Solar Cell and Solar Energy Materials

solar Cell and Solar Energy MaterialsIntroduction One of the biggest challenges to mankind is highly depended on the decrease fusil fuels such as oil, coal, natural gas. Fusil fuels atomic number 18 nonrenewable goose egg choice which usually takes million of years to form. As a result, their reserves argon depleted much faster than it forms. Furthermore, the combustion of these fuels causes environmental degradation d unity air pollution and global warming. Combustion of cytosine-based fossil fuels creates not thus far air pollutants, for example, sulfur oxides, nitrogen odixe and heavy metals, but withal carbon di-oxide, the notorious greenhouse gas widely considered to be the number one culprit of global climate change.1 In order to protect our environment and provide cipher security, nada generated from renewable sources has been extensively studied.2 Though it pass on take some decades to come close to a truly sustainable energy system, the research is being conduct ed to find solutions to (1) increase readiness in production, transmission, and utilization of the remaining fossil fuels, (2) reduce negative impacts to the environment, and (3) develop or improve technologies and infrastructure for the smooth transition to the alternative/ renewable energy sources (e.g., nuclear power, solar energy, wind power, geothermal energy, biomass and biofuels, and hydropower).3 Among those, solar energy has umpteen advantages such as availability and belittleder cost. The search and synthesis for low cost solar cell worldlys make of earth abundant elements has been a topic of extensive study across the globe.A brief historic backgroundIn 1839,the p gamyovoltaic effect was disc all overed by cut physicist, Alexandre-Edmond Becquerel. He constructed the worlds first photovoltaic cell in his fathers lab at age nineteen, which was the beginning of solar energy materials engineering. This experiment was done by illuminating deuce electrodes, which were co ated by light sensitive conductive materials, with different types of light. He observed that electricity increases with the increase of light intensity. accordingly an English galvanic engineer, Willoughby Smith, was discovered the photo conductivity of southeast in 1873. In 1883,Charles Fritts built the first true solar cells made from selenium wafer which is coated with a thin horizontal surface of gold. He found that the capacity was only about 1%. In 1905, Albert Einstein published in a paper that light consists of packets or quanta of energy, which can be change only with its frequency.4 This theory was very simple, but revolutionary that explained the data of photoelectrical effect. The photoelectric effect was experimentally proved by an American experimental physicist, Robert Andrews Millikan, who later won the Nobel Prize for the photoelectric effect and measurement of the foreign mission of the negatron. In 1954, a single-crystal cell of germanium and a cadmium sulphide p-n junction was developed with an energy of 6%. Later the University of Delaw atomic number 18 found that the efficiency exceeds 10% with the first thin bourgeon solar cell which was made of copper sulfide and cadmium sulfide in 1980. In 2007,they achieved 42.8% efficiency in solar cell technology.5 To date, the highest 44.8% efficiencies buzz off been achieved by using multiplex junction solar cells.Solar cellSolar cell is electrical device which converts solar radiation into electricity by photoelectric effect. It consists of two types of semiconducting materials, one is n-type and another is p-type. When these two types of materials placed with each other, it forms depletion form at middle of these two materials. When sun light falls on the depletion layer the materials absorb photon and the negatron from filled valency ring excites to the meet conduction band, which creates a hole and electron pair. The hole goes to the p-type conductor and the electron goes to the n-type conductor. If we complete the circuit by connecting these two materials we will see at that place is flow of electricity. 6Fig 1 A schematic diagram of solar cellSome important Solar cell and solar energy materialsSolar cells atomic number 18 typically consists of semiconducting materials and these cells argon named after thesemiconducting materialsthey atomic number 18 made of. Thesematerialsmust have certain characteristics in order to absorbsunlight. Some solar cells are designed to absorb sunlight that reaches the Earths surface, while others are constructed foruse in space. Solar cells can be made of only one layer of light absorbing semiconducting material which is called single-junction. Sometimes cells can be made of multiple layers of semiconducting materials to take advantage of wide ply of absorption and charge separation mechanisms which is called multi-junction.Solar cells can be categorize into three categories according to multiplicationThe first ge neration cells too called traditional, stately orwafer based cells that are made ofcrystalline te which includes materials such asmono-crystalline and poly-silicon silicon.Second generation cells arethin consider solar cells, that includeamorphous silicon,CdTeandCIGScells and are commercially significant in utility-scale photovoltaic power stations,building integrated photovoltaicsor in smallstand alone devices.The third generation of solar cells includes a number of thin-film technologies often described as emerging photovoltaics which are not yet commercially applied and are still in the research or development phase such as perovskite solar cells and quantum dots solar cells.Crystalline siliconThe virtually prevalent bulk material for solar cells iscrystalline silicon(c-Si), also known as solar grade silicon. lot silicon is separated into two categories according to crystallinity and crystal size.Mono-crystalline silicon crystalline siliconIn 1981, the first solar panels ba sed on crystalline silicon, which also is known as polysilicon (p-Si) and multi-crystalline silicon (mc-Si),was introduced to the market. Unlike monocrystalline-based solar panels, polycrystalline solar panels do not require the Czochralski process. Raw silicon is liquefied and poured into a square mold, which is cooled and cut into perfectly square wafers. Polysilicon cells are the most common type used in photovoltaics and are less expensive, yet less efficient than those made from monocrystalline silicon.Thin filmThin film technologies reduce the amount of active material in a cell. just about designs sandwich active material between two panes of glass. Since silicon solar panels only use one pane of glass, thin film panels are approximately twice as heavy as crystalline silicon panels, although they have a smaller ecological impact.8The majority of film panels have 2-3 percentage points swallow conversion efficiencies than crystalline silicon. Cadmium telluride(CdTe),copper indium tabun selenide(CIGS) andamorphous silicon(a-Si) are three thin-film technologies often used for outdoor applications. CIGS technology laboratory demonstrations reached 20.4% as of December 2013. The lab efficiency of GaAs thin film technology topped 28%. Thequantum efficiencyof thin film solar cells is also lower due to reduced number of collected charge carriers per incident photon. more or less recently, CZTS solar cell emerge as the less-toxic thin film solar cell technology, which achieved 12% efficiency.Cadmium tellurideCadmium telluride is the only thin film material so far to rival crystalline silicon in cost/watt. However cadmium is a highly toxic andtelluriumsupplies are limited. Thecadmiumpresent in the cells would be toxic if released. However, release is impossible during normal execution of the cells and is unlikely during fires in residential roofs.9A square meter of CdTe contains approximately the same amount of Cd as a single C cellnickel-cadmium battery, in a more stable and less soluble form.9Copper indium gallium selenideCopper indium gallium selenide (CIGS) is adirect band gapmaterial. It has the highest efficiency (20%) among all commercially significant thin film materials. Traditional methods of fabrication involve vacuum processes including co-evaporation and sputtering. Recent developments atIBMandNanosolar attempt to lower the cost by using non-vacuum solution processes.Gallium arsenide thin filmThe semiconductor unit materialGallium arsenide(GaAs) is also used for single-crystalline thin film solar cells. Although GaAs cells are very expensive, they build the worlds record in efficiency for asingle-junctionsolar cell at 28.8%.10GaAs is more ordinarily used inmultijunction photovoltaic cellsforconcentrated photovoltaics and forsolar panels on spacecrafts, as the industry favours efficiency over cost forspace-based solar power.Perovskite solar cellsThe name perovskite solar cell is derived from the ABX3crystal structureof the absorber materials, which is referred to as perovskite structure. The most commonly studied perovskite absorber is methylammonium lead trihalide (CH3NH3PbX3, where X is ahalogenion such asI,Br,Cl). Formamidinumlead trihalide (H2NCH3NH3PbX3) is a recently studied newer material which shows promise, with a bandgap between 2.23eV and 1.48eV. This minimum bandgap is circumferent to the optimal for asingle-junction cellthan methylammonium lead trihalide, so it should be capable of higher efficiencies. The efficiencies of perovskite solar cell have increased to 12.8% in 2014.11 This increased efficiency is reservation them a very rapidly advancing technology and a hot topic in the solar cell field. Perovskite solar cells are also forecast to be extremely cheap to scale up, making them a very attractive option for commercialization.Quantum dots semiconductor solar cellQuantum dots are tiny particles or nanocrystals of a semiconducting material with diameters in the black market of 2-10 nanometers. Due to high surface to volume ratios for these particles, quantum dots display unique electronic properties, intermediate between those of bulk semiconductors and discrete molecules. Due to their small size, the electrons in quantum dots are confined in a small space which is called quantum box. When the radii of the semiconductor nanocrystal is smaller than the exciton Bohr radius (exciton Bohr radius is the average distance between the electron in the conduction band and the hole it leaves behind in the valence band), there is quantization of the energy levels according to Paulis exclusion convention (Figure 1).1213The discrete, quantized energy levels of quantum dots relate them more closely to atoms than bulk materials. Generally, as the size of the crystal decreases, the difference in energy between the highest valence band and the lowest conduction band increases. More energy or more energy light is then needed to excite an electron from valance band to cond uction band. Therefore, the properties of semiconducting materials can be tuned by changing the size of the quantum dots. By using different sized quantum dots in multi-layer junction we can absorb wide range of light.Figure 4 Splitting of energy levels in quantum dots due to the quantum confinement effect, semiconductor band gap increases with decrease in size of the nanocrystal.1213ConclusionThe primary energy sources coal, oil and natural gas are fossil fuels are polluting our environment. Furthermore, these resources are quickly depleting and becoming extremely expensive day by day. Therefore, weneedtoconsiderrenewableenergysources such as solar energy, by using solar cells we cangenerate electricalpower by converting solar energy intoelectricity.ReferenceWang, Zhong Lin.Nanotechnology for the energy challenge. Ed. Javier Garca-Martnez. John Wiley Sons, 2013.Hou, Yu, Ruxandra Vidu, and Pieter Stroeve. Solar energy reposition methods.Industrial Engineering Chemistry Research50 .15 (2011) 8954-8964.Moniz, E. J. Garcia-Martinez, J. 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