College papers help


Silicon as the most common elements on earth and mostly used in solar cells today

See Article History Solar cell, also called photovoltaic cell, any device that directly converts the energy of light into electrical energy through the photovoltaic effect. The overwhelming majority of solar cells are fabricated from silicon —with increasing efficiency and lowering cost as the materials range from amorphous noncrystalline to polycrystalline to crystalline single crystal silicon forms. Unlike batteries or fuel cellssolar cells do not utilize chemical reactions or require fuel to produce electric powerand, unlike electric generatorsthey do not have any moving parts.

  • Solar panels are slightly less efficient at energy conversion per surface area than individual cells, because of inevitable inactive areas in the assembly and cell-to-cell variations in performance;
  • Using nanotechnology, atoms and molecules can be combined into new materials with very special properties;
  • Although the doping mechanism is not clearly understood, homo- and heterojunction devices have been fabricated based on Si QD [ 24 ];
  • There are several drawbacks to the Siemens process, which include high energy consumption, batch process runs, which means if the process is stopped for any reason, the run is worthless, and a large amount of by-products must be handled.

Solar cells can be arranged into large groupings called arrays. These arrays, composed of many thousands of individual cells, can function as central electric power stations, converting sunlight into electrical energy for distribution to industrial, commercial, and residential users.

  • Silicon is a group IV A element, and the second most abundant element on earth;
  • In order to use this silicon besides controlling the maximum concentrations of different metallic impurities, the research is focusing also on the maximum acceptable concentrations of the doping elements and its effect on material and cell parameters [ 12 , 13 ] Recently, the Hall majority carrier mobility of p-type, compensated multicrystalline solar grade silicon wafers for solar cells in the temperature range 70—373 K has been investigated;
  • Because the back layer also must be a very good electrical conductor, it is always made of metal.

Solar cells in much smaller configurations, commonly referred to as solar cell panels or simply solar panels, have been installed by homeowners on their rooftops to replace or augment their conventional electric supply.

Solar cell panels also are used to provide electric power in many remote terrestrial locations where conventional electric power sources are either unavailable or prohibitively expensive to install. Because they have no moving parts that could need maintenance or fuels that would require replenishment, solar cells provide power for most space installations, from communications and weather satellites to space stations.

  • But due to the higher concentrations of deleterious impurities in MG-Si, new approaches are necessary and have been developed to make cost-effective solar cells from low-cost, but impurity-rich, feedstock;
  • But sand is not the source of silicon metal, the precursor of the ultra high purity 'electronic' grade silicon, which is required for the creation of silicon photovoltaic solar cells, which generate electricity when ordinary sunlight falls on them, and which when wired together in sufficient numbers can be used to power devices far from the nearest coal, oil, or nuclear powered electricity supply grid;
  • Prototype devices have been already realized [ 24 ], but the efficiency obtained is still very low less than 0;
  • By now you must be wondering what all the fuss about a shortage of silicon to make photovoltaic cells for solar power generation can possibly be about;
  • That is when the adverse chemical changes occur;
  • In order to use this silicon besides controlling the maximum concentrations of different metallic impurities, the research is focusing also on the maximum acceptable concentrations of the doping elements and its effect on material and cell parameters [ 12 , 13 ] Recently, the Hall majority carrier mobility of p-type, compensated multicrystalline solar grade silicon wafers for solar cells in the temperature range 70—373 K has been investigated.

Solar power is insufficient for space probes sent to the outer planets of the solar system or into interstellar spacehowever, because of the diffusion of radiant energy with distance from the Sun.

Solar cells have also been used in consumer products, such as electronic toys, handheld calculatorsand portable radios. Solar cells used in devices of this kind may utilize artificial light e.

By December 2000 the major elements of the partially completed station included the American-built connecting node Unity and two Russian-built units—Zarya, a power module, and Zvezda, the initial living quarters. A Russian spacecraft, which carried up the station's first three-person crew, is docked at the end of Zvezda.

The photograph was taken from the space shuttle Endeavour.

Market Data

National Aeronautics and Space Administration While total photovoltaic energy production is minuscule, it is likely to increase as fossil fuel resources shrink. The antireflection layer is typically an oxide of silicontantalumor titanium that is formed on the cell surface by spin-coating or a vacuum deposition technique. Voltage is generated by solar cells made from specially treated semiconductor materials, such as silicon. Courtesy of the National Renewable Energy Laboratory The three energy-conversion layers below the antireflection layer are the top junction layer, the absorber layer, which constitutes the core of the device, and the back junction layer.

Two additional electrical contact layers are needed to carry the electric current out to an external load and back into the cell, thus completing an electric circuit. Since metal blocks light, the grid lines are as thin and widely spaced as is possible without impairing collection of the current produced by the cell.

The back electrical contact layer has no such diametrically opposed restrictions. It need simply function as an electrical contact and thus covers the entire back surface of the cell structure.

Because the back layer also must be a very good electrical conductor, it is always made of metal.

  1. The thickness of the individual layers will vary between a hundred and a thousand nanometres. With this combination, we can utilize 35 to 40 per cent of the sunlight," emphasizes Bengt Svensson.
  2. In principle, it is possible to meet the whole world's energy needs with sunlight. All this is strictly related to the fact that multicrystalline silicon is able to increase the ratio between efficiency and cost most effectively than monocrystalline one.
  3. The first layer will still be composed of silicon cells. The simplest deployment of solar panels is on a tilted support frame or rack known as a fixed mount.
  4. Organic PV is a fast growing research topic with the first companies producing products for consumers.

Since most of the energy in sunlight and artificial light is in the visible range of electromagnetic radiationa solar cell absorber should be efficient in absorbing radiation at those wavelengths. Materials that strongly absorb visible radiation belong to a class of substances known as semiconductors. Semiconductors in thicknesses of about one-hundredth of a centimetre or less can absorb all incident visible light; since the junction-forming and contact layers are much thinner, the thickness of a solar cell is essentially that of the absorber.

Examples of semiconductor materials employed in solar cells include silicon, gallium arsenide, indium phosphide, and copper indium selenide. The addition of junction-forming layers, however, induces a built-in electric field that produces the photovoltaic effect. In effect, the electric field gives a collective motion to the electrons that flow past the electrical contact layers into an external circuit where they can do useful work.

The materials used for the two junction-forming layers must be dissimilar to the absorber in order to produce the built-in electric field and to carry the electric current.

Materials for Solar Photovoltaic Cells I: Silicon, Very Abundant, Very Expensive

Hence, these may be different semiconductors or the same semiconductor with different types of conductionor they may be a metal and a semiconductor. The materials used to construct silicon as the most common elements on earth and mostly used in solar cells today various layers of solar cells are essentially the same as those used to produce the diodes and transistors of solid-state electronics and microelectronics see also electronics: Solar cells and microelectronic devices share the same basic technology.

In solar cell fabrication, however, one seeks to construct a large-area device because the power produced is proportional to the illuminated area. In microelectronics the goal is, of course, to construct electronic components of ever smaller dimensions in order to increase their density and operating speed within semiconductor chips, or integrated circuits. The photovoltaic process bears certain similarities to photosynthesisthe process by which the energy in light is converted into chemical energy in plants.

Since solar cells obviously cannot produce electric power in the dark, part of the energy they develop under light is stored, in many applications, for use when light is not available. One common means of storing this electrical energy is by charging electrochemical storage batteries.

This sequence of converting the energy in light into the energy of excited electrons and then into stored chemical energy is strikingly similar to the process of photosynthesis. Solar panel design Most solar cells are a few square centimetres in area and protected from the environment by a thin coating of glass or transparent plastic.

A solar, or photovoltaic PVmodule generally consists of 36 interconnected cells laminated to glass within an aluminum frame. In turn, one or more of these modules may be wired and framed together to form a solar panel. Solar panels are slightly less efficient at energy conversion per surface area than individual cells, because of inevitable inactive areas in the assembly and cell-to-cell variations in performance.

The back of each solar panel is equipped with standardized sockets so that its output can be combined with other solar panels to form a solar array. A complete photovoltaic system may consist of many solar panels, a power system for accommodating different electrical loads, an external circuit, and storage batteries. Photovoltaic systems are broadly classifiable as either stand-alone or grid-connected systems.

A battery system is essential to compensate for the absence of any electrical output from the cells at night or in overcast conditions; this adds considerably to the overall cost. Each battery stores direct current DC electricity at a fixed voltage determined by the panel specifications, although load requirements may differ.

International Journal of Photoenergy

Stand-alone systems are ideally suited for remote installations where linking to a central power station is prohibitively expensive. Examples include pumping water for feedstock and providing electric power to lighthouses, telecommunications repeater stations, and mountain lodges. Grid-connected systems integrate solar arrays with public utility power grids in two ways.

One-way systems are used by utilities to supplement power grids during midday peak usage. Bidirectional systems are used by companies and individuals to supply some or all of their power needs, with any excess power fed back into a utility power grid. A major advantage of grid-connected systems is that no storage batteries are needed. The corresponding reduction in capital and maintenance costs is offset, however, by the increased complexity of the system.

Inverters and additional protective gear are needed to interface low-voltage DC output from the solar array with a high-voltage AC power grid. Additionally, rate structures for reverse metering are necessary when residential and industrial solar systems feed energy back into a utility grid.

A grid-connected solar cell system. The simplest deployment of solar panels is on a tilted support frame or rack known as a fixed mount.

The world's most efficient and environment-friendly solar cells

For maximum efficiency, a fixed mount should face south in the Northern Hemisphere or north in the Southern Hemisphere, and it should have a tilt angle from horizontal of about 15 degrees less than the local latitude in summer and 25 degrees more than the local latitude in winter. More complicated deployments involve motor-driven tracking systems that continually reorient the panels to follow the daily and seasonal movements of the Sun.

Such systems are justified only for large-scale utility generation using high-efficiency concentrator solar cells with lenses or parabolic mirrors that can intensify solar radiation a hundredfold or more. Although sunlight is free, the cost of materials and available space must be considered in designing a solar system; less-efficient solar panels imply more panels, occupying more space, in order to produce the same amount of electricity. Compromises between cost of materials and efficiency are particularly evident for space-based solar systems.

In addition, minimizing the liftoff weight of these panels is more critical than fabrication costs. Amorphous silicon is very attractive from this viewpoint. In particular, amorphous silicon-coated roof tiles and other photovoltaic materials have been introduced in architectural design and for recreational vehicles, boats, and automobiles. Becquerel discovered the photovoltaic effect while experimenting with a solid electrode in an electrolyte solution; he observed that voltage developed when light fell upon the electrode.

About 50 years later, Charles Fritts constructed the first true solar cells using junctions formed by coating the semiconductor selenium with an ultrathin, nearly transparent layer of gold. Appleyard wrote of the blessed vision of the Sun, no longer pouring his energies unrequited into space, but by means of photo-electric cells…, these powers gathered into electrical storehouses to the total extinction of steam engines, and the utter repression of smoke.

By 1927 another metal-semiconductor-junction solar cell, in this case made of copper and the semiconductor copper oxide, had been demonstrated. By the 1930s both the selenium cell and the copper oxide cell were being employed in light-sensitive devices, such as photometersfor use in photography.

These early solar cells, however, still had energy-conversion efficiencies of less than 1 percent. This impasse was finally overcome with the development of the silicon solar cell by Russell Ohl in 1941.

Thirteen years later, aided by the rapid commercialization of silicon technology needed to fabricate the transistorthree other American researchers—Gerald Pearson, Daryl Chapin, and Calvin Fuller—demonstrated a silicon solar cell capable of a 6 percent energy-conversion efficiency when used in direct sunlight.

By silicon as the most common elements on earth and mostly used in solar cells today late 1980s silicon cells, as well as cells made of gallium arsenide, with efficiencies of more than 20 percent had been fabricated.

In 1989 a concentrator solar cell in which sunlight was concentrated onto the cell surface by means of lenses achieved an efficiency of 37 percent owing to the increased intensity of the collected energy.

By connecting cells of different semiconductors optically and electrically in series, even higher efficiencies are possible, but at increased cost and added complexity. In general, solar cells of widely varying efficiencies and cost are now available.