drbubb Posted June 2, 2007 Report Share Posted June 2, 2007 Freiburger Scientists break a Solar Cell World Record Multicrystalline Silicon Solar Cell with an Efficiency Value of 20.3 Percent Today, 55 % of all solar cells throughout the world are produced from multicrystalline silicon. In comparison to monocrystalline silicon, which commands a market share of 35 %, the multicrystalline material is less expensive but contains many more defects such as grain boundaries or dislocations. For this reason, the photovoltaic community has had to be content with efficiency values below 20 % for cells made of multicrystalline silicon, whereas this limit was already exceeded more than 20 years ago for monocrystalline material. Scientists at Fraunhofer ISE in Freiburg, Germany, are now the first to succeed in clearing this hurdle. After two years of work, a doctoral candidate in Stefan Glunz's group on high-efficiency silicon cells, Oliver Schultz, has successfully developed a process which allows the problematic defects to be partially "deactivated". "The trick is to choose temperatures during the solar cell production process such that the electrical properties of the multicrystalline silicon are improved and a high-efficiency solar cell structure is built up at the same time", explained Oliver Schultz. In this way, he has harmonised the high temperatures needed for a highly efficient solar cell with the temperatures that are "acceptable" to the material and are feasible in an industrial production process. Another important role in reaching the goal was played by a process for producing the back-surface contacts of the solar cell, which was also developed and patented by Fraunhofer ISE. So-called LFC technology, where LFC stands for Laser-Fired Contacts, is a industrial feasible process offering the ideal combination of potential for high efficiency values and low production costs. The expensive and slow photolithographic steps, that have been used up to now to produce the back-surface contacts of high-efficiency cells, are no longer needed. The LFC process can already be transferred to industrial production today. Further development steps are still needed to achieve this for the highly efficient front structure. "This barrier was not only physical but also psychological, so we are particularly proud to be the first to have broken through it", stated Gerhard Willeke, Head of the Solar Cell Department. @: http://220.127.116.11/search?q=cache:YTqY9g...t=clnk&cd=4 - - 20.1% efficiency achieved on large area thin silicon wafer PV cell The laser-grooved buried contact (LGBC) crystalline silicon solar cell has a selective emitter with excellent response to the solar spectrum in the wavelength range 300-900 nm. However, the cell efficiency is limited by a reduced response in the 900-1200 nm region of the spectrum due to the high recombination characteristics of the rear aluminium back surface contact and reduced internal reflection at this interface. The LGBC cell has now been fabricated with an aluminium laser-fired contact (LFC) through a passivating rear silicon oxide dielectric. By Nigel Mason, Oliver Schultz, Richard Russell, Stefan Glunz and Wilhelm Warta, BP Solar. @: http://www.insidegreentech.com/node/372 Technical paper : http://www.bp.com/liveassets/bp_internet/s.../2BP_1_1_2_.pdf Abstract : http://de.scientificcommons.org/2142957 Link to comment Share on other sites More sharing options...
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