Solar cells with high conversion efficiency Sanyo Electric Co. Ltd., Japan, has broken its own record to achieve the world’s highest energy conversion efficiency in practical size (100 cm2 or higher) crystalline silicon-type solar cells. Its proprietary HIT solar photovoltaic cells have achieved an efficiency of 22 per cent (until now 21.8 per cent) at a research level. Moreover, this increase in solar cell conversion efficiency is accompanied by significant reductions in the production cost of the photovoltaic (PV) system as well as in the use of raw materials such as silicon. Source: www.jarn.co.jp Plastic tandem organic solar cells A discovery made at the Centre for Polymers and Organic Solids at the University of California, the United States, has given a significant hike in efficiency to organic solar cells. Prof. Alan Heeger worked with Dr. Lee Kwang-hee of the Gwangju Institute of Science and Technology, Republic of Korea, and other scientists to create the “tandem” organic solar cell with increased efficiency. Tandem cells comprise two multi-layered parts that work together to gather a wider range of the solar radiation spectrum – at both shorter and longer wavelengths – resulting in 6.5 per cent efficiency. This is the highest level achieved for solar cells made from organic materials. The new tandem architecture improves light harvesting and promises to be less expensive to produce. The cells can be fabricated to extend over a large area using low-cost printing and coating technologies that can simultaneously pattern the active materials on lightweight flexible substrates. The multi-layered device is the equivalent of two cells in series, states Prof. Heeger. The deposition of each layer of the multiple layers by processing the materials from solution promises to make the solar cells less expensive to produce. Source: www.azom.com Economical process to make non-silicon-based solar cells In Japan, a team led by Mr. Shigeru Niki and Mr. Shogo Ishizuka at the Centre for Photovoltaics, Institute of Advanced Industrial Science and Technology (AIST) has developed a thin-film technology that can lower the consumption of selenium raw materials below 1/10th of the conventional standard during the manufacture of non-silicon-based CIGS thin-film solar cells. This makes it possible to expect mass production of high-performance CIGS modules. CIGS solar cells use Cu(In, Ga)Se2 as the light absorption layer. The new technology was developed for the better control and efficient use of selenium raw materials in the multi-source evaporation method at the AIST. The team replaced conventional vaporized selenium with selenium radicals made using RF plasma cracking to produce CIGS thin films. With this technology, on/off control of selenium supply during production of the thin film is possible. As the high reactivity of radical selenium can be utilized, the scientists succeeded in controlling the consumption of raw materials to a tenth of the amount of conventional vaporized selenium. This also meant that safety in handling selenium can be improved. Metal raw materials, except selenium, still use the same conventional vapour of Knudsen-cell source. It has been found that the CIGS thin film produced using the new technology (using selenium radical) shows a smooth and dense surface and has large grains. The small-area solar cells made with the CIGS thin-film technology shows conversion efficiency as high as the conventional CIGS solar cells. Source: www.aist.go.jp Bio-based prototype solar cell Biosolar Inc., the United States, has created the world’s first bio-based solar cell. The thin-film, flexible solar cell is manufactured on bio-based plastic substrate by laminating the company’s proprietary bio-based substrate on to a crystalline solar cell as back sheet. The processes used to laminate solar cells to back sheets and front cover usually occur at a higher temperature than most bio-based films can withstand. However, Biosolar bio-based films can withstand the harsh environment of the photovoltaic lamination oven. Working solar cells can be made using Biosolar’s bio-based film as part of the packaging for crystalline silicon-based PV modules. The three fully functional prototype solar cell modules that use Biosolar’s proprietary bio-based back sheets have performed to the cell specifications. Contact: Biosolar Inc., 27936, Lost Canyon Road, Suite #202, Santa Clarita, CA 91387, United States of America. Tel: +1 (661) 2510 001; Fax: +1 (661) 2510 003. Source: www.renewableenergyaccess.com Solar cells with metal wrap through technology Researchers at the Fraunhofer Institute for Solar Energy Systems (ISE), Germany, have successfully developed a multi-crystalline solar cell prototype with rear side contacts. In comparison to the production of standard solar cells, there are three process stages for manufacturing the metal wrap through (MWT) solar cells that partially shift the front side contacts over to the rear side, thus reducing the front side metallization almost in half. First, a laser is used to drill holes into the cells. The through connection of the cells is achieved by the subsequent silk screen printing process for the production of the rear side contacts. The silk screen printing paste is used to fill the recently created holes, thus establishing the electrical connection to the front side. Unlike the typical processes, isolation of the contacts reduces additional costs. The rear side contact of the MWT solar cells needs a small modification of the standard process. The first prototype MWT cells achieved an efficiency of more than 16 per cent. This is an increase of up to 0.5 per cent over comparable standard silk screen printed solar cells made of the same multicrystalline material. Source: www.renewableenergyaccess.com Thin-layer solar cells for cheaper green power The experts at Durham University, the United Kingdom, are developing light-absorbing materials for use in the production of thin-layer solar photovoltaic (PV) cells, which are used to convert light energy into electricity. The project involves experiments on a range of different materials that would be less expensive and more sustainable to use in the manufacture of solar panels. It focuses on developing thin-layer PV cells using materials such as copper indium diselenide and cadmium telluride. Professor Ken Durose, Director of the Durham Centre for Renewable Energy, who is leading the research, stated: “One of the main issues in solar energy is the cost of materials and we recognize that the cost of solar cells is slowing down their uptake.” The Durham team is thus working on manipulating the growth of the materials so that they form a continuous structure, which is vital for conducting the energy trapped by solar panels before it is turned into usable electricity. This will help improve the efficiency of the thin-layer PV cells, and lead to the development of more affordable thin-film PV cells for making solar panels that could be fitted to roofs to help power homes. Source: www.sciencedaily.com New technology cuts the price of solar energy A test installation that operates with a linear, 100 m long Fresnel reflector has been installed at Almería in southern Spain. Researchers from the Fraunhofer Institute for Solar Energy Systems (ISE), Germany, helped develop the technology. In sunny countries, it is worthwhile building large-scale solar thermal power plants in whose solar fields thermo-oil is heated. Steam created using a heat exchanger then drives a turbine to generate electricity. Up to now, gigantic parabolic mirrors were used to focus the sunlight on a central absorber tube. Fresnel reflectors offer a low-cost alternative. Flat mirrors arrayed in long rows are so aligned that, with the aid of a small secondary mirror, they focus the sunlight on a tube running along the row of mirrors. Water is vaporized directly in this tube and heated up to 450ºC at high pressure. Prof. Eicke Weber, Director of ISE, says that linear Fresnel reflectors are cheaper than parabolic mirrors, take up less space and less sensitive to the wind. The demonstration plant in Almería was designed by Prof. Weber and his team in collaboration with other prestigious research groups. If the Fresnel reflectors pass muster, they can be used in the construction of commercial solar thermal power plants. Contact: Mr. Karin Schneider, Fraunhofer-Institut fur Solare Energiesysteme (ISE), Heidenhofstraße 2, 79110 Freiburg, Germany. Tel: +49 (761) 4588 5147 Website: www.ise.fraunhofer.den Source: www.fraunhofer.de