Editorial
Dr.Madhuri Sharon
Research Director
Solar Cells: Convert Sunlight into Electricity:
Our global need of energy is derived from coal, gas, oil, and nuclear power plants. These methods are not
very eco-friendly as well as the fossil fuels like oil is a big cause of political instability and threatens peace in the
world, mainly because of the uneven distribution of the oil around the world. Solar energy is being envisaged as
the alternative methods which could compete with the conventional energy production. Conversion of Sun light
to electricity via photovoltaics is being looked at as promising alternative. Three
types of Solar cells are being researched and developed (i) using crystalline
silicon which is most predominantly used solar cell at the moment (ii) thin film
solar cells which include inorganic semiconductors such as CdTe, CdS, etc, which
are also commercially available and (iii) use of organic and organo-metallic
materials. The major concerns of Solar cell technology are to lower the cost, make
it light weight and easy integration to flexible applications. It will not be improper
to say now that use of Solar cell is a viable method to satisfy a substantial amount
of our energy needs while reducing carbon dioxide pollution, creating jobs and
decreasing market instabilities due to the geopolitics of fossil fuels.
This issue of News Letter is an effort to address and highlight the status of solar cells at present by
staff of wcRnb.
“We have this handy fusion reactor in the sky called the sun, you don’t have
to do anything, it just works. It shows up every day.”
Elon Musk, CEO Tesla Motors
Walchand’s effort in harvesting solar energy
Chinmay Phadke Senior Research Fellow
India can be considered as one
of the wealthiest countries in terms of abundance of
solar energy, a raw income from which lots of
revenue can be generated if one learns to use it
wisely. With future concern, it’s absolutely
necessary to understand and develop the
methodologies to venture into the conservation and
utilization of solar energy. Lately, researchers are
putting great efforts for devising highly efficient
solar cell. Till now, many materials like Graphene,
Carbon Nano Tubes etc. have been used for devising
solar cell.
Apart from researchers, few academic
institutes also have gathered interest and have
undertaken the role in harvesting solar energy.
Among the very few to start, the pioneer of
Walchand institutes, Shreeman Dr.Ranjeet Gandhi
has taken a great initiative by installing water heating
systems based on solar as well as the solar generator.
Girl’s hostel, boy’s hostel and the staff quarters are
furnished with the solar water heating facility, which
includes 10 units, each having capacity of heating
1000 Litres of water per day (Lpd) and recently
installed 8 units having 500 Lpd capacity each. This
suffices the daily need of hot water required by
around 900 hostilities as well as the staff.
Also, the college building of Walchand
Institute of Technology (WIT) is supported by 152
solar panels which have the ability of generating 40
kWp to substitute the 200 kWp required by the
institute, thus covers the 20% of the electricity
required by WIT.
Walchand College of arts & science (WCAS) as well
as WIT campus roads are provided with the solar
power driven lights, which have been installed
throughout campus. With these solar devices lots of
energy or electricity can be redeemed. WCAS and
WIT serves as a noteworthy example for its
contribution in conservation and elegant use of solar
energy.
INCREDIBLE INDIA’S EFFORTS INTO COMMERCIALLY
GENERATING ELECTRICITY BY HARNESSING SOLAR POWER
Nallin Sharma Senior Research Fellow
India is one of leading nation in
every aspect to Humanity, from basic education to
empowering high end industries of world. Demands
of world are again hooked up to Indian Scientists,
Engineers, Doctors and even grass level skilled man-
power to meet the global need in vivid sectors of
engineering like Power/Energy solutions, for
chemical industries, IT & for Mechanical
engineering fields.
Current need to us is green & clean energy
sources, topping in this list is Solar Energy. India is
again a strong contender in world scenario for both
manufacturing Solar panels as well generating &
distributing this clean energy to masses. Twenty first
century is witnessing several large solar projects
being are engineered to fulfill power crisis.
Now we have more than 200 heavy running
solar panel manufacturing industries, situated all
over India; to name a few:
(i)Vikram Solar of Kolkata W. Bengal; which is
since 2006 having 500MW/annum production and
have installed 120 projects in India. Their future plan
is to enter in producing Nano Carbon incorporated
solar panels for having higher efficiency
(ii)Bergen Associates in Delhi have provided solar
power to 50 villages across India,
(iii)Moser Baer Solar LTD of Delhi
(iv)Tata Power Solar System, Bengaluru, Karnataka,
they coming up with Nano Carbon engineered solar
panels promising in producing energy more
efficiently. According to Ashish Khanna, CEO of
Tata Power Solar; “There are 300 million people in
India without power; 400 million people are supplied
erratic power; more than half the population of India
does not get proper power,” therefore, the
government of India’s ambitious target of achieving
100 GW solar power capacity by 2022 is the need of
the day and future.
(v)Sun solar Techno LTD in Mulund, Mumbai of
Maharashtra,
(vi)Luminous Power Technologies of Pune,
Maharashtra
(vii)Surana solar of Hyderabad, Telangana have also
shown interest in developing Nano Carbon
incorporated solar cell and panels.
(viii)Vorks Energy in Noida, UP
(ix)JJ PV Solar situated in Rajkot Gujarat etc…….
Majority of these companies are specialized
in producing up to 300W Mono & Polycrystalline
panels. They have benchmarked priority not to just
the govt. certifications such as ISO 9000, 9001,
14001; but daily & heavy users also.
Now the challenge is to provide cheaper
installation and production. The next big leap in our
solar distribution is to slash the Rupee 20 per unit
cost to deep down at Rupee 0.2/unit. However, the
current cost as per IREDA is Rupee 5.5 per unit.
Policies have come up to encourage domestic user by
not just providing subsidy but low power consuming
electrical commodities like LED bulbs, low cost
induction heaters, high efficiency electrical
regulators, etc. Tight clashes between Solar powered
Air-conditioner system & reliable Electric vehicle is
one big project where solar power giants are turning
up.
However, summary of study by Deloitte and
Confederation of Indian Industry (CII) has revealed
that though India has installed solar power capacity
by March 2015 is 3,744 MW, still India is not
harvesting even 1% of its total energy. This
statement is disheartening as well as encouraging. It
tells us that we have such a vast store of solar energy
available. And India has to concentrate on policy
issues and challenges, new and emerging
technologies, grid evacuation, availability and load
dispatch and innovative financing models in the solar
power sector.
Dye-Sensitized Solar Cells: A Need for Future Energy Demand
Dr. Rakesh Afre H.O.D Nanotechnology
Dye-sensitized photovoltaic (PV) solar cells
(DSC), a non-conventional PV technology, which
was first reported in 1991, have shown electrical
conversion efficiencies greater than 10% in
laboratory testing. The rising population, rapidly
changing life styles of people, heavy
industrialization and changing landscape of cities has
enormously increased the energy demands. The
present annual worldwide electricity consumption is
12 TW and is expected to become 24 TW by 2050,
leaving a challenging deficit of 12 TW. The present
energy scenario of using fossil fuels to meet the
energy demand is unable to meet the increase in
demand effectively, as these fossil fuel resources are
non-renewable and limited. Also, they cause
significant environmental hazards, like global
warming and the associated climatic issues. Hence,
there is an urgent necessity to adopt renewable
sources of energy, which are eco-friendly and not
extinguishable. Of the various renewable sources
available, such as wind, tidal, geothermal, biomass,
solar, etc., solar serves as the most dependable
option. Solar energy is freely and abundantly
available. Once installed, the maintenance cost is
very low. It is eco-friendly, safely fitting into our
society without any disturbance.
Producing electricity from the Sun requires the
installation of solar panels, which incurs a huge
initial cost and requires large areas of lands for
installation. This is where nanotechnology comes
into the picture and serves the purpose of increasing
the efficiency to higher levels, thus bringing down
the overall cost for energy production. Also,
emerging low-cost solar cell technologies, e.g. thin
film technologies and dye-sensitized solar cells
(DSCs) can help to replace the use of silicon, which
is expensive. Again,
nanotechnological implications can be applied in
these solar cells, to achieve higher efficiencies.
A dye sensitized solar cell is based on a
semiconductor formed between a photo-sensitized
anode and an electrolyte, a photo-electrochemical
system. Dye sensitized cells are used for converting
sunlight into electrical energy across a wide intensity
range by using a dye, which is absorbed in titanium
oxide semiconductor. A dye sensitized cell has
several attractive features such as semi-flexibility
and semi-transparency, which offers a variety of
uses. In the current scenario, dye sensitized cells are
the most efficient third generation solar technology
available. Dye sensitized cells can be a suitable
option as a replacement for existing technologies in
low density applications such as rooftop solar
collectors. However, use of liquid electrolyte in dye
sensitized cell design is a major drawback, as it has
temperature stability problems. In the last 5-10 years,
solid-state dye sensitized solar cells have been
developed. In this case the liquid electrolyte is
replaced by one of the several solid hole-conducting
materials. During this period, the efficiency of solid
state dye sensitized solar cell has increased from 4%
to 15%.
Based on application, the global dye sensitized cell
market is segmented into different categories:
building-integrated photovoltaics, indoor
application, retail application, emergency power and
military application, and others. Building-integrated
photovoltaics are further sub-segmented into BIPV
glass and solar roofs. Indoor application is further
Green House using Dye-sensitized Solar
Cell
sub-segmented into three categories: solar chargers,
wireless keyboards, and others. Retail application is
further sub-segmented into three categories: indoor
and outdoor advertising, point-of-purchase displays,
and others.
The need to replace fossil fuels with renewable and
sustainable energy sources is more exigent than ever,
in order to reduce CO2 emissions causing climatic
change and guarantee the further development of
mankind in harmony with our natural environment.
Can Silicon solar cell be replaced by Carbon solar cell?
Prof. Dr. Maheshwar Sharon Joint Research Director
Conversion of Solar energy to electricity is
now a viable method with many advantages over
conversion of fossil energy to electricity such as
reduced carbon dioxide pollution, creating jobs and
decreasing market instabilities due to the geopolitics
of fossil fuels. Moreover fossil fuel supplies are
rapidly diminishing.
The first credit for developing a Solar Cell
goes to Becqurel who discovered photovoltaic effect
in selenium way back in 1839. Other early
contributors were W. Zerassky (1908), who built a
solar thermoelectric device by welding two
dissimilar metals i.e. zinc antimony alloy and silver
plated alloy. Hailing the solar energy as Green
technology and need of the day Daryl Chapin, Calvin
Fuller and Gerald Pearson of Bell Laboratories
developed the first solar cells in 1954. Now the
efforts are on to achieve commercially competitive
electricity generation with sources such as oil or coal.
The requirements for grid parity vary widely,
depending on local factors such as the annual number
of Sun hours as well as the local costs of competing
technologies to get higher conversion of sun light. It
is theoretically predicted that photovoltaic cell can
give efficiency up to 30%. Successful use of Solar
Cell was in 1959 when Vanguard satellite carried
first 108 solar photovoltaic chips to power its radio.
It must be mentioned here that for such project cost
of Solar cell was immaterial.
When scientists realized that the petrol and
other fossil fuels from which electrical power is
being generated has limited availability, they
indulged in developing photovoltaic Solar Cell that
will be useful for terrestrial application. Initially the
cost of Solar Cell was very high ($1000/w).
However, with consistent effort of scientists it was
reduced to about $100/w by 1970; and now it is
around $5/w. Efforts are now made to develop
silicon solar cell from amorphous silicon so that
flexible type solar cell could be possible. Efforts are
also made to develop materials other than silicon like
CdSe,CuInSe2 etc for making solar cell. These solar
cells are also known as solid state solar cell formed
by joining n- and p-type of these materials like n-Si
with p-Si. Anew class of solar cell was developed
during 1966 when a semiconductor-metal could form
similar junction as p;n junction. This discovery was
made by Walter H. Schottky and is classified as
metal-Schottky type junction. Fujishima and Honda
in 1972 showed a possibility of making similar solar
cell by using electrolyte in between the two materials
i.e. n-Si/electrolyte/metal. Such cells were classified
as wet type solar cell or Photoelectrochemical solar
cell.
This discovery gave the birth to a concept
that a metal-Semiconductoor Schottky type junction
could also be formed by bringing a suitable
electrolyte in between either two semiconductors
(i.e. p-type and n-type) or in between semiconductor
and metal. Global scientists while working on this
type cell realised that though it was possible to
fabricate wet type cell which could compete with
photovoltaic solar cell, but unfortunately there is non
inorganic semiconductor material which could be
electrochemically and photoelectrochemically stable
in aquous solution for more than few hours to few
months. This was the biggest hurdle towards the
development of wet type solar cell.
While scientists were looking for the
solution to this problem, discovery of fulleren by
Kroto et al in 1985 (Kroto along with Smalley and
Robert Curl got Nobel prize in 1996 for this
discovery) gave a light of hope that carbon
nanomaterial could be a good choice for devloping
wet type solar cell, because carbon material is
expectd to be stable in acidic as well as alkaline
media.
Considering this Sharon’s group got
indulged in early nineteen nintees into developing
semiconducting carbon for its application in wet
type of cell. Sharon’s group questioned that if
elecrolyte can give a Schottky type junction then why
not it can also formed ohmic type junction. Answer
to this question resulted in developing solar
chargeable battery, which they coined as Saur
Viddyut Kosh) and Sharon-Schottky Juntion.
The challenge to get a material, which is
electrochemically and photoelectrochemically
stable, remained a challenge when it was realised that
almost all semiconducting nano carbon materials
possess zero band gap (indirect band gap). Though
Sharon’s group could find a synthethetic process to
develop carbon of direct band gap 1.4 eV (which is
most suitable band gap for wet type solar cell), but
presence of zero indrect band gap caused the major
hurdle in decreasing the concentration of minority
carrier. However, they are the only group in the
world to have developed a Homojunction Carbon
Solar Cell with an efficiency of 4%, but unless the
zero indirect band gap is either destroyed or its band
gap is increased to some reasonable value, future of
carbon photovoltaic solar cell remain as biggest
hurdle in competeing with silicon solar cell. This
group no doubt is still working with a hope to solve
this problem, only time will give the real answer of
their success.
Some humble efforts of our group: 1. M. Sharon; Solar Galvanic Cell, Industrial Research. May, 1976 (USA).
2. M. Sharon, S. G. Saran, A. Sinha & B. M. Prasad; A Saur Viddyut Kosh-Solar Photogalvanic Cell - II., J.
Electrochem. Soc. 30(3), 200-203, 1981.
3. M. Sharon & A. Sinha; A rechargeable Photoelectrochemical Solar Cells., Int. J. Hydrogen Energy, 7,
557-562, 1982.
4. M. Sharon, S. Kumar & S. R. Jawalekar; Saur Viddyut Kosh-IV, Study of a rechargeable solar battery
with n-Pb3O4 electrodes., Solar Cells. 12-4, 353 - 361, 1984
5. M. Sharon & G. R. Rao, Photoelectrochemical cell with liquid- (ohmic)-semiconductor- liquid (Schottky
Barrier) system, Ind. J. Chem. 25A, 170 - 172, 1986.
6. M. Sharon, P. Veluchamy, C. Natrajan & D. Kumar, Review Article - Solar Rechargeable Battery -
Principle and Materials, Electrochimica Acta 36 (7), 1107 -11026, 1991.
7. M. Sharon, K. Mukhopadhyay, K. M. Krishna, Fullerenes from camphor: A Natural Source., Phys.
Rev. Lett. 72(20), 3182 – 3185, 1994
8. M. Sharon, I. Mukhopadhyay and K. Mukhopadhyay, A Photoelectrochemical Solar Cells from p-Carbon
semiconductor, Sol. Energy Mat. Sol. Cells, 45, 35-41, 1997
9. M. Sharon, K. Mukhopadhyay, I. Mukhopadhyay, T. Soga and M. Umeno, Carbon Photovoltaic cell,
Carbon, 35, 863-864, 1997
10. M. Sharon, K. M. Krishna, T. Soga, K. Mukhopadhyay, M. Umeno, Photovoltaic solar cell from
camphoric carbon. A natural Carbon, Solar Energy Materials and Solar cells, 48, 1-4, 25-33, 1997
CARBON NANOTUBES: A POTENTIAL MEMBER IN THE SOLAR ENERGY
TECHNOLOGY
Isaac Nandgavkar Junior Research Fellow
Carbon nanotubes (CNTs)
are allotropes of carbon having dimension in the
nanometer range. They have tube-like structure
composed of carbon atoms linked in hexagonal
shapes with each covalently bonded to 3 other carbon
atoms. Carbon Nanotubes have many structures,
differing in length, thickness, and in the type of
helicity and number of layers. As a group, CNTs
typically have diameters ranging from <1 nm up to
50 nm. Their lengths are typically several microns,
but recent advancements have made the nanotubes
much longer measuring in centimeters. Overall,
Carbon Nanotubes show a unique combination of
stiffness, strength, and tenacity compared to other
fiber materials which usually lack one or more of
these properties. Thermal and electrical conductivity
are also very high and comparable to other
conductive materials. CNTs are from the fullerene
family whose name is derived from the long, hollow
structure with the walls formed by one-atom-thick
sheets of carbon, called graphene. These sheets are
rolled at specific and chiral angles, and the
combination of the rolling angle and radius decides
the CNT’s properties; for example, whether the CNT
is a metal or semiconductor.
Entry of CNT in Solar Cell Arena
CNTs possess a wide range of direct band
gaps matching the solar spectrum, strong photo
absorption, from infrared to ultraviolet, high carrier
mobility and reduced carrier transport scattering,
apart from this, they are also lighter, more flexible
and cheaper than conventional solar-cell materials
thus ideal for photovoltaic technology. But research
stalled when CNTs proved to be inefficient,
converting far less sunlight into power than other
methods.
In the earlier years, the researchers tended to
choose one particular chirality with good
semiconducting properties and build an entire solar
cell out of that one. But the problem is that each CNT
chirality absorbs a narrow range of optical
wavelengths. So if the CNTs of a single chiral
structure is used it would mean throwing way all the
other solar energy. In the preceding paragraphs some
milestone achievement in recent years are presented
Researchers at Umeå University in Sweden
[March 2014] have discovered that controlled
placement of the CNTs into nano-structures
produces a huge boost in electronic performance. For
the first time, the researchers show that CNTs can be
engineered into complex network architectures, and
with controlled nano-scale dimensions inside a
polymer matrix. The high degree of control of the
method enables production of highly efficient CNTs
networks with a very small amount of CNTs
compared to other conventional methods, thereby
strongly reducing materials costs. The resulting nano
networks possess exceptional ability to transport
charges, up to 100 million times higher than
previously measured CNT random networks
produced by conventional methods.
There has been a breakthrough for the CNTs,
paving their way back into the field of solar
technology in September 2014, when few
researchers in Northwestern University published
about polychiral semiconducting CNTs solar cells
having higher efficiency than predecessors.
Addressing the problem of single chiral not able to
absorbs wide range of wavelengths, these researchers
synthesized a polychiral CNT which maximized the
amount of photocurrent produced by absorbing a
broader range of solar-spectrum wavelengths. The
cells significantly absorbed near-infrared
wavelengths, a range that has been inaccessible to
many leading thin-film technologies.
A new technique is developed in November
2014 using hydrogen fluoride and electric current to
remove oxygen from CNTs which resulted in high
power conversion efficiencies, a measure of how
efficiently a solar cell converts sunlight to electric
energy.
As reported in a published article in
ChemNanoMat in February 2015, a thin conducting
polymer interlayer significantly improves
photovoltaic performance by creating a better
depletion layer within the underlying silicon. With
the addition of a top antireflection layer, a
photovoltaic device, silicon-poly(3,4-
ethylenedioxythiophene): poly(styrene sulfonate)–
carbon nanotube–poly(styrene) has been fabricated
with a photovoltaic conversion efficiency of 8.7 %.
In February 2015, researchers in Japan
demonstrated a significant improvement in the CNT
solar cells by the use of metal oxide layers for
efficient carrier transport. As a result the power
conversion efficiency improved up to 17% in
CNT/Si solar cells.
Researchers at the University of Cincinnati
(March 2015) presented on how a blend of
conjugated polymers resulted in structural and
electronic changes that increased the efficiency
three-fold, by incorporating pristine graphene into
the active layer of the carbon-based materials. This
research has shown potential for constructing
flexible solar cells using CNTs, researchers have
found that wrapping carbon nanotubes in non-
covalently bonded polymers improves their
photovoltaic functions in solar cells.
In a recent effort in April 2015 Schottky
diodes and solar cells are statistically created in the
contact area between two macroscopic films of
single-walled carbon nanotubes (SWCNTs) at the
junction of semiconducting and quasi-metallic
bundles consisting of several high quality tubes. The
n-doping of one of the films allows for photovoltaic
action, owing to an increase in the built-in potential
at the bundle-to-bundle interface. Statistical analysis
demonstrates that the Schottky barrier device
contributes significantly to the I-V characteristics,
compared to the p-n diode. The upper limit of
photovoltaic conversion efficiency has been
estimated at ∼20%, demonstrating that the light
energy conversion is very efficient for such a unique
solar cell. While there have been multiple studies on
rectifying SWNT diodes in the nanoscale
environment, this is the first report of a macroscopic
all-CNT diode and solar cell.
In September 2015, for the first time,
scientists have created a solar energy collector using
CNTs that can directly convert optical light in to a
direct current. It is hoped these optical rectennas may
one day rival established technologies, such as the
silicon solar cell.
One of the most recent outcome of improving
power conversion efficiency (PCE) of organic solar
cells by the addition of small quantities (0.02%–
0.04%) of pristine single-walled carbon nanotubes
(SWCNTs) in the active-layer is reported in this
month of December 2015. A single diode model of
a solar cell was used to extract the cell parameters
and understand the effect of SWNTs. Based on
experimental data and it's fitting to the single diode
model, they proposed that SWCNT improved the
transport and extraction of photo generated charges
within the solar cell device.
GRAPHENE – A 2-DIMENSIONAL CARBON TO ENHANCE
THE SOLAR ENERGY CONVERSION CAPACITY TO ELECTRICITY
Farha Modi Junior Research Fellow
Graphene, the pure carbon
material that is just one atom thick and nearly
transparent when laid out in sheets, manages to be
roughly 200 times stronger than steel. It is also an
excellent conductor of energy and can be synthesized
from unique carbon sources, anything from pencil
lead and it has thousands of applications like in
batteries, computer circuits, smartphones, energy
cells, etc. When you search “graphene” on the web,
the most common picture you’ll see is a molecular
lattice that resembles a honeycomb. In reality, this
depiction of graphene is perhaps the best way to
understand its incredible properties. The structure is
remarkably strong and efficient. As such, graphene
is the most chemically reactive form of carbon,
which also makes the material highly conductive and
flexible, as well as strong. Graphene is an insanely
amazing conductor of heat and electricity but, up till
now it wasn’t very good at absorbing light. A very
big problem currently with a graphene based solar
panel design is the fact that the edges of the graphene
sheet are highly reactive, so harvesting the current
would prove to be much more of a challenge.
One of the major reasons that solar panels are
facing such hurdles to replace conventional
electricity sources is because they are very
inefficient. The most efficient and the most
expensive panel is currently somewhere around 32%
efficiency. However, scientists in Switzerland, Ecole
Polytechnique Federale de Lausanne (EPFL) have
figured out a way to utilize Graphene in solar panel
design, raising its efficiency to an absolutely
staggering 60 % - a finally feasible amount.
A few years ago in April 2012, scientists
from Michigan Technological University found out
that incorporating graphene, one of the coolest new
nanomaterial of the 21st century could increase the
cell’s conductivity and also boost the efficiency of
the next generation of solar panels, bringing 52.4%
more current into the circuit.
Last year in January, 2014, Juan Bisquert,
Professor of Applied physics at University of Jaume
I in Castello, created and characterized a
photovoltaic device based on a combination of
titanium oxide and graphene- a charge collector and
perovskite as sunlight absorber. The device is
manufactured at low temperatures and has a high
efficiency. Researchers from University of Illinois
College of Engineering had achieved new levels of
performance (March 24, 2014]) for seed-free and
substrate-free arrays of nanowires from class of
materials called III-V directly on graphene. These
semiconductor compounds hold particular promise
for applications involving light, such as Solar cells or
lasers.
In this image,
imagine a field of small
wires, standing at
attention like a tiny
field of wheat,
gathering the Sun’s rays
as the first step in Solar
energy conversion.
Scientist at Michigan Technological
University (August, 2014) tried to overcome few
drawbacks of solar cells by replacing platinum ( a
key material in dye-sensitized solar cells) with a new,
3-D form of graphene made from carbon monoxide
and lithium oxide with virtually no loss in electrical
generating capacity.
Very recently in November, 2015 it is
reported that a Researcher at the Hong Kong
Polytechnic University has developed a first-ever
made semitransparent perovskite solar cells with
graphene as electrode. With simple processing
techniques, solar cells with high power conversion
efficiencies can be fabricated at low cost. The power
conversion efficiencies of this novel invention was
around 12% when they were illuminated from
Fluorine-doped Tin Oxide bottom electrodes (FTO)
or the graphene top electrodes, compared with 7% of
conventional semitransparent solar cells. Its potential
low cost of less than HK$0.5/Watt, more than 50%
reduction compared with the existing cost of silicon
solar cells, will enable it to be widely used in the
future. Semitransparent solar cell technology can be
integrated into the building design, replacing
conventional building material, such as facades,
shelters, windows and rooftops, etc.
The “Super material” isn’t ready yet,
but it is going to make future technologies so awesome.
DYE SENSITIZED SOLAR CELL – A THIN FILM SOLAR CELL
Prerak Patel Junior Research Fellow
A dye-sensitized solar cell (DSSC), also s referred to
as dye sensitized cells (DSC) is a low-cost solar cell
belonging to the group of thin film solar cells. These
are a third generation photovoltaic (solar) cell that
converts any visible light into electrical energy. This
new class of advanced
solar cell can be likened to
artificial photosynthesis
due to the way in which it
mimics nature’s absorption
of light energy.
It is based on a
semiconductor formed between a photo-sensitized
anode and an electrolyte, a photo electrochemical
system. The modern version of a dye solar cell, also
known as the Grätzel cell, was originally invented in
1988 by Brian O'Regan and Michael Grätzel at UC
Berkeley and this work was later developed by the
afore mentioned scientists at the École
Polytechnique Fédérale de Lausanne until the
publication of the first high efficiency DSSC in 1991.
Michael Grätzel has been awarded the 2010
Millennium Technology Prize for this invention.
DSSC is a disruptive technology that can be
used to produce electricity in a wide range of light
conditions, indoors and outdoors, enabling the user
to convert both artificial and natural light into energy
to power a broad range of electronic devices.
Dye-sensitized solar cells have gained
widespread attention in recent years because of their
low production costs, ease of fabrication and tunable
optical properties, such as color and transparency. In
DSSC, electrodes consist of sintered semiconducting
nanoparticles, mainly TiO2 or ZnO. These
nanoparticle DSSCs rely on trap-limited diffusion
through the semiconductor nanoparticles for the
electron transport.
This limits the device efficiency since it is a
slow transport mechanism. Recombination is more
likely to occur at longer wavelengths of radiation.
Moreover, sintering of nanoparticles requires a high
temperature of about 450°C, which restricts the
fabrication of these cells to robust, rigid solid
substrates. It has been proved that there is increase in
the efficiency of DSSC, if the sintered nanoparticle
electrode is replaced by a specially designed
electrode possessing an exotic 'nanoplant-like'
morphology.
Some of the recent mile-stone out puts in DSSC
are enumerated below:
2010
The world witnessed a major breakthrough
when researchers at the École Polytechnique
Fédérale de Lausanne and at the University du
Québec à Montréal claim to have overcome two of
the challenges faced in DSC's (i) "New molecules"
were created for the electrolyte, resulting in a liquid
or gel that is transparent and non-corrosive, which
can increase the photo voltage and improve the cell's
output and stability; (ii) At the cathode, platinum was
replaced by cobalt sulfide, which is far less
expensive, more efficient, more stable and easier to
produce in the laboratory.
2011
World´s largest dye sensitized photovoltaic
module, printed onto steel in a continuous line was
announced by Dyesol and Tata Steel Europe in June.
Immediately after that in October Dyesol and CSIRO
announced a successful completion of Second
Milestone that was explained by Dyesol Director
Gordon Thompson as, "The materials developed
during this joint collaboration have the potential to
significantly advance the commercialization of DSC
in a range of applications where performance and
stability are essential requirements. Dyesol is
extremely encouraged by the breakthroughs in the
chemistry allowing the production of the target
molecules. This creates a path to the immediate
commercial utilization of these new materials."
Dyesol and Tata Steel Europe in November 2011
achieved the targeted development of Grid Parity
Competitive BIPV solar steel that does not require
government subsidized feed in tariffs. TATA-Dyesol
"Solar Steel" Roofing is currently being installed on
the Sustainable Building Envelope Centre (SBEC) in
Shotton, Wales.
2012
Northwestern University researchers
announced a solution to a primary problem of DSSCs
that of difficulties in using and containing the liquid
electrolyte and the consequent relatively short useful
life of the device. This is achieved through the use of
nanotechnology and the conversion of the liquid
electrolyte to a solid. The current efficiency is about
half that of silicon cells, but the cells are lightweight
and potentially of much lower cost to produce.
2013
During the last 5–10 years, a new kind of
DSSC has been developed - the solid state dye-
sensitized solar cell. In this case the liquid electrolyte
is replaced by one of several solid hole conducting
materials. From 2009 to 2013 the efficiency of Solid
State DSSCs has dramatically increased from 4% to
15%. Michael Graetzel announced the fabrication of
Solid State DSSCs with 15.0% efficiency, reached
by the means of a hybrid perovskite CH3NH3PbI3
dye, subsequently deposited from the separated
solutions of CH3NH3I and PbI2.
2014
At University Malaya, Dr. Wee Siong Chiu
and colleagues were working on controlling the
secondary nucleation and self-assembly in zinc oxide
(ZnO), a material which is currently being
scrutinized for its potential applications in dye-
sensitized solar cells as well as photo catalytic
reactions to generate clean electricity by splitting
water under sunlight. In this work, Dr. Chiu and
Alireza Yaghoubi demonstrated a new route for
synthesis of various zinc oxide nanostructures using
the lipophilic interactions between a novel precursor
and a number of fatty acids. They are hoping to
further use this method to increase the efficiency of
photo catalysts in the visible regime where most of
the sunlight energy lies. According to the
researchers, if this approach is successful, generating
electricity is as easy as pouring some bio-inert
nonmaterial into a lake and fusing the split oxygen
and hydrogen atoms back into water in a photo
electrochemical cell.
2015
Yiying Wu, professor of Chemistry &
Biochemistry at Ohio State University have
developed the first aqueous flow battery with solar
capability. This solar flow battery design can
potentially be applied for grid-scale solar energy
conversion and storage, as well as producing
‘electrolyte fuels’ that might be used to power future
electric vehicles,” In tests, the researchers compared
the solar flow battery’s performance to that of a
typical lithium-iodine battery. They charged and
discharged the batteries 25 times. Each time, both
batteries discharged around 3.3 volts. The difference
was that the solar flow battery could produce the
same output with less charging. The typical battery
had to be charged to 3.6 volts to discharge 3.3 volts.
The solar flow battery was charged to only 2.9 volts,
because the solar panel made up the difference.
That’s an energy savings of nearly 20 percent. This
Solar panel is called dye-sensitized solar cell or, as
Wu and his team have dubbed it, the first “aqueous
solar flow battery.”
“Prototype aqueous solar
flow battery under
development at The Ohio
State University. The square
piece of solar cell is red,
because the researchers are
using a red dye to tune the
wavelength of light it
absorbs and converts to
electrons.”
Giuseppe Calogero and his team have developed
vegetable based dye-sensitized solar cells. Vegetable
dyes, extracted from algae, flowers, fruit and leaves,
are being used as sensitizers in DSSCs. Thus far,
anthocyanin and betalain extracts together with
selected chlorophyll derivatives are the most
successful vegetable sensitizers
Contact Information
Address: Walchand Centre for Research in Nanotechnology
& Bio-nanotechnology, Walchand College of Arts & Science,
W.H. Marg, Ashok Chowk, Solapur – 413006.
Website: www.wcrnb.com
Email: [email protected] Office No.: 0217-2651863
(A leading Institution Developing Nanotechnology)
Of
Walchand College of Arts & Science, Solapur
is starting M.Sc. in Nanotechnology from June 2016
This course is designed to provide you with the knowledge, skills & practical experience
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