U.S. Department of Energy - Energy Efficiency and Renewable EnergySolar Energy Technologies ProgramCrystalline Silicon
The solar cell is the basic building block of a photovoltaic system. Individual cells can vary in size from about 1 cm (1/2 inch) to about 10 cm (4 inches) across. This crystalline silicon cell was manufactured by Siemens Solar Industries. 
Photovoltaics: contributing to the sustainability of global civilization by providing clean, abundant energy every place the sun shines. Crystalline silicon modules produced in the U.S. dominate the world market for PV. The Sacramento Municipal Utility District (SMUD) installed this 210-kilowatt crystalline silicon PV system at its Hedge substation in California. Many areas within the crystalline silicon (c-Si) field are ripe for R&D improvements:
The technology is advancing through research on materials, devices, and processes. By improving the starting material, we improve devices made with the material. By improving devices, we increase efficiencies and decrease fabrication costs. And by improving processes, we also reduce costs. For example, expensive laboratory cells have achieved efficiencies as high as 24.7%, whereas commercially produced cells typically have efficiencies less than 16%. The trick is to develop fabrication processes and device structures that can translate some of the performance features of laboratory cells into manufacturing. Researchers continue to explore highly versatile techniques—such as plasma processing, which can etch surfaces, deposit dielectric coatings, and passivate surface and bulk defects—to form high-efficiency cell structures using manufacturing procedures. This can be thought of as developing new processes that require less energy, material, and labor than conventional approaches and that will result in greater throughput. The goal is to double the output of a manufacturing plant without increasing its size; this will help industry reduce manufacturing costs while increasing output. One research approach that could help reach this goal is rapid thermal processing—a low-cost method that uses high-intensity light to rapidly heat substrates and optically enhance processing steps. Researchers are also investigating radically new device structures that have the potential to significantly reduce the cost of cells and modules. Although the Solar Program and its partners have continually reduced costs, it has been done largely through constant refinement in production processes. New approaches based on cells and modules specifically designed for easy manufacturability will considerably simplify the assembly of PV modules and can continue to reduce costs. Another approach is thin-film silicon, combining the low cost of thin films with the high efficiency of crystalline silicon. Innovative designs use low-cost substrates and special techniques that trap light in silicon for total absorption. With proper light-trapping, silicon as thin as 2 micrometers—which is 100-200 times thinner than traditional crystalline silicon—can be used while aiming for reasonable efficiencies. Although this approach is relatively new, cell efficiencies are approaching about 10%. Further work will emphasize both efficiency (15%-efficient cells are needed to make 10%-efficient modules) and increased film-deposition rates to make economical modules. This area may also merge into the amorphous silicon (a-Si) area by providing new hybrid approaches that benefit from both c-Si and a-Si, and lend themselves to multijunction approaches. To learn more about PV materials, see: |