01 December 2011
Kaneka Corporation and the Interuniversity Microelectronics Centre (imec) presented silver-free heterojunction silicon solar cells at the 21st International Photovoltaic Science and Engineering Conference held in Fukuoka, Japan. Measurements performed at imec showed a conversion efficiency of more than 21% from the solar cells in 6-inch silicon substrates with an electroplated copper contact grid on top of the transparent conductive oxide layer.
Kaneka’s Photovoltaics European Laboratory is located at the imec campus in Leuven, Belgium. The copper electroplating technology used for the solar cells was developed by Kaneka and based on existing technology from imec.
“The bulk of today’s standard silicon solar cell efficiencies are in the range of 16% to 18%,” said Philip Pieters, Business Development Director at imec. “A couple of companies have products with cell efficiencies above 20% commercially available, but these cells are significantly more expensive. The aim of imec’s developments is to achieve similar or higher efficiencies with lower cost technology solutions.”
Silver screen printing is typically used to create the top grid electrode in heterojunction silicon solar cells. However, it is difficult to lower the resistivity and to thin the metal line using silver screen printing, which had posed a challenge to achieving high efficiency and low cost from this type of solar cell. “Because of the growth of the photovoltaic market the price silver has increased tremendously, and market extrapolations predict a scarcity of silver in the future that will even further increase the silver price,” said Pieters. “Copper is the most logical candidate to take over because of its abundant availability, its lower resistivity and the processing experience we have built-up from semiconductors.”
Using copper-electroplating instead of screen-printed silver to form the top grid electrode overcomes the disadvantages of the silver screen printing and could enable higher efficiencies and lower fabrication costs. To bring the new technology to commercial products requires solving some of the challenges associated with copper, said Pieters. This includes proving that it can meet the long-term reliability requirements for solar cells and developing cost-effective production technologies.
“We believe this will be feasible because of the existing material knowledge experience and the existing electroplating experience in the R&D institutes like imec and in the industry,” said Pieters. “By leveraging on this experience, the use of copper in commercial solar cell products may become sooner than some think.”
Written by Nancy Lamontagne, Contributing Editor - US