Spray on Solar Power Cells Term Paper

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Spray-On Solar Power Cells

A solar cell, or photovoltaic cell, is a semiconductor device consisting of a large-area p-n junction diode, which, in the presence of sunlight is capable of generating usable electrical energy. This conversion is called the photovoltaic effect. The field of research related to solar cells is known as photovoltaics.

Solar cells have many applications. They are particularly well suited to, and historically used in situations where electrical power from the grid is unavailable, such as in remote area power systems, Earth orbiting satellites, handheld calculators, remote radiotelephones, water pumping applications, etc. Solar cells, in the form of modules or solar panels, are appearing on building roofs where they are connected through an inverter to the electricity grid in a net metering arrangement.

Various materials have been investigated for solar cells. There are two main criteria - efficiency and cost. Efficiency is a ratio of the electric power output to the light power input. Ideally, near the equator at noon on a clear day, the solar radiation is approximately 1000 W/m2. So a ten percent efficient module of one square meter can power a 100-watt light bulb. Costs and efficiencies of the materials vary greatly. By far the most common material for solar cells (and all other semiconductor devices) is crystalline silicon. Crystalline silicon solar cells come in three primary categories. Single crystal or monocrystalline wafers are made using the Czochralski process. Most commercial monocrystalline cells have efficiencies on the order of 14%. The SunPower cells have high efficiencies around 20%. Single crystal cells tend to be expensive, and because they are cut from cylindrical ingots, they cannot completely cover a module without a substantial waste of refined silicon.

Most monocrystalline panels have uncovered gaps at the corners of four cells. Poly or multi-crystalline made from cast ingots - large crucibles of molten silicon carefully cooled and solidified. These cells are cheaper than single crystal cells, but also somewhat less efficient, however, they can easily be formed into square shapes that cover a greater fraction of a panel than monocrystalline cells, and this compensates for their lower efficiencies. Ribbon silicon is formed by drawing flat thin films from molten silicon and has a multicrystalline structure. These cells are typically the least efficient, but there is a cost savings since there is very little silicon waste because this approach does not require sawing from ingots. These technologies are wafer-based manufacturing. In other words, in each of the above approaches, self-supporting wafers of ~300 micrometers thick are fabricated and then soldered together to form a module.

Thin film approaches are module based. The entire module substrate is coated with the desired layers and a laser scribe is then used to delineate individual cells. Two main thin film approaches are amorphous silicon films and general chalcogenide films of Cu (InxGa1-x)(SexS1-x) 2, or CIS. Amorphous silicon films are fabricated using chemical vapor deposition techniques, typically plasma enhanced (PE-CVD). These cells have low efficiencies of around eight percent. While the CIS films can achieve 11% efficiency, their costs are still too high. There are additional materials and approaches on the horizon, for example, Sanyo has pioneered the HIT cell. In this technology, amorphous silicon films are deposited onto crystalline silicon wafers.

"Nano" refers to one billionth of a meter: the size of a few atoms clustered together to form a molecule. Nanotechnology is potentially more revolutionary than just miniaturization. Atoms and molecules are dominated by different forces, and governed by different rules, when they interact on the scale of the nanometer. In living organisms, atoms and molecules organize themselves into proteins, tissues, and ultimately living, thinking, emoting beings.

Nanotechnology comprises technological developments on the nanometer scale, usually 0.1 to 100 nm. One nanometer equals one thousandth of a micrometer or one millionth of a millimeter. The term nanotechnology is often used interchangeably with molecular nanotechnology, also known as "MNT," a hypothetical, advanced form of nanotechnology believed to be achievable at some point in the future. Molecular nanotechnology includes the concept of mechanosynthesis. The term nanoscience is used to describe the interdisciplinary field of science devoted to the advancement of nanotechnology.

Nanotechnologists are seeking to harness the same principles to prompt matter into constructing itself. Atoms and molecules don't obey the laws of physics we experience day-to-day: instead they reveal in their behavior the mysterious, surprising rules of quantum mechanics. Nanotechnologists turn quantum mechanics' rules to advantage to build new materials, chips, and medical treatments tailored to society's needs.

The size scale of nanotechnology makes it susceptible to quantum-based phenomena, often leading to counterintuitive results. These nanoscale phenomena may include quantum size effects and molecular forces such as Van der Waals forces. Furthermore, the vastly increased ratio of surface area to volume opens new possibilities in surface-based science, such as catalysis. "An increase in funding for basic research in this important new field, as well as a handful of Nobel Prizes awarded to scientists who are pursuing it, has caused many to believe nanotechnology is coming into its own."

Researchers at the University of Toronto have invented an infrared-sensitive material that is five times more efficient at turning the sun's power into electrical energy than current methods. The discovery could lead to shirts and sweaters capable of recharging our cell phones and other wireless devices, said Ted Sargent, professor of electrical and computer engineering at the University of Toronto. Existing technology has given us solution-processible, light-sensitive materials that have made large, low-cost solar cells, displays, and sensors possible, but these materials have so far only worked in the visible light spectrum, says Sargent. "These same functions are needed in the infrared for many imaging applications in the medical field and for fiber optic communications,"

he said. The discovery may also help in the quest for renewable energy sources. Flexible, roller-processed solar cells have the potential to harness the sun's power, but efficiency, flexibility and cost are going to determine how that potential becomes practice, says Josh Wolfe, Managing Partner and nanotechnology venture capital investor at Lux Capital in Manhattan. Wolfe, who was not part of the research team, says the findings in the A nanometer-resolved microscope image of a nanoparticle, or quantum dots, similar to that used to make the infrared detectors. The particle is six nanometers -- billionths of a meter -- in diameter. Individual columns of bonded lead and sulfur atoms are resolved in the image. Such nanoparticles were suspended in a solvent and dried like paint to make a large-area device. Image courtesy of M.A. Hines & G.D. Scholes, Advanced Materials (2003) 15, 1845.

paper are significant: "When you have a material advance which literally materially changes the way that energy is absorbed and transmitted to our devices... somebody out there tinkering away in a bedroom or in a government lab is going to come up with a great idea for a new device that will shock us all."

The plastic material uses nanotechnology and contains the first solar cells able to harness the sun's invisible, infrared rays, five times more efficient than current solar cell technology. Like paint, the composite can be sprayed onto other materials and used as portable electricity. The researchers envision that one day "solar farms" consisting of the plastic material could be rolled across deserts to generate enough clean energy to supply the entire planet's power needs. Professor Peter Peumans of Stanford University, who has reviewed the University of Toronto team's research, also acknowledges the groundbreaking nature of the work. "Our calculations show that, with further improvements in efficiency, combining infrared and visible photovoltaics could allow up to 30 per cent of the sun's radiant energy to be harnessed, compared to six per cent in today's best plastic solar cells."

The sun that reaches the Earth's surface delivers 10,000 times more energy than we consume.…[continue]

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