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

1. GRAPHENE
A TECHNICAL SEMINAR ON
By – SIGIRI NAVYASRI
(15JJ1A0250)
JNTUH COLLEGE OF ENGINEERING JAGITAL
Nachupally, kondagattu – jagital 505501

2. CONTENTS
• Introduction
• History
• Structure
• Properties
• Other forms of graphene
• Application
• Solar photocells mechanism
• Solar application of graphene
• Challenges to unlock
• Advantages
• Limitations
• Conclusion
• References

3. INTRODUCTION
• Graphene = graphite + ene
• In 1987, Graphene used for single sheets of graphite.
What is graphene?
• Graphene can be described as a one atom thick layer of graphite.
• It is the basic structural element of other allotropes, including graphite, charcoal, carbon nanotubes and
fullerenes.
• Graphene is the strongest, the thinnest, material known to exist.

4. HISTORY
• One of the very first patents pertaining to the production of graphene was filed on October, 2002 entitled, “Nano-
scaled Graphene plates”.
• Two years later, in 2004 Andre Geim and Kostya Novoselov at University of Manchester extracted single-atom-
thick crystallites from bulk graphite.
• Geim and Novoselov received several awards for their pioneering research on graphene, notably the 2010 Nobel
Prize in Physics.

5. STRUCTURE
• Graphene is a 2 – dimensional network of carbon atoms
• These carbon atoms are bound within the plane by strong bonds into a honeycomb array comprised of six – membered
rings
• By stacking of these layers on top of each other, the well known 3 – dimensional graphite crystal is formed
• It is a basic building block for graphitic materials of all other dimensionalities
• It can be wrapped up into 0D fullerenes, rolled into 1D nanotubes or stacked into 3D graphite

7. PROPERTIES OF GRAPHENE.
• STRUCTURAL
a. Graphene can self-repair holes in its sheets, when exposed to molecules containing carbon, such as
hydrocarbons.
b. Bombarded with pure carbon atoms, the atoms perfectly align into hexagons, completely filling the
holes.

8. • CHEMICAL
a. Graphene one atom thick are a hundred times more chemically reactive than thicker sheets. (Stanford university)
b. Graphene is chemically the most reactive form of carbon.
• ELECTRONIC
a. Intrinsic graphene is a semi-metal or zero-gap semiconductor.
• ELECTRICAL
a. Graphene has a remarkably high electron mobility at room temperature, with reported values in excess of 15000 cm2·V−1·s−1
b. It conducts electricity as efficiently as copper and outperforms all other materials as a conductor of heat.

9. • THERMAL
a. A graphene sheet is thermodynamically most stable
a. only for molecules larger than 24,000 atoms
b. Size greater than 20 nm
b. Thermal conductivity is measured to be between (4.84±0.44) × 103 to (5.30±0.48) × 103 W·m−1·K−1
• MECHANICAL
a. The flat graphene sheet is unstable with respect to scrolling , i.e. bending into a cylindrical shape
b. As of 2009, graphene appeared to be one of the strongest materials known with a breaking strength over 200 times greater than a
hypothetical steel film of the same thickness, with a young’s modulus(stiffness) of 1 TPa (150000000psi).
c. 1 square meter graphene hammock would support a 4 kg cat but would weigh only as much as one of the cat's whiskers, at 0.77 mg
(about 0.001% of the weight of 1 m2 of paper)

10. • OPTICAL
a. one-atom-thick crystal can be seen with the naked eye because it absorbs approximately 2.3% of white light
b. Graphene's unique optical properties produce an unexpectedly high opacity for an atomic monolayer in vacuum
FIG; 4 inch scale graphene film on Stretchable Substrate

11. OTHER FORMS OF GRAPHENE
• Nanostripes- application in new field of spintronics
• Graphene oxide (go)- used in water remediation and reactive gas
Adsorption (environmental application)
• Soluble fragments of graphene- (through chemical modification)
• 3D GRAPHENE (self-supporting 3D graphene has not yet been produced)
• BILAYER GRAPHENE - bilayer graphene typically can be found either in twisted configurations where the two layers
are rotated relative to each other.

12. SOME PRODUCTION METHODS
• MECHANICAL EXFOLIATION :
This involves splitting single layers of graphene from multi-layered graphite. Achieving single layers typically requires multiple
exfoliation steps, each producing a slice with fewer layers, until only one remains. Geim and Novosolev used adhesive tape to split
the layers.

13. • EPITAXY :
Epitaxy refers to the deposition of a crystalline overlayer on a crystalline substrate and the graphene–substrate interaction
can be further passivated
In some cases epitaxial graphene layers are coupled to surfaces weakly enough (by Van der Waals forces)
Sicilicon-based epitaxy technology for producing large pieces of graphene with the best quality to date
EPITAXY EXAMPLES :
Silicon carbide
Metal substrates
Copper Vapor Deposition ( CVD)

14. • Reduction of graphite oxide
• Metal carbon melt
• Solvent exfoliation
• Carbon dioxide reduction
• Nanotube slicing

15. APPLICATIONS
• Filters
a. desalination - by very precise control over the size of the holes filters could outperform other
techniques of desalination by a significant margin
b. ethanol distillation – graphene oxide membranes allow water vapour to pass through, but are
impermeable to other liquids and gases
c. such membranes could revolutionize the economics of biofuel production and the alcoholic beverage
industry

16. • Energy storage devices – due to the extremely high surface area to mass ratio of graphene, it is believed
that it could be used to produce supercapacitors with a greater energy storage density than is current
available
• Ultra capacitors:
a. Due to incredibly high surface-area-to-mass ratio of graphene, its one potential application is in the
conductive plates of ultra capacitors.
b. Graphene could be used to produce ultra capacitors with a greater energy storage density than is currently
available.

17. • Solar cells – promising material for photoelectrochemical energy conversion in dye sensitized solar cells, exhibits
a high conductivity of 550 s/cm and a transparency of more than 70% over 1000 – 3000 nm
• Integrated Circuit
a. Graphene has the ideal properties to become an excellent component of integrated circuits.
b. Its high carrier mobility & low noise allow it to be used as a channel in FETs.
c. Besides, the researchers have demonstrated the first functional graphene integrated circuit-a complementary inverter
consisting of one p- & one ntype graphene transistor.

18. • Anti-Bacterial:
a. Sheets of graphene oxide are highly effective at killing bacteria's such as Escherichia coli.
b. So, graphene could be useful in hygiene products or packaging.
• Strength Applications:
a. When graphene sheets are incorporated into composites, we could come up with a material that’s many
times stronger than Kevlar.
b. The Chinese are already working on carbon- nanotube yarn for space suits & bullet proof vests.

19. • T-Ray Scanners:
a. Terahertz radiation, or T-ray is used for detecting hidden objects at security checkpoints without the health risk posed
by X-rays.
b. The fast frequencies generated by graphene circuits are the basis for chemical sensors & generators of THz-range
light.
• Heat Dissipation to cool electronics:
a. Overheating in laptops & other electronic gadgets is a major technological hurdle to the speed & energy efficiency of
electronic products.
b. Graphene behaves as a strong heat conductor, which helps chip manufacturers to rich higher speeds with relative
lower temperatures.

21. SOLAR PHOTO CELLS MECHANISM
how does solar panel work?
• Solar photocells catch sunlight that fall into the PN junction. Through the photoelectric effect, electrons that
absorb photons will jump across the energy gap barrier, from the valence to the conduction band, and flow out
around the circuit, generating electricity. The more light that shines, the more electrons jump up and the more
current flows. So, the Current depends on illumination and area but the Voltage depends on built-in field
between the P side and the N side.
• Virtually all of today’s solar cells are made from slices of silicon

23. GRAPHENE SOLAR PANELS
• 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 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.
• 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).

24. • 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.

25. GRAPHENE COULD LEAD TO BETTER PERFORMING SOLAR PANELS
• 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.

26. • With its super conductivity, graphene could play a huge part in the future of solar power.
• And in revolutionizing electric cars by enhancing their batteries – making them more efficient and eventually more
affordable

27. CHALLENGES TO UNLOCK
• Cost reduction
• Handling
• Growth on wafer scale
• Challenges in making stronger composite material
• Application in aircraft parts
• Low cost- high sensitivity sensors
• Application in electrical energy storage

28. ADVANTAGES
• Higher electron mobility
• Works on principle of diffraction of electrons.
• Superb electron & heat conductivity, greater than copper.
• Very less breakover voltage, less than 0.3V
• It is transparent, yet so dense as even an atom of Helium can’t pass through it.
• Stronger than diamond & steel
• Can be used to make anti bacterial materials as well as biodevices.
• Can make very light weight parts for auto bodies & armours

29. LIMITATIONS
• Single sheet of graphene is hard to produce.
• The new fabrication & manufacturing methods has to be evolved for normal use in electronics.
• Due to small voltage gain, practical use is limited.
• While graphene can be considered semiconductor like silicon, it lacks one crucial property- the ability to act as a
switch.
• Graphene research has discovered hidden interactions that will affect the way components are designed from the
superfast material.

30. 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