Solar Cell and Solar Energy Materials

Solar Cell and Solar Energy Materials Introduction: One of the biggest challenges to mankind is highly depended on the decreasing fusil fuels such as oil, coal, natural gas. Fusil fuels are nonrenewable energy resource which usually takes million of years to form. As a result, their reserves are depleted much faster than it forms. Furthermore, the combustion of these fuels causes environmental degradation through air pollution and global warming. Combustion of carbon-based fossil fuels creates not only air pollutants, for example, sulfur oxides, nitrogen odixe and heavy metals, but also 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 energy security, energy generated from renewable sources has been extensively studied.[2] Though it will take some decades to come close to a truly sustainable energy system, the research is being conducted to find solutions to (1) increase efficiency in production, transmission, and u tilization 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 many advantages such as availability and lower cost. The search and synthesis for low cost solar cell materials made of earth abundant elements has been a topic of extensive study across the globe. A brief historical background: In 1839,the photovoltaic effect was discovered by French physicist, Alexandre-Edmond Becquerel. He constructed the worlds first photovoltaic cell in his fathers laboratory at age nineteen, which was the beginning of solar energy materials technology. This experiment was done by illuminating two electrodes, which were coated by light sensitive semiconducting materials, with different types of light. He observed that electricity increases with the increase of light intensity. Then an English electrical engineer, Willoughby Smith, was discovered the photo conductivity of selenium in 1873. In 1883,Charles Fritts built the first true solar cells made from selenium wafer which is coated with a thin layer of gold. He found that the efficiency was only about 1%. In 1905, Albert Einstein published in a paper that light consists of â€Å"packets† or quanta of energy, which can be varied only with its frequency.[4] This theory was very simple, but revolutionary that explained the data of photoelectric 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 charge of the electron. In 1954, a single-crystal cell of germanium and a cadmium sulphide p-n junction was developed with an efficiency of 6%. Later the University of Delaware found that the efficiency exceeds 10% with the first thin film 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 have been achieved by using multiple junction solar cells. Solar cell: Solar 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 layer at middle of these two materials. When sun light falls on the depletion layer the materials absorb photon and the electron from filled valence band excites to the unfilled 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 there is flow of electricity. [6] Fig 1: A schematic diagram of solar cell Some important Solar cell and solar energy materials Solar cells are typically consists of semiconducting materials and these cells are named after thesemiconducting materialsthey are 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 range of absorption and charge separation mechanisms which is called multi-junction. Solar cells can be classified into three categories according to generation: The first generation cells also called traditional, conventional orwafer based cells that are made ofcrystalline silicon which includes materials such asmono-crystalline and poly-silicon silicon. Second generation cells arethin film 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 silicon The most prevalent bulk material for solar cells iscrystalline silicon(c-Si), also known as solar grade silicon. Bulk silicon is separated into two categories according to crystallinity and crystal size. Mono-crystalline silicon Polycrystalline silicon In 1981, the first solar panels based on polycrystalline 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 melted 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 film Thin film technologies reduce the amount of active material in a cell. Most 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.[8]The majority of film panels have 2-3 percentage points lower conversion efficiencies than crystalline silicon. Cadmium telluride(CdTe),copper indium gallium 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. Most recently, CZTS solar cell emerge as the less-toxic thin film solar cell technology, which achieved ~12% efficiency. Cadmium telluride Cadmium 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 operation of the cells and is unlikely during fires in residential roofs.[9]A 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.[9] Copper indium gallium selenide Copper 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 film The semiconductor materialGallium arsenide(GaAs) is also used for single-crystalline thin film solar cells. Although GaAs cells are very expensive, they hold the worlds record in efficiency for asingle-junctionsolar cell at 28.8%.[10]GaAs is more commonly used inmultijunction photovoltaic cellsforconcentrated photovoltaics and forsolar panels on spacecrafts, as the industry favours efficiency over cost forspace-based solar power. Perovskite solar cells The 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 closer 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 making 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 cell: Quantum dots are tiny particles or nanocrystals of a semiconducting material with diameters in the range 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 Pauli’s exclusion principle (Figure 1).[12][13]The 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 conduc tion band increases. More energy or more energy light is then needed to excite an electron from valance band to conduction 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.[12][13] Conclusion The 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. Reference: Wang, Zhong Lin.Nanotechnology for the energy challenge. Ed. Javier Garcà ­a-Martà ­nez. John Wiley Sons, 2013. Hou, Yu, Ruxandra Vidu, and Pieter Stroeve. Solar energy storage methods.Industrial Engineering Chemistry Research50.15 (2011): 8954-8964. Moniz, E. J.; Garcia-Martinez, J. Nanotechnology for the Energy Challenge; Wiley-VCH: Weinheim, Germany, 2010 Einstein, Albert. The photoelectric effect.Ann. Phys17 (1905): 132. Delaware University, US, HP http://www.udel.edu/PR/ UDaily/2008/jul/solar072307 .html Li, Zhongrui, et al. Light-harvesting using high density p-type single wall carbon nanotube/n-type silicon heterojunctions.Acs Nano3.6 (2009): 1407-1414. Green, M. A. Recent developments in photovoltaics.Solar energy76.1 (2004): 3-8. Pearce, Joshua, and Andrew Lau. Net energy analysis for sustainable energy production from silicon based solar cells.ASME Solar 2002: International Solar Energy Conference. American Society of Mechanical Engineers, 2002. Fthenakis, Vasilis M. Life cycle impact analysis of cadmium in CdTe PV production.Renewable and Sustainable Energy Reviews8.4 (2004): 303-334. Yablonovitch, E., O. D. Miller, and S. R. Kurtz. The opto-electronic physics that broke the efficiency limit in solar cells.Photovoltaic Specialists Conference (PVSC), 2012 38th IEEE. IEEE, 2012. Qin, Peng, et al. Perovskite Solar Cells with 12.8% Efficiency by Using Conjugated Quinolizino Acridine Based Hole Transporting Material.Journal of the American Chemical Society(2014). Reimann, S. M.; Manninen, M. Reviews of Modern Physics, 2002, 74(4), 1283. Bawendi, M. C.; Steigerwald, M. L.; Brus, L. E. Annual Review of Physical Chemistry, 1990, 41, 477.

Income Tax Exemptions in Pakistan

In The name Of Allah The Most Merciful & The Most Beneficent Assignment of: Principle & Practice Income Tax Topic: Need of Tax Exemption [pic] Question: What is the need of Tax Exemption or Tax Concession in income tax from government point of view? And Does present income tax exemption policy of Pakistan effective in achieving its objectives give comments? TAX EXEMPTION According To â€Å"Community Benefit† theorists Tax-exemption contributes to pluralism â€Å"by providing the public goods and services that either are undersupplied by the private market or by the government or else not provided in the same socially desirable manner† NEED OF TAX EXEMPTION Tax Exemption is provided for various purposes discussed below which are: ? To Promote Economic activity ? To Provide Benefit to society ? To Provide Corporate Welfare ? To Attract Businesses ? To Promote Organizations ? To Encourage Religious Activities ? To Encourage Economic Activities ? To Encourage Retirement-Led Investment ? To Promote Economic activity Tax exemptions are usually meant to either reduce the tax burden on a particular segment of society in the interests of fairness or to promote some type of economic activity through reducing the tax burden on those organizations or individuals who are involved in that activity. ? To Provide Benefit To Society Tax Exemptions are accorded to certain organizations because they provide a benefit to society which the government is unable or unwilling to provide. ? To Provide Corporate Welfare Tax Exemption to specific businesses such as Big Oil is for corporate welfare. To Attract Businesses Exemption from property tax and other local tax is used as a tool for attracting business to areas suffering from economic down turn or depression. ? To Promote Organizations Tax Exemption is provided to individuals and organizations to promote economically. ? To Encourage Religious Activities Tax exemption is provided to encourage certain social and religious activities. ? To Encourage Economic Activ ities Tax exemption is provided to encourage certain economic activities. ? To Encourage Retirement-Led Investment Tax Exemption is provided on amount of gratuity or commutation of person to encourage retirement-led investments. COMMENTS Ignoring all other factors and emphasizing particularly on tax exemption we can comment that, ? Tax exemption has promoted agriculture sector. Tax is not applied on income generated up to Rs. 80,000, income exceeding from R. s 80,000 will b taxed. The total number of such farmer assesses is reported to be only about 20,000 in the entire country with an average of no more than 200 such agriculture income tax payers per district. Thus tax exemption provides relief to people engaged in tax exemption. ? Tax exemption has promoted scholarships in the country as the ratio of scholarships have increased from last decades which is providing opportunities to many students to not only study in Pakistan but also abroad. Tax exemption from scholarships is beneficial for both students and country. ? Tax exemption has promoted immense foreign investment in Pakistan as China has started many projects in Pakistan not only because of cheap labor but also because of tax exemption. Similarly many other foreign projects are practicing in Pakistan. Tax exemption has promoted many investment banks as Modarba, macro finance bank, national investment trust etc which provide many easy loans to people and firms which in turn contribute in promoting society. ? Tax exemption policy has promoted many sectors as businesses, educational sector, foreign investment, NGO’S etc Thus, We can conclude that present tax exemption policy i s providing many incentives to people, starting new businesses and is encouraging people to invest more and more in various sectors which in turn are generating income to the economy. It is because of tax exemption that many projects have started in special industrial zones in Pakistan as Export processing zone, North Western Industrial zone, Eastern Western Industrial zone and many more. Tax exemption policy in many areas as income earned from foreign enterprise, capital gain by foreign institutional investor, income from transport businesses has widened the approach of business. So present income tax exemption policy of Pakistan is effective in achieving its objectives. [pic]

Girl with Balloons

Street art has become a popular way for artists to express their ideas about society through their public displays of art. Banksy is a well known street artists that displays controversial and political artworks. Banksy work â€Å"girl with balloons† is painted on the Israeli West Bank Barrier Wall, which is a security and separation barrier which is still under construction. Which is almost considered a modern day Berlin Wall. The placement of this image is art, not the artwork itself. If Banksy had used this exact image and placed it somewhere else it wouldn’t have the same effect. Banksy intentions where to make a statement about the relationship between the two cultures. The West Bank Barrier wall is a wall that separates the Israelis from the Palestinians who are having cultural wars with each other. With the use of the young girl flying to freedom it makes people think about their freedom, whether someone who would walk past it or someone looking at it on the internet. Banksy hasn’t used any special techniques to construct his artwork, jus t simply spray cans and a stencil. Anyone could do this. Banksy artwork â€Å"girl with balloons† is simple, but is full of symbolism and meaning. The fact that in this foreign country to him he was able to illeagally put up this artwork without permission shows a sign of the lack of security. The choice of balloons is interesting. Making it seem like if only it were so simply just to float over. But to an adult if only it was that easy. A clown will use balloons to create animals and give them to children. Although lifeless and inanimate, they become somthing real to a childs imagination. Banksy has highlighted the religious troubles that are happening at the moment along the West Bank Barrier Wall. With the use of a simply yet effective artwork, banksy has doubt got people thinking. Banksy placement is the key to this image which inevitably makes it â€Å"art†. http://www. slideshare. net/UWAStudySmarter/essay-structure-for-arts-students http://www. banksy. co. uk/outdoors/index3. html http://people. southwestern. edu/~bednarb/su_netWorks/projects/jle/balloon. html http://iris. lib. neu. edu/cgi/viewcontent. cgi? rticle=1053&context=honors_projects http://artradarjournal. com/2010/01/21/what-is-street-art-vandalism-graffiti-or-public-art-part-i/ http://en. wikipedia. org/wiki/Israeli_West_Bank_barrier THE PLACEMENT OF THIS IMAGE IS ART, NOT THE ARTWORK If the same picture was painted somwhere else it wouldn’t have the same meaning. Culture divide Young child escaping to freedom  · How have contemporary art ideas and issues challenged traditional understandings of artworks and their significance? So people may not consider street art to be art. How does the choice or presentation of subject matter or medium, materials and techniques reflect or challenge artistic or social traditions? Spray cans public property  · What is the impact of dynamic media applications and other emerging art forms on the viewer such as video, digital, projection, installation, interactive, street art, sound and performance art?  · How do these art forms differ from traditional ideas of viewing and experiencing object- based art in museums and galleries?  · How might artworks of the past take on new or different meanings, in the context of contemporary ideas and issues?

Battle of New Orleans in the American Civil War

The capture of New Orleans by Union forces occurred during the American Civil War (1861-1865) and saw Flag Officer David G. Farragut run his fleet past Forts Jackson and St. Philip on April 24, 1862 before capturing New Orleans the following day. Early in the Civil War, Union General-in-Chief Winfield Scott devised the Anaconda Plan for defeating the Confederacy. A hero of the Mexican-American War, Scott called for the blockade of the Southern coast as well as the capture of the Mississippi River. This latter move was designed to split the Confederacy in two and prevent supplies from moving east and west. To New Orleans The first step to securing the Mississippi was the capture of New Orleans. The Confederacys largest city and busiest port, New Orleans was defended by two large forts, Jackson and St. Philip, situated on the river below the city (Map). While forts had historically held an advantage over naval vessels, successes in 1861 at Hatteras Inlet and Port Royal led Assistant Secretary of the Navy Gustavus V. Fox to believe that an attack up the Mississippi would be feasible. In his view, the forts could be reduced by naval gunfire and then assaulted by a relatively small landing force. Foxs plan was initially opposed by US Army general-in-chief George B. McClellan who believed that such an operation would require 30,000 to 50,000 men. Viewing a prospective expedition against New Orleans as a diversion, he was unwilling to release large numbers of troops as he was planning what would become the Peninsula Campaign. To obtain the needed landing force, Secretary of the Navy Gideon Welles approached  Major General Benjamin Butler. A political appointee, Butler was able to use his connections to secure 18,000 men and received command of the force on February 23, 1862. Fast Facts: Capture of New Orleans Conflict: American Civil War (1861-1865)Dates: April 24, 1862Armies Commanders:UnionFlag Officer David G. Farragut17 warships19 mortar boatsConfederateMajor General Mansfield LovellForts Jackson St. Philip2 ironclads, 10 gunboats Farragut The task of eliminating the forts and taking the city fell to Flag Officer David G. Farragut. A long-serving officer who had taken part in the War of 1812 and Mexican-American War, he had been raised by Commodore David Porter following the death of his mother. Given command of the West Gulf Blockading Squadron in January 1862, Farragut arrived at his new post the following month and established a base of operations on Ship Island off the coast of Mississippi. In addition to his squadron, he was provided with a fleet of mortar boats led by his foster brother, Commander David D. Porter, who had the ear of Fox. Assessing the Confederate defenses, Farragut initially planned to reduce the forts with mortar fire before advancing his fleet up the river. Rear Admiral David G. Farragut. US Naval History and Heritage Command   Preparations Moving to the Mississippi River in mid-March, Farragut began moving his ships over the bar at its mouth. Here complications were encountered as the water proved three feet shallower than expected.  As a result, the steam frigate USS Colorado (52 guns) had to be left behind. Rendezvousing at Head of Passes, Farraguts ships and Porters mortar boats moved up the river towards the forts. Arriving, Farragut was confronted by Forts Jackson and St. Philip, as well as a chain barricade and four smaller batteries. Sending forward a detachment from the US Coast Survey, Farragut made determinations on where to place the mortar fleet. Confederate Preparations From the outset of the war, plans for the defense of New Orleans were hampered by the fact that the Confederate leadership in Richmond believed that the greatest threats to the city would come from the north. As such, military equipment and manpower were shifted up the Mississippi to defensive points such as Island Number 10.  In southern Louisiana, the defenses were commanded by Major General Mansfield Lovell who had his headquarters in New Orleans. Immediate oversight of the forts fell to Brigadier General Johnson K. Duncan. Supporting the static defenses were the River Defense Fleet consisting of six gunboats, two gunboats from the Louisiana Provisional Navy, as well as two gunboats from the Confederate Navy and the ironclads CSS Louisiana (12) and CSS Manassas (1). The former, while a powerful ship, was not complete and was used as a floating battery during the battle. Though numerous, the Confederates forces on the water lacked a unified command structure. Reducing the Forts Though skeptical about their effectiveness in reducing the forts, Farragut advanced Porters mortar boats on April 18.  Firing non-stop for five days and nights, the mortars pounded the forts, but were unable to completely disable their batteries. As the shells rained down, sailors from USS Kineo (5), USS Itasca (5), and USS Pinola (5) rowed forward and opened a gap in the chain barricade on April 20. On April 23, Farragut, impatient with the bombardments results, began planning to run his fleet past the forts. Ordering his captains to drape their vessels in chain, iron plate, and other protective materials, Farragut divided the fleet into three sections for the coming action (Map). There were led by Farragut and Captains Theodorus Bailey and Henry H. Bell. Running the Gauntlet At 2:00 AM on April 24, the Union fleet began moving upstream, with the first division, led by Bailey, coming under fire an hour and fifteen minutes later. Racing ahead, the first division was soon clear of the forts, however Farraguts second division encountered more difficulty. As his flagship, USS Hartford (22) cleared the forts, it was forced to turn to avoid a Confederate fire raft and ran aground. Seeing the Union ship in trouble, the Confederates redirected the fire raft towards Hartford causing a fire to break out on the vessel. Moving quickly, the crew extinguished the flames and was able to back the ship out of the mud. USS Hartford (1858). US Naval History Heritage Command Above the forts, the Union ships encountered the River Defense Fleet and Manassas. While the gunboats were easily dealt with, Manassas attempted to ram USS Pensacola (17) but missed. Moving downstream, it was accidentally fired upon by the forts before moving to strike USS Brooklyn (21). Ramming the Union ship, Manassas failed to strike a fatal blow as it hit Brooklyns full coal bunkers. By the time the fighting ended, Manassas was downstream of the Union fleet and unable to make enough speed against the current to ram effectively. As a result, its captain ran it aground where it was destroyed by Union gun fire. The City Surrenders Having successfully cleared the forts with minimal losses, Farragut began steaming upstream to New Orleans. Arriving off the city on April 25, he immediately demanded its surrender. Sending a force ashore, Farragut was told by the mayor that only Major General Lovell could surrender the city. This was countered when Lovell informed the mayor that he was retreating and that the city was not his to surrender. After four days of this, Farragut ordered his men to hoist the US flag over the customs house and city hall. During this time, the garrisons of the Forts Jackson and St. Philip, now cut off from the city, surrendered. On May 1, Union troops under Butler arrived to take official custody of the city. Aftermath The battle to capture New Orleans cost Farragut a mere 37 killed and 149 wounded. Though he was initially unable to get all of his fleet past the forts, he succeeded in getting 13 ships upstream which enabled him to capture the Confederacys greatest port and center of trade. For Lovell, the fighting along the river cost him around 782 killed and wounded, as well as approximately 6,000 captured. The loss of the city effectively ended Lovells career. After the fall of New Orleans, Farragut was able to take control of much of the lower Mississippi and succeeded in capturing Baton Rouge and Natchez. Pressing upstream, his ships reached as far as Vicksburg, MS before being halted by Confederate batteries. After attempting a brief siege, Farragut withdrew back down the river to prevent being trapped by falling water levels.