Surface and bulk passivation of multicrystalline silicon solar cells by ...
Surface and bulk passivation of multicrystalline silicon solar cells by ... Surface and bulk passivation of multicrystalline silicon solar cells by ...
CHAPTER 1 INTRODUCTION 1.1 Solar Cells-A Perspective As the world becomes more concerned about the environmental effects of burning fossil fuels, and as fossil fuels become scarcer, we need to develop alternate energy technologies. One of the most promising is photovoltaic (PV) or solar cells that are already in use in many places. Solar photovoltaic energy conversion is a one-step conversion process which generates electrical energy from light energy. The explanation relies on ideas from quantum theory. Light is made up of packets of energy, called photons, whose energy depends on the frequency of light. The energy of photons in visible wavelengths is sufficient to excite electrons to higher energy levels where they are freer to move. Photovoltaic technology actually dates back over 160 years. The PV effect was first discovered and reported in 1839 by French physicist A.E. Becquerel [1] when he observed that certain materials would produce a small current when exposed to light. About 55 years later, in 1883, the first solar cell was built by Charles Fritts [2], an American inventor, by coating selenium wafers with an ultrathin, nearly transparent layer of gold to form a metal-semiconductor junction. Fritts's devices were very inefficient, transforming less than 1 percent of the absorbed light into electrical energy. In 1918, a Polish scientist, Jan Czochralski [3] discovered a method for monocrystalline silicon production, which enabled the production of monocrystalline silicon solar cells. In 1941, the first silicon solar cell was invented by Russell Ohl [4]. Silicon proved to be a much better semiconductor and is the predominant material that is used today in solar cells. Ohl was able to obtain energy conversions of less than one 1
2 percent; however, soon, more advances were made in order to increase PV energy conversion efficiencies. In 1954, a silicon solar cell capable of 6% energy conversion efficiency with direct sunlight was invented by three American scientists, Gerald Pearson, Calvin Fuller and Daryl Chapin [5]. They created the first solar panel by putting several strips of silicon p-n junctions together to form an array and placed it in sunlight. The first field trial of the Bell Solar Battery in actual service began on a telephone carrier system in October, 1955 [6]. The first sun-powered automobile was demonstrated in Chicago, Illinois in August 1955 [7]. In 1958, Hoffman Electronics achieved 9% efficient PV cells. Vanguard I, the first PV-powered satellite, was launched in cooperation with the U.S. Signal Corp. The satellite power system operated for eight years [7, 8]. The first telephone repeater powered by solar cells was built In Americus, Georgia [7]. In 1959, Hoffman Electronics achieved 10% efficient, commercially available PV cells. Hoffman Electronics also learned to use a grid contact, reducing the series resistance significantly [7]. On August 7 th 1959, the Explorer VI satellite was launched with a PV array of 9600 solar cells. On October 13 th 1959, Explorer VII was launched [7]. In 1960, Hoffman Electronics introduced yet another solar cell with 14% efficiency [7]. In 1963, Sharp Corporation developed the first usable photovoltaic module from silicon solar cells [9]. In 1985, researchers at the University of New South Wales in Australia constructed a solar cell with more than 20% efficiency [10]. By the late 1980s, silicon solar cells, as well as those made of gallium arsenide, with efficiencies of more than 20 % had been fabricated [11, 12]. In 1989, a concentrator solar cell, a type of device in which sunlight is concentrated onto the cell surface by means of lenses, achieved an efficiency of 37% due to the increased intensity of the collected energy [13]. In general, solar cells of widely
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- Page 3 and 4: ABSTRACT SURFACE AND BULK PASSIVATI
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- Page 9 and 10: Chuan Li, B.L. Sopori, P. Rupnowski
- Page 11 and 12: ACKNOWLEDGEMENT The work presented
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- Page 27 and 28: 8 Figure 1.4 The I-V characteristic
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- Page 47 and 48: 28 Figure 2.5 Deposition of SiΝ :
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- Page 61 and 62: 42 σ and σp are the capture cross
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CHAPTER 1<br />
INTRODUCTION<br />
1.1 Solar Cells-A Perspective<br />
As the world becomes more concerned about the environmental effects <strong>of</strong> burning<br />
fossil fuels, <strong>and</strong> as fossil fuels become scarcer, we need to develop alternate energy<br />
technologies. One <strong>of</strong> the most promising is photovoltaic (PV) or <strong>solar</strong> <strong>cells</strong> that are<br />
already in use in many places.<br />
Solar photovoltaic energy conversion is a one-step conversion process which<br />
generates electrical energy from light energy. The explanation relies on ideas from<br />
quantum theory. Light is made up <strong>of</strong> packets <strong>of</strong> energy, called photons, whose energy<br />
depends on the frequency <strong>of</strong> light. The energy <strong>of</strong> photons in visible wavelengths is<br />
sufficient to excite electrons to higher energy levels where they are freer to move.<br />
Photovoltaic technology actually dates back over 160 years. The PV effect<br />
was first discovered <strong>and</strong> reported in 1839 <strong>by</strong> French physicist A.E. Becquerel [1]<br />
when he observed that certain materials would produce a small current when exposed<br />
to light. About 55 years later, in 1883, the first <strong>solar</strong> cell was built <strong>by</strong> Charles Fritts<br />
[2], an American inventor, <strong>by</strong> coating selenium wafers with an ultrathin, nearly<br />
transparent layer <strong>of</strong> gold to form a metal-semiconductor junction. Fritts's devices were<br />
very inefficient, transforming less than 1 percent <strong>of</strong> the absorbed light into electrical<br />
energy. In 1918, a Polish scientist, Jan Czochralski [3] discovered a method for<br />
monocrystalline <strong>silicon</strong> production, which enabled the production <strong>of</strong> monocrystalline<br />
<strong>silicon</strong> <strong>solar</strong> <strong>cells</strong>. In 1941, the first <strong>silicon</strong> <strong>solar</strong> cell was invented <strong>by</strong> Russell Ohl [4].<br />
Silicon proved to be a much better semiconductor <strong>and</strong> is the predominant material that<br />
is used today in <strong>solar</strong> <strong>cells</strong>. Ohl was able to obtain energy conversions <strong>of</strong> less than one<br />
1