INFRARED PLASTIC SOLAR CELL
-A product of nanotechnology
Nanotechnology is the nexus of sciences. Nanotechnology is the engineering of tiny machines - the projected ability to build things from the bottom up using techniques and tools being developed today to make complete, highly advanced products. It includes anything smaller than 100 nanometers with novel properties. As the pool of available resources is being exhausted, the demand for resources that are everlasting and eco-friendly is increasing day by day. One such form is the solar energy. The advent of solar energy just about
solved all the problems. As such solar energy is very useful. But the conventional solar cells that are used to harness solar energy are less efficient and cannot function properly on a cloudy day. The use of nanotechnology in the solar cells created an opportunity to overcome this problem, thereby increasing the efficiency. This paper deals with an offshoot in the advancement of nanotechnology, its implementation in solar cells and its advantage over the conventional commercial solar cell.
WHAT IS NANOTECHNOLOGY?
The pursuit of nanotechnology comprises a wide variety of disciplines: chemistry, physics, mechanical engineering, materials science, molecular biology, and computer science.
In order to the miniaturization of integrated circuits well into the present century, it is likely that present day, nano-scale or nanoelectronic device designs will be replaced with new designs for devices that take advantage of the quantum mechanical effects that dominate on the much smaller,nanometer scale.
Nanotechnology is often referred to as general purpose technology. That is because in its mature form it will have
significant impact on almost all industries and all areas of society. It offers better built, longer lasting, cleaner, safer and smarter products for the home, for ammunition, for medicine and for industries for ages. These properties of nanotechnology have been made use of in solar cells. Solar energy is really an abundant source that is renewable and pollution free. This form of energy has very wide applications ranging from small household items, calculators to larger things like two wheelers, cars etc. they make use of solar cell that coverts the energy from the sun into required form.
1. WORKING OF CONVENTIONAL SOLAR CELL: Basically conventional type solar cells Photovoltaic (PV) cells are made of special materials called semiconductors such as silicon, which is currently the most commonly used. Basically, when light strikes the cell, a certain portion of it is absorbed within the semiconductor material. This means that the energy of the absorbed light is transferred to the semiconductor. The energy knocks electrons loose, allowing them to flow freely. PV cells also all have one or more electric fields that act to force electrons freed by light absorption to flow in a certain direction. This flow of electrons is a current, and by placing metal contacts on the top and bottom of the PV cell, we can draw that current off to use externally. For example, the current can power a calculator. This current, together with the cell's voltage (which is a result of its built-in electric field or fields), defines the power (or wattage) that the solar cell can produce. Conventional semiconductor solar cells are made by polycrystalline silicon or in the case of highest efficiency ones crystalline gallium arsenide.
But by this type of solar cell, it is observed that, only 35% of the suns total energy falling on it could be judiciously used. Also, this is not so favorable on cloudy days, thus creating a problem. This major draw back led to the thought of development of a new type of solar cell embedded with nanotechnology. The process involved in this is almost the same as explained earlier. But the basic difference lies in the absorption of the wavelength of light from the sun.
Various developments regarding this field are explained below:
2. INFRARED plastic solar cell:
Scientists have invented a plastic solar cell that can turn the suns power into electric energy even on a cloudy day. Plastic solar cells are not new. But existing materials are only able to harness the sun’s visible light. While half of the sun’s power lies in the visible spectrum, the other half lies in the infrared spectrum. The new material is first plastic compound that is able to harness infrared portion. Every warm body emits heat. This heat is emitted even by man and by animals, even when it is dark outside. The plastic material uses nanotechnology and contains the 1stgeneration solar cells that can harness the sun’s invisible infrared rays. This breakthrough made us to believe that plastic solar cells could one day become more efficient than the current solar cell. The researchers combined specially designed nano particles called quantum dots with a polymer to make the plastic that can detect energy in the infrared.
With further advances the new plastic solar cell could allow up to 30% of sun’s radiant energy to be harnessed completely when compared WHEN COMPAWHEN COMPARED to only 6% in today plastic best plastic solar cells.
A large amount of sun’s energy could be harnessed through solar farms and used to power all our energy needs. This could potentially displace other source of electrical production that produce green house gases like coal.
Solar energy reaching the earth is 10000 times than what we consume. If we could cover .1% of the earth’s surface with the solar farms we could replace all our energy habits with a source of power which is clear and renewable.
The first crude solar cells have achieved efficiencies of today’s standard commercial photovoltaics the best solar cell, which are very expensive semiconductor laminates convert at most, 35% of the sun’s energy into electricity.
2.1. WORKING OF PLASTIC SOLAR CELL:
The solar cell created is actually a hybrid, comprised of tiny nanorods dispersed in an organic polymer or plastic. A layer only 200 nanometers thick is sandwiched between electrodes and can produce at present about .7 volts. The electrode layers and nanorod /polymer layers could be applied in separate coats, making production fairly easy. And unlike today’s semiconductor-based photovoltaic devices, plastic solar cells can be manufactured in solution in a beaker without the need for clean rooms or vacuum chambers.
The technology takes advantage of recent advances in nanotechnology specifically the production of nanocrystals and nanorods. These are chemically pure clusters of 100 to 100000 atoms with dimensions of the order of a nanometer, or a billionth of a meter. Because of their small size, they exhibit unusual and interesting properties governed by quantum mechanics, such as the absorption of different colors of light depending upon their size. Nanorods were made of a reliable size out of cadmium selenide, a semi conducting material.
Nanorods are manufactured in a beaker containing cadmium selenide, aiming for rods of diameter-7 nanometers to absorb as much sunlight as possible. The length of the nanorods may be approximately 60nanometers.Then the nanorods are mixed with a plastic semiconductor called p3ht-poly-(3-hexylthiophene) a transparent electrode is coated with the mixture. The thickness, 200 nanometers-a thousandth the thickness of a human hair-is a factor of 10 less than the micron-thickness of semiconductor solar cells. An aluminium coating acting as the back electrode completed the device. The nanorods act like wires. When they absorb light of a specific wavelength, they generate an electron plus an electron hole-a vacancy in the crystal that moves around just like an electron. The electron travels the length of the rod until it is collected by aluminium electrode. The hole is transferred to the plastic, which is known as a hole-carrier, and conveyed to the electrode, creating a current.
Some of the obvious improvements include better light collection and concentration, which already are employed in commercial solar cells. Significant improvements can be made in the plastic, nanorods mix, too, ideally packing the nanorods closer together, perpendicular to the electrodes, using minimal polymer, or even none-the nanorods would transfer their electrons more directly to the electrode. In their first-generation solar cells, the nanorods are jumbled up in the polymer, leading to losses of current via electron-hole recombination and thus lower efficiency.
They also hope to tune the nanorods to absorb different colors to span the spectrum of sunlight. An eventual solar cell has three layers each made of nanorods that absorb at different wavelength.
· Silicon possesses some nanoscale properties. This is being exploited in the development of a super thin disposable solar panel poster which could offer the rural dwellers a cheap and an alternative source of power. Most people living in remote areas are not linked to national electricity grid and use batteries or run their own generator to supply their power needs. Disposal solar panels can be made in thin sheets with about 6-10 sheets stacked together and made into a poster can help them to some extent in this regard. This poster could be mounted behind a window or attached to a cabinet.
· Like paint the compound can also be sprayed onto other materials and used as portable electricity.
· Any chip coated in the material could power cell phone or other wireless devices.
· A hydrogen powered car painted with the film could potentially convert energy into electricity to continually recharge the car’s battery.
· One day solar farms consisting of plastic materials could be rolled across deserts to generate enough clear energy to supply the entire planet’s power needs.
Plastic solar cells are quite a lot useful in the coming future. This is because of the large number of advantages it has got. Some of the major advantages are:
· They are considered to be 30% more efficient when compared to conventional solar cells.
· They are more efficient and more practical in application.
· Traditional solar cells are bulky panels. This is very compact.
· Conventional solar cells are only used for large applications with big budgets. But the plastic solar cells are feasible as they can be even sewn into fabric- thus having vast applications.
· Flexible, roller processed solar cells have the potential to turn the sun’s power into a clean, green, consistent source of energy.
· The biggest problem with this is cost effectiveness. But that could change with new material. But chemists have found a way to make cheap plastic solar cells flexible enough to paint onto any surface and potentially able to provide electricity for wearable electronics or other low power devices.
· Relatively shorter life span when continuously exposed to sunlight.
· Could possibly require higher maintenance and constant monitoring.
Plastic solar cells help in exploiting the infrared radiation from the suns rays. They are more effective when compared to the conventional solar cell. The major advantage they enjoy is that they can even work on cloudy days, which is not possible in the former. They are more compact and less bulkier.
Though at present, cost is a major draw back, it is bound be solved in the
1. Nanomaterials: Synthesis, Properties and Applications: Edelstein, A. S., Cammarata, R. C., Eds.; Institute of Physics Publishing: Bristol and Philadelphia, 1996.near future as scientists are working in that direction.
As explained earlier, if the solar farms can become a reality, it could possibly solve the planets problem of depending too much on the fossil fuels, without a chance of even polluting the environment.
2. Solar energy-fundamentals, design, modeling, applications- G.N. Tiwari
3. Thin film solar cells next generation photovoltaics and its application- y Hamakawa