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Posted: June 2, 2008
N-type junction solar cell efficiency raises to 23.2%
(Nanowerk News) Physicist Bram Hoex and colleagues at Eindhoven University of Technology (TU/e), together with the Fraunhofer Institute for Solar Energy Systems in Freiburg, Germany, have improved the efficiency of an important type of solar cell (n-type with front junction) from 21.9 to 23.2 per cent (a relative improvement of 6 per cent). This new record was presented on Wednesday 14 May at a major solar energy conference in San Diego, USA. The efficiency improvement is achieved by the use of an ultra-thin aluminum oxide layer at the front of the cell, and it brings a breakthrough in the use of solar energy a step closer.
An improvement of more than 1 per cent (in absolute terms) may at first glance appear modest, but it can enable solar cell manufacturers to greatly increase the performance of their products. This is because higher efficiency is a very effective way of reducing the cost price of solar energy. The costs of applying the thin layer of aluminum oxide are expected to be relatively low. This will mean a significant reduction in the cost of producing solar electricity.
Hoex was able to achieve the increase in efficiency by depositing an ultra-thin layer (approximately 30 nanometer) of aluminum oxide on the front of a crystalline silicon solar cell, that was fabricated by PhD-student Jan Benick (28) at Fraunhofer ISE. This layer has an unprecedented high level of built-in negative charges, through which the – normally significant – energy losses at the surface are almost entirely eliminated. Of all sunlight falling on these cells, 23.2 per cent is now converted into electrical energy. This was formerly 21.9 per cent, which means a 6 per cent improvement in relative terms.
Dutch company OTB Solar
Hoex gained his PhD on 8 May at the Applied Physics department of the TU/e for his work in the Plasma & Materials Processing (PMP) group lead by professor Richard van de Sanden and assistant professor Erwin Kessels. This group specializes in the growth of extremely thin layers. An important process developed by the PMP-group for the deposition of the silicon nitride antireflection coating is currently licensed by the Dutch company OTB Solar and is employed by various leading solar cell manufacturers. The ultra-thin aluminum oxide layer developed in the PMP group may lead to a technology innovation in the solar cell world. A number of major solar cell manufacturers have already shown interest.
Solar cells have for years looked like a highly promising way to partly solve the energy problem. The sun rises day after day, and solar cells can conveniently be installed on surfaces with no other useful purpose. Solar energy also offers opportunities for use in developing countries, many of which have high levels of sunshine. Within ten to fifteen years the price of electricity generated by solar cells is expected to be comparable to that of ‘conventional’ electricity from fossil fuels. This technology breakthrough now brings the industrial application of this type of high-efficiency solar cell closer. For this reason, part of Hoex’s PhD research project was paid for by three Dutch ministries: Economic Affairs; Education, Culture and Science; and Housing, Spatial Planning and the Environment.