Thin Film Solar Cell
Abstract: Solar energy is quite simply the energy produced directly from the sun and collected elsewhere, namely the Earth. Photovoltaic technology directly converts solar energy into electricity. Photovoltaic thin film solar cells are easy to handle , inexpensive and also easy to use. Thin film panel is flexible and can tolerate a bullet hole without failing and can greatly increase the surface area and the absorption coefficient needed to generate electricity. This paper will discuss the advantages and disadvantages of the thin- film solar cell and also describe its application and how its work.
Introduction: The solar cell is the latest technology around the world. The solar cell is also called a renewable energy source, because the capture the sunlight and convert it into the electrical energy. There are different types of solar cells, but the most important one is a thin- film solar cell. It is cost effective and its efficiency is greater than the other types of solar cells like thin film dye sanitized solar cell . Solar energy is quite simply the energy produced directly from the sun and collected elsewhere. All solar cells are made of silicon.
Thin- Film Photovoltaic technology directly converts solar energy into electricity. Solar cells are made out of semiconducting material, usually silicon. The process of making a solar cell begins with taking a slice of highly purified silicon crystal, and then processing it through several stages involving gradual heating and cooling. Solar cells are based on semiconductor physics — they are essentially just a P-N junction photo-diodes with a very large light-sensitive area. Another common material for thin- film cells include Gallium Aarsenide (GaAs), Copper Indium Gallium Selenide, and gallium Phosphide.
The most common types of photovoltaic cells are single-junction, multi-junction, and thin-film. A thin film panel is flexible and can tolerate a bullet hole without failing and can greatly increase the surface area and the absorption coefficient needed to generate electricity. Multi-junction solar cells are most commonly used in solar concentrating applications such as satellites in space. Today we use solar power to do many things. We use solar power for everything from calculators to large power plants that can power large cities. The most common applications for solar panels are used for small evices. The Solar cell technology research is continuing to create low-cost high-efficiency elements and the latest approaches in solar cell designs. Some countries do not have oil or do not have enough political and economic power to buy it or to produce it, but they receive more sunlight than others. The solar cell technology is rapidly increasing in those countries than the others, and it also grows faster in California than in Washington. Polycrystalline thin-film solar cells are based on those compounds which have the efficiencies up to 19. 2%. Nowadays, it is increased by 20. 4%.
The Swiss Federal Laboratories for Material Science and Technology has recently developed a new thin-film solar cell with an efficiency of 20. 4%. Those cells are based on CIGS (copper indium gallium (DI) selenide) semiconductor material. The band gap on the top of the solar cell around 1. 6-1. 8 EV. The thin-film solar cells should be design by single-junction and also two- junction devices commonly used CIGS and CdZnTe. There are four different types of thin-film solar cell. 1. Amorphous silicon (a-Si) 2. Cadmium telluride (CdTe) 3. Copper indium gallium selenide (CIS/CIGS) 4. Organic photovoltaic cells (OPC) How Thin-Film Solar Cell Works:
Thin-film solar cells are also called new generation of solar cell. This cell contains multiple layers of PV material. This new generation solar cells produce over 3700 megawatts of electrical energy in 2010. The main difference between the structure of normal silicon solar cells and thin film silicon solar cell is the thin flexible arrangement of the different layer as is shown as figure (1). The only advantage of that layer is to create a greater surface area for sunlight absorption and also it is very low weight and easy to use in cars and small devices. Figure (1) We use calculator everyday in our normal daily routine.
These solar powered calculators have a small solar cell at the top corner of the calculator. These cells are built with thin –film technology. Most of them are very small about an inch long and ? inch wide. The thin-film solar cells are very thin that’s why they Called thin-film solar cell. Thin-film solar cell is different than the silicon wafer. Silicon wafer and thin-film solar cell have a light absorbing layer, but only difference is the thickness. The silicon wafer has 350 microns thick,but the thin-film solar cell has only one micron, and as result thin-film solar cell is very light weight compared to other solar cells.
Thin-film solar cells are made of several layers. Those all layer helps to absorb light. As you can see in the figure (2). (Different layers in thin-film solar cell) Figure (2) On the other hand, some thin-film solar cell required the three functional layers from the multiple layers in a solar cell. These three have different important function. In the figure (a), show the front contact and back contact layers which have only one job to do and that’s is to provide the electrical contact with the solar cell from the outside the world. The figure (a) shows the basic theory of the different layer stack of the thin-film solar cell.
Thin -film solar cell implemented by the different ways , but the three most common inorganic technologies are CuSe2 , CdTe solar cell, and also thin-film solar cell which has an amorphous and microcrystalline silicon absorber. There are three major types of thin-film solar cell. 1. Amorphous silicon (a-Si) 2. Cadmium Telluride (CdTe) 3. Copper indium gallium deselenide (CIGS). The (a-Si) solar cell is very commonly used and also easy to understand and implement it, but there are two major problems that cause this type of solar cell to have some drawbacks.
The first problem is, silicon is very hard to find the market and buy it , because its demand often exceeds the supply. The second thing is, this type of solar cell has very low efficiency. This type of solar cell is also very thinner so they absorb sunlight in very less and on the other hand, they do not have enough power to absorb more. Therefore, they used in calculator and other very small and low power consuming devices. The Advantages of Thin-Film Solar Cell:
1. Thin-film solar cell is very cheaper than the silicon solar cell
2. They are also available in thin wafer sheet.
3.More flexible and very easy to handle it.
4. Less thinner than crystalline solar cell. It can be as thin . 001 mm or more, but the crystalline solar cells are . 15-. 2 mm thick.
5. Easy to install on the rooftop with a rugged mounting system with tilt at a fixed degree.
6. Thin film solar cells have better performance in the hot weather. See table (1) below.
Table (1) | The efficiency of solar panel /%| Temperature /degree| a-Si thin film| Crystalline| 25 (STC)| 10| 16| 35| 8| 11| 45| 6| 6| 50| 5| 3. 5| The Disadvantages of Thin-Film Solar Cell: 1. Less efficient than the normal standard silicon and crystalline solar cell.
See table (2) below. Table (2) Condition| Crystalline Efficiency Drop| Light San Francisco fog| 8%-15%| Heavy San Francisco fog| 15%-20%| Cloudy & raining| 20% – 50%| Heavy cloudy & raining| 50% – 90%| 2. They have complex structure. 3. Different version requires its own unique installation skills. 4. They are also not available for aerospace applications. 5. They faster to degrade than the other solar cells that’s why they always come with a shorter warranty. 6. They require a huge space so they are not good for most residential situations. Applications Of Thin-Film solar cell:
Thin-film solar cell panels are used in many power applications. They are also used for outdoor and energy generating applications. These cells are very light weight and easy to use in homes and small business. They can be installed on the rooftops of the most homes. They use calculators, cars and other portable electronics. They are also used in cloths also enables the powering the iPod, iPad, and cell phones during the hiking. Thin film solar cells are used in mobile charger and led lights. Conclusion: The advancement of Photovoltaic thin film solar cell is increasing rapidly.
The development and decisions on materials used in PV thin film solar cell are crucial when trying to achieve optimal performance for a good price. The discovery of the photoelectric effect and the concept of photons sparked interest of finding more ways to create efficient PV cells. The decisions on what materials to use in PV cells have paved the way for new developments and increased efficiency. When the first thin film solar cell was created it was around 1% efficient and with today’s innovations and engineering decisions efficiencies are now able to achieve up to 20. %. If this trend to improvement continues the way it has been over the past 40 years then the technology may pave the way for complete solar power generations . References: 1. Harris, William. “How Thin-film Solar Cells Work” 07 April 2008. HowStuffWorks. com. <http://science. howstuffworks. com/environmental/green-science/thin-film-solar-cell. htm> [22 march 2013]. 2. Mathias Aarre M? hlum. “Which Solar Panel Types is Best” Internet: http://energyinformative. org/best-solar-panel-monocrystalline-polycrystalline