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International Journal of Electrical Electronics & Science Engineering Volume 1, Issue 5 (October 2014), ISSN : 2348 2273 Available Online at www.ijeecse.com

Nano Solar Cells: Advantages and Applications

Shaik Ameer, Kosuri Venkateswara Rao,Shashi Shekhar Chaubey, Setty Abhinav Andhra Loyola institute of engineering and technology,Vijayawada, Andhra Pradesh, India [email protected],[email protected], [email protected], [email protected]

Abstract: This paper will discuss the science of nanowire technology in the field of . It will elaborate on how this recent innovation improves upon the current methods in efficiency, cost, and durability. The value of this technology to its field, and its ability to make a viable worldwide option will also be discussed. It is estimated that the world’s supply of fossil fuels will be reduced to a bare minimum during this century. Renewable energy sources such as wind and solar energy have yet to become major contributors to our energy supply due to their cost and efficiency. Presently, nanotechnology is being introduced into the field of solar energy to combat this fault and improve both efficiency and cost. Nanowire solar cells that have already been developed are mostly based on hybrid organic-inorganic materials or are made of . Presently the efficiency produced two main challenges; therefore, much work is being done to by the traditional based solar cells is make an all solid state DSSC. approximately 6.5%. These first attempts at using nanowires in solar cells have increased this efficiency up to 8.5%. New technologies are looking into all-inorganic solar cells based on silicon nanowires. The silicon nanowires are relatively easy to synthesize and can be used with low cost substrate technologies like glass and metal foil. These low cost substrates will allow the nanowires to be not only durable but also much easier to produce than current silicon base solar cells]. Overall the continued developments in fields such as this are crucial if we as a nation are committed to securing the stability of our economy.

Keywords: Nanotechnology, Nanowires, Photovoltaic cells, Renewable resources, Solar cells, Solar energy I. INTRODUCTION Nano technology might be able to increase the efficiency of In addition, the use of solvent free electrolytes in the DSSC is solar cells, but the most promising application of nano expected to offer stable performance for Conventional solar technology is the reduction of manufacturing cost. The cells are called photovoltaic cells. These cells are made out conversion efficiency of dye-sensitized solar cells has of semiconducting material, usually silicon. When light hits currently been improved to above 11%. DSSCs with high the cells, they absorb energy through . This absorbed conversion efficiency and low cost. energy knocks out in the silicon, allowing them to flow. By adding different impurities to the silicon such as Nano technology might be able to increase the efficiency of phosphorous or boron, an electric field can be established. solar cells, but the most promising application of nano This electric field acts as a diode, because it only allows technology is the reduction of manufacturing cost. electrons to flow in one direction. Consequently, the end The conversion efficiency of dye-sensitized solar cells has result is a current of electrons, better known to us as currently been improved to above 11%. DSSCs with high electricity. Conventional solar cells have two main draw conversion efficiency and low cost have been proposed as backs: they can only achieve efficiencies around ten percent alternative to silicon based photovoltaic. and they are expensive to manufacture. The first drawback, inefficiency, is almost unavoidable with silicon cells. This is The encapsulation problem posed by the use of the liquid because the incoming photons, or, light, must have the right electrolyte based DSSCs, solvent leakage and evaporation are energy, called the energy, to knock out an . 20

International Journal of Electrical Electronics & Computer Science Engineering Volume 1, Issue 5 (October 2014), ISSN : 2348 2273 Available Online at www.ijeecse.com

If the has less energy than the band gap energy then it have also been investigated. Attached to the surface of the will pass through the device. Plastic and solid state DSSCs naocrystalline film is a monolayer of the charge transfer dye. incorporating single walled nano tubes and imidazolium Photo excitation of the latter results in the injection of a iodide derivative has been fabricated. The introductions of electron into the conducting band of the oxide. The original carbon nano tubes improve performance through reduction of state of the dye is subsequently restored by an electron the series resistance. TiO2 coated CNTs were recently used in donation from the electrolyte, usually an organic solvent DSSCs. Compared with a conventional Tio2 cell, a TiO2- containing redox system, such as the iodide/trioxides couple. coated CNT cell gives an increase in short circuit current The generation in turn by the reduction of triiodide at the density , resulting in 50% increase in conversion efficiency. counter electrode the circuit being completed via electron migratin through the external load. The voltage generated under illumination corresponds to the difference between the Fermi level of the electron power from light without suffering any permanent chemical transformation.

A recent alternative embodiment of the DSC concept is the sensitized usually with an in organic wide band gap nanocrystalline of n-type polarity as electron acceptor, the charge neutrality on the dye being restored by anhole delivered by the complememntary semiconductor, inorganic or organic and of p-type polarity. The prior photo-electrochemical variant, being further advanced in development, has an AM 1.5 solar conversion efficiency of over 10%, while that of the solid state device is, yet, significantly lower

According to the United States Geologic Survey, the world II. DYE-SENSITIZED NANOCRYSTALLINE SOLAR reserve of Te is 47,000 tons. CELL (DSC) If all of it was used to make solar cells, we could generate 0.68 TW during peak conditions or about 0.14 TW averaged A schematic presentation of the operating principles of the throughout the day. We want >5 TW. The Reserve is defined DSC is given in fig. as the amount that can be economically recovered. Te is a byproduct of Cu mining. As the price goes up, more Cu plants will install equipment to capture the Te. Until recently, no known Te ores were known. We might find a lot more Te when we look for it.

The sun gives us 1 kW/m2, so a 10 % efficient module producesAt the heart of the system is a mesoporous oxide layer composed of nanometer-sized particles which have been sintered together to allow for electronic conduction to takes place. The material of choice has been TiO2 although alternative wide band gap oxides such as ZnO and Nb205 21

International Journal of Electrical Electronics & Computer Science Engineering Volume 1, Issue 5 (October 2014), ISSN : 2348 2273 Available Online at www.ijeecse.com

III. MARTIN GREEN’S GENERATIONS OF PV constituents of the nano crystalline injection solar cells, that is, TECHNOLOGY the conducting glass the TiO2 film, the sensitizer, the electrolyte, the counter electrode and the sealent has therefore been subjected to close scrutiny. The stability of the TC glass and the nano crystalline Tio2 film being unquestionable investigations have focused on the four other components. As a pure solid the N3 dye is stable even in air up to 280ºC where decarboxylation sets in. upon long time illumination it sustained 108 redox cycles without noticeable loss of performance corresponding to 20 years of continuous operation in natural sunlight. The reason for this outstanding stability is the very rapid deactivation of its excited state via charge injection into the Tio2 occurs in the femtosecond time domain. This is at least eight orders of magnitude faster than the any other competing channels of excited state deviation including those leading to chemical transformation of the dye. The oxidized state of N3/N3+ couples shows reversible If the radiative lifetime is short, a photon can be absorbed and electrochemical behavior in different organic solvents re-emitted > 50 times before the free carriers are collected. indicating that the life time of N3+ is at least several seconds under these conditions. However when maintained in the IV. PRESENT DSC RESEARCH AND oxidized state the dye degrades through loss of sulfur. DEVELOPMENT Regeneration of the N3 in the photo voltaic cell should therefore occur rapidly, i.e. within the nanosecond or micro Panchromatic sensitizers: Upon excitation it should inject seconds to avoid this unwanted side reaction. Lack of electrons into the solid with a quantum yield of unity. The adequate conditions for regeneration of the dye has led to cell energy level of the excited state should be well matched to the failure. lower bound of the conduction band of the oxide to minimize energetic loses during the electron transfer reaction. Its redox potential should be sufficiently high that it can be regenerated via electron donation from the redox electrolyte or the hole conductor. Finally, it should be stable enough to sustain about 108 turn over cycles corresponding to about 20 years of exposure to natural light. Much of the research in dye chemistry is devoted to the identification and synthesis of dyes matching these requirements, while retaining stability in the photo electrochemical environment. The attachment group of the dye ensures that it spontaneously assembles as a molecular layer upon exposing the oxide film to a dye solution. This molecular dispersion ensures a high probability that, once a photon is absorbed, the excited state of the dye molecule will relax by electron injection to the semiconductor conduction ban. However, the optical absorption of a single monolayer of dye is weak, a fact which originally was cited as ruling out the possibility of high efficiency sensitized devices, as, it was assumed that smooth substrate surfaces would be imperative in order to avoid the recombination loss mechanism associated with rough or polycrystalline structures in solid state . Also used in light harvesting by nano crystalline Tio2 films, the dilemma of light harvesting by • PV addresses the energy problem, which many surface, immobilized molecular absorbers. passionately want to solve.

V. PHOTOVOLTAIC PERFORMANCE STABILITY • By 2050 the world will need ~ 30 TW of power. A photovoltaic device must remain serviceable for 20 years without significant loss of performance. The stability of all the 22

International Journal of Electrical Electronics & Computer Science Engineering Volume 1, Issue 5 (October 2014), ISSN : 2348 2273 Available Online at www.ijeecse.com

• Some think PV could provide 20 % of that. It takes a and it looks like a rod of a 600 diameter and cut the solution panel rated at 5 W, to average 1 W of power through the according to our requirements then the slicing wafer is formed day and year, so we would need 30 TW of PV capacity. as shown in the figure • At $1/W, the industry would take in $30 trillion. Cell Fabrication: The sheet is made of 5 layers in 3 easy steps. An aluminum foil is pressed out for the bottom layer. A • The industry is now well over $40 B/yr thin layer of the element molybdenum is printed onto this foil We would need about 30 TW of PV capacity to provide the layer. Another press is used to cover it with 3 more layers world with 20 % of its 30 TW need in 2050. At 1 $/W, 30 consisting of a semiconducting ink, a P/N junction layer, and a trillion in revenue would be generated electrode conducting layer.

There are many approaches to making PV cells and experts do not agree on which one is the best • The overall global economy has been turbulent for a few years.

• Government policies are constantly changing. After the completion of the of the cell fabrication then module • When an industry based on manufacturing grows faster encapsulation process take place. In this module encapsulation than 40 %/year in spurts, it is hard for the supply chain to take a one aluminium or glass then place a EVA and then kept always provide what is needed. a a solar cells on the EVA finally place a another aluminium plate on the solar cells then the module encapsulation process • The cells are in series; current is passed through device is completed. place a photovoltaic systems on the roof of the house as shown in the figure • The current is limited by the layers that produces the least current. Working of a NANO SOLAR CELLS : • The voltages of the cells add 1. Light passes to the middle semiconducting ink layer, which breaks up the electrons. • The higher band gap must see the light first 2. The molybdenum on the fourth layer acts as an electrode, VI. PROCESS TO MANUFACTURE SILICON and as the end of the circuit. PHOTOVOLTAIC CELL 3. The second layer is a P/N junction, which conducts the Silicon is availability from a silicon industry and next step electrons through to the top layer. goes to the ingot growth in these process the impurities is taken from the silicon material by using silicon dioxide the 4. The top layer conducts the electrons and work as the quality of a silicon can be improve. Then the substances can beginning of the circuit. be heated up its melting point then the seed crystal is deep in to the silicon solution and move the seed crystal to upwards 23

International Journal of Electrical Electronics & Computer Science Engineering Volume 1, Issue 5 (October 2014), ISSN : 2348 2273 Available Online at www.ijeecse.com

X. CONCLUSIONS In view of a globally increasing energy demand, treating climatic changes due to continuously increasing carbon dioxide emissions, as well as the foreseeable scarcity of fossil fuels, the development and provision of sustainable methods

for power generation belong to the most urgent challenges of VII. ADVANTAGES mankind. Massive effort at political and economical evelis required to basically modernize the existing energy system. Costs less to manufacture and only $0.30/watt to produce Growing efficiency and new methods through electricity, versus $3/watt for conventional solar panels, nanotechnological know-how may play a key role for the and $1/watt for coal. Maintenance and installation costs required innovation in the energy sector. Nano technological are lower as well. More versatile and durable than components provide for the more efficient utilization of conventional solar panels can be placed in many more energy reserves and the more economical development of places under more conditions. It’s Better, Faster, and renewable. The dye-sensitized nano crystalline Cheaper than conventional solar panels. electrochemical has become a standard device for the conversion of solar energy into electricity. VIII. DISADVANTAGES Recent developments in the area of sensitizers for these devices have lead to dyes which absorb across the visible 1. Even it’s a less cost as compared to convectional solar spectrum to higher efficiencies. The development of an solid cells but its expensive because we using the sliver metal state heterojunction dye keeps additional potential for interconnecting of the panels. for cost reduction and simplification of the manufacturing of 2. The sliver metal has the low resistance. dye solar cells. When replacing their fossil fuels, not only their function as energy source, but also as energy store has to be IX. APPLICATION taken into account, for instance in the automotive sector. Here, alternatives must be found for the long term storage of energy Can be placed nearly anywhere Rooftops, Cars, Laptops, Cell and its availability at short notice and in an efficient infra Phones, etc. It’s cheap, durable, and soon will be a plentiful structure. The move into hydrogen economy and the increased source of electricity utilization of bio fuels are discussed as solutions for the future, which, however, require considerable investments and technological leaps, inter alia on the basis of nanotechnologies. further challenges of the energy sector are the optimization and integration of mobile energy supply systems for the operations of wireless electronic devices, tools and sensors, which have become a key factor in modern industrial society.

XI. REFERENCES

[1] Aldus, Scott. “How Solar Cells Work.” How Stuff Works. 22May2005.

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International Journal of Electrical Electronics & Computer Science Engineering Volume 1, Issue 5 (October 2014), ISSN : 2348 2273 Available Online at www.ijeecse.com

[2] Paul Preuss. “An unexpected discovery could yield a full spectrum solar cell.” Research News. Berkeley Lab. 18

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[3] Sanders, Bob. “Cheap, Plastic Solar Cells May Be on The Horizon.”UC Berkeley Campus News. 28 March 2002. [4] Wang Z S, Yamaguchi T, Sugihara H and Arakawa H 2005 Langmuir 21 4272.

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International Journal of Electrical Electronics & Computer Science Engineering Volume 1, Issue 5 (October 2014), ISSN : 2348 2273 Available Online at www.ijeecse.com

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