Hello my friends, today we are going to discuss
about our 2nd chapter on Solar Energy Harvesting.
So, before going to start just let us know
the what is solar energy.
So, basically like water and air, the sun
is one of the earth’s life support systems
providing the heat and light as we know; because
if there is no sun then our life maybe will
become miserable or maybe after certain time
we cannot sustain on this earth.
So, solar energy basically is the form of
energy relies on the nuclear fusion power
from the core of the sun.
So; that means, actually the solar energy
we are getting from the sunlight itself.
An hour of solar radiation on earth provides
the 14 terawatt years of energy almost the
same as the world’s total annual energy
consumption.
So, from this particular statement you can
understand that how much energy basically
we are getting from the sun.
Solar energy is a free inexhaustible source,
yet harnessing it is relatively new idea.
Harnessing means just capturing the solar
energy and from capturing the solar energy
just convert it into some other energy so
that we can utilize this solar energy.
Because, as we know that when the suns comes;
it is comes to our whole earth surface.
So, some portions basically we are using,
but some we are wasting also.
If we able to capture that particular energy
and if we are able to convert that particular
energy into some energy.
So, of course, that is come on to the renewable
energy without less cost maybe we can produce
some kind of electricity.
And, also it is a very good for the near future
because when our fossil fuels are really going
down.
So, why solar energy?
In the whole world coal deposits will deplete
within next 200 to 300 years and petroleum
deposits will deplete in next few decades
at the present rate of consumption.
So, of course, because whatever the coals
we are having under the soil every day we
are extracting through mines.
So, of course, after certain time that will
be finished and whatever the petroleum we
are getting from the soil or maybe some extractions
from the fossil fuels.
So, basically that petroleum or may be the
coal is having some time that after that we
are unable to extract it or maybe it be gone
down or may be finished.
So, basically that time we have to depend
up to on maybe some other technology or maybe
other inventions from where we can generate
the electricity or maybe the thermal power
or maybe some kind of other means.
So, the huge consumption of the fossil fuels
has caused many damages to the environment.
Yes of course, because when we are cutting
down the trees of course, it is creating a
lots of problems towards the pollutions.
As we know that nowadays every year our pollution
level is increasing tremendously all over
the world.
And, then automatically when we are cutting
those trees automatically the land sliding
and maybe the season changing is quite obvious
which is affecting our day to day life.
And, not only that sometimes it may happen
that when we are cutting those trees and then
burning so, it is creating so many toxic gases
into the environment which is also one of
the causes for increase into the pollutions.
So, to reduce these damage we need to concentrate
on renewable energy sources, and solar energy
is the one which is available abundantly.
Yes of course, because we can get this kind
of energy unless and until up to the life
of the whole sun.
So, automatically if we were able to explore
this kind of energy from the solar light;
So, automatically at least for next few decades
or maybe the next few years at least we can
think that we can get the constant energy
from preserving this sunlight or may be from
this particular sun.
So, the most advantage using solar energy
is that this is distributed over a wide geographical
area because all over the world the sunlight
is coming, ensuring the developing region
such as India have access to electricity generation
at a stable cost for the long term future
whatever I have already explained.
So, now what is the importance of the solar
energy?
Why nowadays every people are talking about
the renewable energy, solar energy or maybe
the solar power systems?
Because, from this particular table we can
understand that how important it is; in this
particular case it is showing the amount of
the carbon and the Sulphur deposited in the
atmosphere.
See, if I talk about the vehicle or maybe
the waste products means like a exhaust gas
what is coming from the vehicle itself, the
amount deposit in the atmosphere is 8 billion
tons.
If we talk about the fossil fuels it is about
the 6.5 million tons.
If we talk about the deforestation and the
forest firing it is cost around 1.5 million
tons.
So now, at present so many alternative fuels
have been developed still they are able to
meet a small proportion of our actual demand.
Yes of course, because the solar energy or
maybe the sunlight is the means the quantity
what we are getting is a huge.
So, if we are able to develop certain technology
where we can absorb the maximum solar energy.
So, that will be the very good for our near
future because other this alternative fuels
or may be the fossil fuels what happened,
because they are having certain limitations.
If I having this much of quantity I can generate
this much of only the electricity, but the
solar light it is countless almost.
So, if I am able to construct certain kind
of devices all over the world so, I can capture
the whole sunlight and I can do use that particular
sunlight for generating the electricity; that
means, it is almost countless and the any
number of productions we can do it.
So, now in this particular image the data
has been taken from the CEA, MNRE that is
the Ministry of Renewable Energy, Mercom India
Solar Project Tracker.
So, they are telling that installed capacity
of the solar energy in India till today.
So, till 56.23 percentage basically we are
depending upon the coal.
If we talk about the hydro then it is 13.04
percentage, gas is 7.13 and nuclear is 1.94
percentage because the availability of the
nuclear materials is very less, if we talk
about the diesel its only 0.24 percent.
Now, you can see that if we talk about the
renewable energy it is coming almost 21.41
percent which is the second largest one just
after the coal.
So, now you can think that if in future the
coal will be finished; so, that time that
area can be taken care by the renewable energy.
So, in future maybe the renewable energy will
be the 100 percent.
So now, if we talk about the renewable energy
that is also divided into several parts so,
basically if we talk about the wind energy.
So, just simple we can use certain kind of
turbine and then wind power on with the speed
we rotate the turbine.
So, then the turbine is rotating the generator
and then it is generating the 9.93 percentage.
If we talk about the solar it is taking 7.46
percentage, if we use the bio-power or maybe
the biomaterials or maybe the biofuels so,
that time it is 2.70 percentage.
If we having the small hydro turbine plant
then we can generate up to 1.29 percentage
and of course, there is certain waste to power
that is called as 0.04 percentage.
So now, you can see that how tremendously
the solar is coming up.
So, maybe the solar energy can replace all
other non-conventional renewable energy in
later future.
Now, let us talk about the history of the
solar energy.
So, basically you can see in the year of 1839
by Edmund Becquerel he has observed that materials
which turn light into the energy.
So, basically you can see; that he has seen,
that the material which can turn light to
energy; that means, if I am having certain
materials if I put the light over there then
automatically it will generate the electricity
or maybe the energy.
So, basically he has started this one in the
year of 1839, then followed by 1860 by Auguste
Mouchout who has seen that direct conversion
of solar radiations into the mechanical power.
So, basically like this way slowly slowly
we have come down to up to 1954 when the Fuller,
Pearson and the Chaplin they discovered that
silicon as a semiconductor with efficiency
of 6 percent.
Then later in 2009 that Miyasaka who has developed
the perovskite materials into the solar cells.
So, from this particular chat you can understand
that first initially we have identified the
materials where we can put the light and it
can generate certain kind of energy.
Then slowly slowly we have come to the silicon
solar systems, then from silica solar systems
we have moved to the dye sensitized solar
systems and nowadays people are trying to
work on to the perovskite solar system.
So, basically the materials we are changing
just to achieve the more efficiency from the
solar light.
So, automatically still today the research
is going on and hopefully maybe within certain
years we can achieve near about 50 percent
of the efficiency from the solar light.
Now, what are the advantages of the solar
energy?
After the initial investment has been recovered
the energy from the sun is practically free.
Of course, because first initial stage we
have to set up the device and then that device
can works for a longer time.
So, a very less maintenance cost is required,
only the initial start up cost is little bit
higher.
Then we talk about the financial incentives
are available from the government that will
reduce your cost.
Yes of course, now in everywhere the from
the government like MNRE or maybe some other
source they are putting the solar water heater
or maybe some kind of solar panel with all
the government institutions or maybe the government
offices.
So, that at the roof whatever the solar energy,
solar light basically we are wasting.
So, by capturing those solar light and convert
to it is into the electricity.
So, at the time of our normal electricity
off, maybe we can use that particular energy
to solve the problems or maybe the to continue
our experimentations or may be running of
the machines or may be the running of the
office buildings in the night time.
Solar energy is also very clean, renewable,
sustainable and helping to protect our environment
because this is almost the pollution free.
Once installed there are no recurring costs,
they operate saliently have no moving parts.
So, only you are having the collector where
the sunlight is coming and then through that
collector it is converting into the from solar
light to the electricity.
And, then just that electricity we are storing
into some device and then at the time of requirement
just we are using that particular energy.
Of course, there are certain disadvantages
of the solar energy also; the initial cost
is the main disadvantage of installing a solar
energy systems as I told already.
So, that is why the government is giving so
many types of incentives in terms of the loans
or maybe the helping to the other peoples
for opening their own business or maybe the
startups.
So, that they can install the solar energy
and then after that slowly slowly when they
are going to get certain profit and they are
going to return it to the government or maybe
the nationalized bank.
Solar panels required quite large area for
installations to achieve a good level up efficiency.
Yes of course, because as I told already the
efficiency is too less maybe that time one
solar panel or maybe the two solar panels
will not be good enough to generate the high
amount of electricity.
So, that time you need a larger area so, that
you can put so many solar panels and you can
generate a quite reasonable amount of the
electricity at that particular time.
Now, what are the classifications of the solar
energy?
So, basically the solar energy is divided
into two parts: one is called the passive
and one is called the active.
So, if we talk about the active, active is
also divided into two parts; one is called
the solar thermal, another one is called the
photovoltaics.
And, then solar thermal is like the concentrated
solar thermal and photovoltaics is also divided
into two parts: one is called the crystalline
another one is called the thin films.
Now, we are going to discuss one by one into
the next subsequent slides.
So, what is passive solar energy?
So, basically from the name itself we can
understand that this is passive, this is not
directly active.
So, basically passive solar is a energy is
method in which solar energy is harnessed
in its direct form without using any mechanical
devices.
Say suppose you can understand in our childhood
our mother use to put one bucket of water
into the sunlight into winter time.
Why?
Because, the thing is that after getting certain
kind of sunlight that water can get little
bit warm so, that we can use it for our bath
purpose.
So, that is called the passive solar energy
because here I am not going to use any kind
of mechanical means directly I am using that
particular solar energy into our systems.
So, say suppose in the home or maybe the house
or maybe the big building we are putting certain
kind of glass opening kind of things where
the direction light it can come and heated
that particular room.
We are having the passive solar cooling also,
say suppose direct sunlight is coming and
we are passing the water through it and then
the water is getting little bit heated up
and then it is releasing certain kind of moisture.
So, that we can get it cool down, we are having
some kind of passive solar heating kind of
things, where we can use directly the sunlight
to heat inside the room.
So, anyway we are not using any kind of mechanical
device.
So, directly we are using the solar light
or maybe the sunlight into our system.
Now, when you are talking about the active
solar energy that means, as I told already
we are using certain kind of mechanisms, we
are using certain kind of machines to store
that particular solar energy so, that it can
convert into certain energy.
How?
So, the active solar energy employs mechanical
or electrical equipment for functioning and
increase system efficiency.
As an example water pumps are used to circulate
water through the active solar energy water
heating systems.
Some application of active solar energy which
can be very helpful to all of us is like this.
What are those?
First in this particular case we are having
the active solar space heating.
So, in this particular case what you are seeing?
The sunlight is coming on top of this panel
and through this we are having; the we are
passing the air through this particular channel.
So, the air is getting inside in this through
this channel and then it is coming out.
So, when air is coming through due to that
sunlight the air is heated up and then that
heat air we are using inside the room in winter
time.
So, like this way we are capturing the solar
energy.
In this particular case, also we are nowadays
we are using the active solar pool heating.
So, in the winter times we that we can use
that particular swimming pool because the
water will getting warm over there.
So, here is the another example where is the
active solar water heating systems.
So, it is also like that same instead of air
just we are circulating the water through
that particular panel; so that water is getting
heated up by the sunlight directly and then
we are using that hot warm water for our daily
purpose.
Next there are several types of active solar
energy like that solar thermal energy; so,
solar thermal power generation systems collect
and concentrate sunlight to produce the high
temperature heat needed to generate the electricity.
All solar thermal power systems have solar
energy collectors with two main components,
one is called reflectors that is nothing,
but the mirrors and that capture and focus
sunlight onto a receiver.
So, basically in most cases of system, a heat
transfer fluid is heated and circulated in
the receiver and use to produce the steam.
The steam is converted into mechanical energy
in a turbine which powers a generated to produce
electricity.
So, from this particular image we are trying
to so, that how basically we are generating
the electricity.
We are having that solar collector; we are
having the reflector field.
So, simple what is happening?
When the sunlight is coming, the sunlight
is reflecting on to the mirror.
Then I am having the receiver over there so,
just I am rotating this one.
So, that the full concentration of the sunlight
will fall upon this one and inside it we are
having that water or maybe some other means
which will be heated up.
And, then through that it will generate into
the vapor and through that vapor it will rotate
the turbine and then turbine is coupled with
the generator.
So, automatically the generator will generates
the electricity and that electricity we are
sending to our day to day life.
So, this is the basically the concept over
here for the solar thermal energy.
Next is called the photovoltaics solar cell
energy.
So, it is a one kind of battery kind of mechanism.
So, photovoltaics cell consist of two or more
thin layers of semiconducting materials most
commonly the silicon, it is widely used.
It is an electrical device that converts the
energy of light directly into the electricity
by the photovoltaic effect.
So, the effect is called the photovoltaics
so, that is why it is called the photovoltaics
solar cell energy; basically the mechanism
is known as the photovoltaics.
So, photovoltaics is derived from the words
photo, photo is the Greek meaning is having
the light and the voltaic meaning is called
the voltage.
So; that means, it is basically the light
voltage.
So, light is generating the potential difference
over here.
So, the basic operation of a semiconductor
photovoltaics cell involves two steps: one
is called the absorption of light which leads
to the generation of electron hole pairs within
the photovoltaic materials.
The separation of this electron hole pairs
giving rise to an electrical current which
flows a in an external circuit.
So, simple in this particular case you can
see that; in other words we can say that when
the electron is moving from one place to another.
So, what is happening?
Here it was the electron so now, here the
electron is going into this place.
So, automatically some vacant positions is
creating at that particular point.
So, if the electron will go automatically
the vacant will flow into the opposite directions
so, that is nothing but known as the electron
hole pairs over there.
So, that is creating the some kind of holes
when the electron is leaving one place to
another.
So, now basically the classification of solar
cell based on materials there are several
classifications.
One is called the first generations, then
second generations and the third generations.
If we talk about the first generation solar
cells; so, basically it is divided into two
parts: one is called the monocrystalline solar
cells another one is called the polycrystalline
solar cells.
If we talk about the second generations we
are having that amorphous silicon thin film
solar cells, we are having that CdTe, CIS,
CIGS thin film solar cells what are those
I will tell you in brief.
So, if you talk about the third generation
solar cells so, first is called the organic
solar cells, dye sensitized solar cells, quantum
dot solar cells, nanocrystalline based solar
cells and last one the perovskite solar cells
which you are going to discuss into our next
lecture.
So, first is called the first generation solar
cells.
So, first generation solar cells includes
single and the polycrystalline silicon materials.
Here silicon which is first melted then crystallizes
ingots or castings of pure silicon.
Thin slices are cut to form a single crystals
of silicon which is known as the mono crystalline
or to form a block of silicon crystals which
is nothing, but that polycrystalline to make
the individual cells.
So, the conversion efficiency for these cells
range from 10 to 20 percent.
So, in this particular case when you are talking
about the mono; So, basically mono case you
see to make cells for mono crystal and panel
silicon is formed into bars and cut into wafers.
And, when you are talking about the poly to
make cells from poly crystalline panels fragments
of silicon are melted together to form the
wafers.
So, in this case it is the one and poly means
many; so, so many silicon crystals basically
we are using.
So, here is a more prominent image of the
mono and the poly.
Next we are going to talk about the second
generation solar cells.
So, basically these solar cells aims to use
less material while maintaining the efficiencies
of first generation photovoltaics.
So, basically they involves the amorphous
silicon that cadmium telluride, copper indium
diselenide, copper indium gallium diselenide.
So, basically a-Si, CdTe and CIGS absorb the
solar spectrum much more efficiently than
single crystalline silicon and use only 1
to 10 micrometer thickness of active materials.
So, here from this particular line you can
understand that we need a less amount of material.
Thin film technology is less expensive since,
it uses fewer materials and less manufacturing
process.
So, if we talk about the amorphous silicon
where basically we are putting that particular
materials.
So, in this particular case you can see that
we are having that metal back contact then
top of that we are putting one interlayer;
And, in this particular case basically we
are using the amorphous silicon and then we
are having that front contact TCO and the
glass superstrate.
So, like this way basically in this particular
case we are using the CdTe absorber, in this
particular case basically you are using the
CIGS absorber.
So, from this you can understand that almost
the manufacturing process is almost same,
only basically we are changing the materials
just to increase the efficiency.
Next we are going to discuss about the amorphous
silicon thin films.
What is that?
Amorphous silicon has limited short range
order, so its physics is completely different
from that of the crystalline silicon.
With the development of nanotechnology we
can create homogeneous layer of amorphous
silicon to absorb the short wavelength photons.
Periodical amorphous silicon nanorods structures
for light trapping enhancement for longer
wavelength photons, nanocone amorphous silicon
structure to improve carrier collection efficiency.
So, basically you can see that we are having
that glass substrate on top of that we are
putting some metallic back reflector and the
contact and then we are having that N-type
silicon, I-type silicon and the P-type silicon.
And.
next we are having the transparent conductive
oxide and again we are having that glass.
So, basically the solar cell is coming.
So, in this particular case the electron is
jumping from here to here; P-type to the N-type
one.
When the electron is jumping; automatically
you can see the hole pair is creating in this
particular case.
So, now when the electron is coming hole pair;
so, automatically now the electron in other
way when it is going to that it will make
the balance.
So, that is why the current is flowing from
here to here.
Next we are having that cadmium telluride
thin film cells.
So, in short generally we are calling it as
a CdTe.
So, is a polycrystalline semiconductor material
made from cadmium and tellurium.
CdTe has a high light absorptivity level that
is only about 1 micrometer thick semiconductor
can absorb 90 percent of the solar spectrum.
Now, we can understand in our last lecture
if you see properly; so, you can see that
we are having 1 to 10 micrometer.
But, in this particular case you can see that
only we are using the 1 micrometer thick systems
and it can absorb the 90 percent of the solar
spectrum.
So, CdTe cells have been fabricated by physical
deposition, spraying, screen printing followed
by sintering and electrodepositions.
Of course, there is certain disadvantages,
what is that?
Cadmium is a toxic heavy metal can pollute
the environment if the cell is damaged or
maybe the broken; that means, if the cadmium
can come into the contact with the air; so,
that time it creates certain kind of pollutions
to the environment.
So, the same like it is the amorphous silicon,
in this case only we are replacing the amorphous
silicon by the CdTe material.
Next we are having that CIS and CIGS thin
film solar cells.
So, CIS is a polycrystalline semiconductor
material composed of C stands for Copper,
I stands for Indium and S stands for Selenium.
So, basically it is the copper indium di-selenide.
So, CIS cells are most light absorbing semiconductor
compounds, absorbing up to 90 percent of the
solar spectrum.
CIGS: Copper Indium Gallium di-selenide is
multilayer thin film composite materials.
The addition of small amounts of the compound
gallium to CIS produce a photovoltaic cell
with higher conversion efficiency.
That means, the people everyday they are researching
on it that which type of materials, if I add
into the system so, that it can increase the
efficiency of that particular systems.
So, n number of researchers are working on
nowadays on this particular solar photovoltaic
system.
So, in this particular case in this here basically
we are using the CIS or maybe the CIGS absorbing
materials.
Next come to the last one which is called
the third generation solar cells, it is also
divided into several parts.
So, basically the third generation solar cells
are solution processable solar cells with
excellent potential for large scale solar
electricity generation.
This solar cells are using small molecules
like quantum dots or maybe the wires, quantum
wells or maybe the superlattice technologies.
Organic and dye sensitized solar cells are
often categorized in the third generation
solar cell group.
Third generation solar cell technologies are
at the research and pre-commercial stage because,
yes I will show you some literature into the
next lecture that now how the people are working
and how they are trying to improve the efficiency
of those kind of materials.
Basically, third generation solar cells pursue
more efficiency, more abundant materials,
non-toxic materials and the durability of
that particular systems.
So, types of third generation solar cells
number 1 is called the organic photovoltaic
cell.
So, basically organic photovoltaic cell in
short basically we are calling it as OPV devices
converts solar energy to electrical energy.
A typical OPV device consists of one or several
photoactive materials sandwiched between two
electrodes.
So, basically it is a sandwiched structure;
structure of organic solar cells is like this;
In a bilayer OPV cells, sunlight is absorbed
in into the photovoltaic layers composed of
donor and acceptor semiconducting organic
materials to generate the photocurrents.
So, in this particular image just you see
we are having that sunlight and then top of
that we are having that anode.
We are having that donor layer, acceptor layer,
buffer layer and cathode.
So, in this particular case what happened?
The donor material donates electrons and mainly
the transport holes, acceptor material withdraws
electrons and mainly transport electrons.
So, like this way basically we are getting
the electricity.
So, in this particular case donor layer is
giving the protons which is coming to the
anode.
And, then in this particular case acceptor
level is gives the electrons and it is going
to the buffer layer and to the cathode itself.
And, then automatically one is minus full
of electron, one is the positive one that
is the full of proton and then automatically
the current is passing from the minus to the
plus.
Next mechanism in organic photovoltaic solar
cells.
So, basically photoactive materials harvest
protons from sunlight to form the excitons,
in which electrons are excited from the valence
band into the conduction band which is nothing,
but the known as the light absorption.
Due to the concentration gradient, the excitons
defused to the donor or maybe the acceptor
interface like excitons diffusion and separate
into free holes positive charge carriers and
electrons like negative charge carriers; basically
this mechanism is known as called the charge
separation.
So, if photovoltaic is generated when the
holes and electrons move to the corresponding
electrodes by following either donor or acceptor
phase which is nothing, but known as the charge
extraction.
So, why basically we are using the organic
solar cell?
So, it is very easy to processing, it is having
the very good mechanical flexibility, it is
economically viable, it is very safe to the
environment; so that means, it is does not
create any kind of pollutions to the in environment,
less expensive than the inorganic materials
like silicon.
So, in this particular case we can see that
we have given the examples that how we are
doing light absorptions then exciton diffusion
then charge separation and the charge extraction
how it is taking place.
So, simple it is creating the electron hole
pair the when the electron is moving, then
we are having two collectors, one is collecting
the protons, one is collecting the electrons;
and, then the automatically the current is
moving from one side and then in the loop
also the electron is coming back to its original
positions.
So, like this way they are making the balance
inside the systems and we are getting the
continuous electricity.
And, here basically what the sunlight is doing?
It is agitating that materials to leave the
electron.
Next we are having the dye sensitized solar
cells; till today maximum cases we are using
this means, maximum applications basically
we are using the dye sensitized solar cells.
So, basically the dye sensitized solar cells
in short DSSC or maybe the Gratzel cells named
after the Swiss chemist Michael Gratzel, who
was greatly involved in the development of
new cell types.
Manufacturing of DSSC’s is simple, mostly
low cost and incorporate environmentally friendly
materials.
They have a good efficiency about 10 to 14
percent even under low flux of sunlight.
So that means, if you are having that little
bit cloudy weather also so, by using that
materials you can generate the sunlight.
However, a major drawback is the temperature
sensitivity of the liquid electrolyte.
Hence, a lot of research is going on to improve
the electrolytes performance and the cell
stability.
So, what is the mechanism in the dye sensitized
solar cells?
So, the step 1 is that the dye molecule is
initially in its ground state.
The semiconductor material of the anode is
at this energy level near the valence band
non-conductive.
So, when light shines on the cell, dye molecules
get excited from their ground state to a higher
energy state.
So, simple it is coming from here to here
so that means, S after getting the sunlight
it is moving into the S star.
So, basically the S star is nothing, but the
excited dye molecules having the higher energy
content and overcomes the band gap of the
semiconductor.
The next step the excited dye molecules is
oxidized and an electron is injected into
the conduction band of the semiconductor.
Electrons can now move freely as the semiconductor
is conductive at this energy level.
So, S star is converting into the S plus and
it is releasing one electron to the systems.
Now, electrons are then transported to the
current collector of the anode via the diffusion
process.
An electrical load can be powered if connected.
What is the step 3?
The oxidized dye molecules S plus which is
generating from here is again re-generated
by electron donation from the iodide in the
electrolyte.
So; that means, S plus; 3 by 2 I minus then
again it is become stable so; that means,
it is ready to again become S plus for next
time.
In return iodide is regenerated by reduction
of triiodide on the cathode itself.
So, half I 3 minus plus when it is taking
the electron it is becoming this materials
which is helping to form the again sulphur
over there.
So, its form the again S stable S atom over
there.
So, in this particular case you can see that
we are having the FTO glass and we are having
that platinum counter electrode over there.
So, here it has been clearly shown that how
the electron flow is taking place over there.
If I put the load over there so, I can simply
collect the electricity from this particular
point.
So, in this particular case I am having the
dye synthesized titanium dioxide film.
So, here in this particular case S is nothing
but the titanium so, basically.
So, what is happening over there?
So, sensitizer die so, S plus or maybe the
S minus like this way it is coming from here
to here.
So, you see actually this green; so, when
the green is going into this and then it is
coming I minus and maybe the I 3 minus and
then it is moving to this.
So, actually it is starting from here, it
is going into this and in this particular
case it is coming over here, it is coming
and just to stabilize this particular things
over there.
So, like this way from both the sides it is
coming the material stabilizing into the between,
but the electron is flowing from my FTO flow
glass to the Pt counter or maybe the platinum
counter electrode.
Next is called the quantum dot solar cells;
so, quantum dots are used as the light absorbing
photovoltaic material in solar cells.
Quantum dots have the advantage of tuning
its properties by changing the size of the
nanoparticle.
Yes, because this size you can see dots, dots
means what?
nothing, it is a ball kind of shapes.
So, we while doing the synthesis; basically
we can control the shape of that particular
ball; we can make it smaller, we can make
it bigger also.
This allows them to be easily fabricated to
absorb the different parts of the solar spectrum
making room for efficient harvesting of near
infrared photons.
Quantum dot solar cells use solution process
nanocrystals and useful for the integration
into various solar cells.
So, simple we are having that materials slowly
slowly we are taking out layer by layer and
then after that the smallest part physical
you are getting as a quantum dots.
So, major challenges include inadequate understanding
of surface chemistry of the quantum dots.
So, basically you can see we are having the
titanium dye oxide flow over there and below
that we are using the quantum dot layer such
as the lead sulphide or maybe the lead selenide
or maybe the cadmium sulphide or maybe the
cadmium selenide.
So, these all are the materials where we are
using the contents of this kind of materials
and basically we are using the below of the
TiO2 film.
We are having the transparent conducting electrode,
then we are having that blocking layer.
We are having that counter electrode in this
particular case.
So, what is happening?
The electron is moving from here to here and
the proton is moving from here to here.
It is the conducting electrode will became
the minus and then the counter electrode became
the plus.
So, automatically the current will flow in
this particular case.
Next is known as the nanocrystalline based
solar cells.
So, basically the fullerenes; it is a one
form of the carbon right.
So, have mostly sparked interest as n-type
semiconductor materials in organic field effect
transistors; FET, organic photovoltaic cells.
Fullerenes help electrons travel further in
organic solar cells.
So, basically the carbon nano tubes are used
in the preparation of counter electrodes in
DSSC, Dye Sensitized Solar Cell and transparent
electrode in OPV, organic photovoltaics.
So, basically graphene based ultra thin films
can be used as a new low cost front electrode
material for photovoltaic devices.
The unique geometry of nanowires arrays can
allow for low optical reflection and enhance
the light trapping and absorption within nanowire
arrays.
So that means, the people are working, these
all are the latest materials.
Now, people working on these materials just
to increase efficiency, decrease the cost
and automatically the increase the life of
those particular solar cells so, that we can
use it for a longer time.
Now, come to the comparison of 1st, 2nd and
3rd generation of the solar cells.
So, technology wise 1st generation is the
wafer based, 2nd generation is the thin film
based and 3rd generation is also the thin
film based.
If I talk about the advantages; so, first
generation we are having that high quality,
low defect, high efficiency.
If we talk about the 2nd generations, low
material utilizations and the lower cost;
that means, cost has been reduced.
3rd generations it is non-toxic, it is abundant
materials using, low cost, transparent short
pay back.
And, if we talk about the disadvantages; 1st
generations we are having that high consumption
of active silicon.
If we talk about the 2nd generations scarcity
or toxicity of some materials and if we talk
about the 3rd generations it is optimizing
the lifetime efficiency and cost trade off.
So, automatically now in the 3rd generations
basically we are standing.
So, in this particular case basically you
are trying to increase the efficiency as well
as it will be the low cost.
Next use of the nanotechnology for harvesting
the solar energy.
So, basically in the nanotechnology is a powerful
tool for the host of solar system in support
of efficient, sustainable energy conversion,
storage and conservation in terms of tailoring
the interaction of light with materials and
enabling the processing of low cost semiconductors
into device such as photovoltaics; Making
more efficient photo catalyst for converting
sunlight into chemical fuels; Developing new
materials and membranes for the separation
needed in many energy applications; Converting
chemical fuels into electrical energy and
of course, the vice versa one improving the
energy and power density in batteries.
So, simple nanotechnology what does it mean?
That means, we are dealing the technology
with some nanomaterials.
What is nanomaterials?
It is nothing, but the 10 to the power minus
9 meter.
So, automatically when I am using certain
kind of light absorbing materials or maybe
like any kind of electrode or maybe any kind
of whole transport layer or maybe the electron
transport layer that material basically we
are making like a composites.
So, in that composites we are using certain
kind of filler materials which sizes into
the nanometer range or maybe the nano scale.
So, basically nowadays the people are tending
on to this because due to that high surface
to volume ratio.
So, nanomaterials is very good, it is having
some outstanding properties.
Basically, if we are able to nurture those
materials into the nano levels and people
are using like nanoparticles, nanofibers,
carbon nanotubes, nanosheets, graphene, and
quantum dots.
So, these all are the different types of examples
from the nanotechnology point of view.
Next on which basis basically we are going
to choose that whether this nanomaterials
is good for the solar energy harvesting systems
or not.
So, the ideal candidate materials to be used
in solar cell should possess proper band gap;
so, basically 1.0 to 1.8 electron Volt to
harvest the maximum sunlight.
So, the gap should be like this so, that the
electron can easily jump from one layer to
another layer.
So, valence band to conduction band; good
charge transport property, excellence stability
and the of course the cheap cost.
Now, there are several types of applications
where nowadays we are using the solar energy
directly or maybe the indirectly.
So, charging of the electronic devices; now
we can see that we are having the charger
which is powered by the solar panel.
So, directly the sunlight is coming, it is
generating electricity through that we can
charge our gadgets.
We are having that supplying the power to
the house.
So, top roof basically we are putting the
solar panels over there, we are having that
power source to the outdoor devices, power
to the satellites that is the best examples
nowadays we are using.
Solar powered vehicles, solar powered aero
plane, but just think one that I have given
only the six examples.
But there are n number of examples are there
by which basically we are using the solar
energy, not only that we are using the solar
energy to the automobiles to the ships, to
the marines.
Everywhere nowadays we are using the solar
energy directly so, that we can get the electricity
at the time of scarcity.
Now, we have come to the last slide of this
particular lecture.
So, in summary we can say that to reduce the
pollution from fossil fuels the world is working
on renewable energy sources.
Out of all, solar energy is on top of the
list.
So, basically what is happening?
We are moving from fossil fuels and petroleum
fuels to the renewable solar energy.
Photovoltaic cell converts the light energy
into electricity directly by the photoelectric
effect.
1st generation solar cell energy used single
and polycrystalline silicon material.
2nd generation solar cells are thin film based
and uses less materials, means consumption
of materials is less.
3rd generation solar cells are still in research
and pre-commercial stage.
Carbon nanotubes and graphene are used in
making electrodes in solar cells, also we
are using the graphene quantum dots or maybe
different types of quantum dots.
Nanomaterials are used to enhance the light
capturing from the sun and enhance the performance
of the solar cells.
Thank you.
