devices until now," he said.

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The new work on pristine graphene shows electronic energy travels great distances
in the absence of excess electronic charge.
The research team has found evidence that the new mechanism results in a greatly
enhanced photoresponse in the infrared regime with an ultrafast operation speed.
"We plan to further study this effect in a broad range of infrared and other
frequencies, and measure its response speed”.

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CONCLUSION
Solar power is looking more and more attractive, as other power generation
methods such as fossil fuels and nuclear power come under increasing scrutiny
Nano material solar cells shows special promise to both enhance efficiency of
solar energy conservation and also reduce the manufacturing cost
It increase efficiently by the absorption of light as well as the overall radiation
to electricity would help preserve the environment, decrease wastage, provide
electricity for rural areas, and have a wide array of commercial applications
due to its capabilities

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References
https://onlinelibrary.wiley.com/doi/abs/10.1002/aenm.201100119
https://www.azonano.com/article.aspx?ArticleID=4565
http://www.iosrjournals.org/iosr-jmce/papers/vol11-issue6/Version-
2/J011627181.pdf
http://news.mit.edu/2017/mit-researchers-develop-graphene-based-
transparent-flexible-solar-cells-0728
https://www.sciencedirect.com/science/article/pii/S2211285518301150