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  Cross-section of thin film polycrystalline solar cell. Possible combinations of Group-(I, III, VI)elements in the periodic table that yield a compound showing photovoltaic effect( Cu, Ag, Au | Al, Ga, In | S, Se, Te ). Thin film solar cell From Wikipedia, the free encyclopedia  (Redirected from Silicon thin-film cell)A thin-film solar cell  (TFSC), also called a thin-filmphotovoltaic cell  (TFPV), is a solar cell that is made bydepositing one or more thin layers (thin film) of photovoltaicmaterial on a substrate. The thickness range of such a layer is wide and varies from a few nanometers to tens of micrometers.Many different photovoltaic materials are deposited withvarious deposition methods on a variety of substrates. Thin-film solar cells are usually categorized according to the photovoltaic material used:Amorphous silicon (a-Si) and other thin-filmsilicon (TF-Si)Cadmium Telluride (CdTe)Copper indium gallium selenide (CIS or CIGS)Dye-sensitized solar cell (DSC) and other organic solar cells Contents 1 History2 Thin-film silicon2.1 Design and fabrication2.2 Micromorphous silicon2.3 Efficiency2.4 Building integrated photovoltaics3 Organic solar cells4 Efficiencies, volumes and prices5 Production, cost and market6 Installations7 Time Award 8 See also9 References10 Sources11 External links History Initially appearing as small strips powering hand-held calculators, thin-film PV is now available in very large  modules used in sophisticated building-integrated installations and vehicle charging systems. GBI Research projectsthin film production to grow 24% from 2009 levels and to reach 22,214 MW in 2020. Expectations are that in thelong-term, thin-film solar PV technology would surpass dominating conventional solar PV technology, thus enablingthe long sought-after grid parity objective. [1][2] Thin-film silicon A silicon thin-film cell uses amorphous (a-Si or a-Si:H), protocrystalline, nanocrystalline (nc-Si or nc-Si:H) or black silicon. Thin-film silicon is opposed to wafer   (or bulk  ) silicon (monocrystalline or polycrystalline). Design and fabrication The silicon is mainly deposited by chemical vapor deposition, typically plasma-enhanced (PE-CVD), from silanegas and hydrogen gas. Other deposition techniques being investigated include sputtering and hot wire techniques.The silicon is deposited on glass, plastic or metal which has been coated with a layer of transparent conductingoxide (TCO).A p-i-n structure is usually used, as opposed to an n-i-p structure. This is because the mobility of electrons in a-Si:H is roughly 1 or 2 orders of magnitude larger than that of holes, and thus the collection rate of electrons movingfrom the p- to n-type contact is better than holes moving from p- to n-type contact. Therefore, the p-type layer should be placed at the top where the light intensity is stronger, so that the majority of the charge carriers crossingthe junction would be electrons. [3] Micromorphous silicon Micromorphous silicon module technology combines two different types of silicon, amorphous and microcrystalline,in a top and a bottom photovoltaic cell. These two materials are chosen because their different absorptionspectrums and easily combined process. Because the two different materials are both Si, they can be manufactured in the same technology, which now is PECVD. The band gap of a-Si is 1.7 eV and that of c-Si is 1.1 eV, whicheventually broaden the spectral acceptance of the micromorph tandem solar cell. The The c-Si layer can help toabsorb the energy of red and infrared spectrum and increase the overall efficiency. The best efficiency can beachieved at transition between a-Si and c-Si. Use of protocrystalline silicon for the intrinsic layer has shown tooptimize the open-circuit voltage of an a-Si photovoltaic cell. [4] Efficiency These types of silicon present dangling and twisted bonds, which results in deep defects (energy levels in the bandgap) as well as deformation of the valence and conduction bands (band tails). The solar cells made from thesematerials tend to have lower energy conversion efficiency than bulk silicon (also called crystalline or wafer silicon), but are also less expensive to produce. The quantum efficiency of thin-film solar cells is also lower due to reduced number of collected charge carriers per incident photon.Amorphous silicon has a higher bandgap (1.7 eV) than crystalline silicon (c-Si, 1.1 eV), which means it absorbs thevisible part of the solar spectrum more strongly than the infrared portion of the spectrum. As nc-Si has about thesame bandgap as c-Si, the nc-Si and a-Si can advantageously be combined in thin layers, creating a layered cellcalled a tandem cell . The top cell in a-Si absorbs the visible light and leaves the infrared part of the spectrum for   Solar cell efficienciesThin film photovoltaic panels beinginstalled onto a roof  the bottom cell in nc-Si.Recently, solutions to overcomethe limitations of thin-film siliconhave been developed. Lighttrapping schemes where theincoming light is obliquely coupled into the silicon and the lighttraverses the film several timesenhance the absorption of sunlightin the films. Thermal processingtechniques enhance the crystallinityof the silicon and pacify electronicdefects. [ citation needed  ] Building integratedphotovoltaics Thin film solar panels arecommercially available for installation onto the roofs of buildings, either applied onto the finished roof, or integrated into the roof covering. Theadvantage over tradition PV panels is that they are very low in weight,are not subject to wind lifting, and can be walked on (with care). Thecomparable disadvantages are increased cost and reduced efficiency.A silicon thin film technology is being developed for building integrated  photovoltaics (BIPV) in the form of semitransparent solar cells which can be applied as window glazing. These cells function as window tintingwhile generating electricity. Organic solar cells The organic solar cell is another alternative to the more conventional materials used to make photovoltaics.Although a very novel technology it is promising since it offers a very low cost solution. Efficiencies, volumes and prices Since the invention of the first modern silicon solar cell in 1954, incremental improvements have resulted in modulescapable of converting 12 to 18 percent of solar radiation into electricity. [5]  The performance and potential of thin-film materials are high, reaching cell efficiencies of 12–20%; prototype module efficiencies of 7–13%; and  production modules in the range of 9%. Future module efficiencies are expected to climb close to the state-of-the-art of today's best cells, or to about 10–16%. [6] Annual manufacturing volume in the United States has grown from about 12 megawatts (MW) per year in 2003 tomore than 20 MW/yr in 2004; 40–50 MW/yr production levels are expected in 2005 with continued rapid growthin the years after that.  Costs are expected to drop to below $100/m 2  in volume production, and could reach even lower levels—wellunder $50/m 2 , the DOE/NREL goal for thin films—when fully optimized. At these levels, thin-film modules will costless than fifty cents per watt to manufacture, opening new markets such as cost-effective distributed power and utility production to thin-film electricity generation. [7] As crystalline silicon price rose, the production cost of silicon-based solar cell module in 2008 was at some point4–5 times higher than that of thin film modules. Thin-film producers still enjoy in 2009 price advantage as its production cost is 20% less than that of silicon modules.It is expected that the production cost of thin-film willcontinue dropping (40% less than silicon), as Chinese producers are now putting more resources into R&D and  partnering with manufacturing equipment suppliers [8] Production, cost and market In recent years, the manufacturers of thin-film solar modules are bringing costs down and gaining in competitivestrength through advanced thin film technology. However, the traditional crystalline silicon technologies will not giveup their market positions for a few years because they still hold considerable development potential in terms of thecost. Efficiency of thin film solar is considerably lower and thin film solar manufacturing equipment suppliers intend to score costs of below USD 1/W, and Anwell Technologies Limited claimed that they intend to bring it downfurther to USD 0.5/W. [9]  Those equipment suppliers have been doing R&D for micro-morphous silicon modulessince 2008. This technology represents a development based on the thin-film panels made of ordinary amorphoussilicon marketed at present that brings higher cell efficiency by depositing an additional absorber layer made of micro crystalline silicon on the amorphous layer. Some equipment suppliers even claim that there will be machineryin market to manufacture these new modules at $0.70. [10]  With such potential of further development of thin filmsolar technology, the European Photovoltaic Industry Association (EPIA) expects that manufacturing capacities for these technologies will double to over 4GW by 2010 representing a market share of around 20%. [11] GE announced plans to spend $600 million on a new CdTe solar cell plant and enter this market [12] Installations First Solar, the CdTe thin-film manufacturer stated that at the end of 2007, over 300 MW of First Solar PVmodules had been installed worldwide. Below is a list of several recent installations: [6] Since 16 October 2008, Germany's largest thin-film pitched roof system, constructed by RiedelRecycling, has been in operation and producing solar power in Moers near Duisburg. Over eleventhousand cadmium telluride modules, from First Solar, deliver a total of 837 kW. [13] First Solar recently completed a 2.4 MW rooftop installation as part of Southern California Edison program to install 250 MW of rooftop solar panels throughout Southern California over by 2013. [14] First Solar announced a 7.5 MW system to be installed in Blythe, CA, where the California PublicUtilities Commission has accepted a 12 ¢/kWh power purchase agreement with First Solar (after theapplication of all incentives). [15] Construction of a 10 MW plant in the Nevada desert began in July 2008. [16][17]  First Solar is partneringwith Sempra Generation, which will own and operate the PV power-plant, being built next to their natural gas plant.Stadtwerke Trier (SWT) in Trier, Germany is expected to produce over 9 GWh annuallyA 40 MW system is being installed by Juwi in Waldpolenz Solar Park, Germany. At the time of its
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