Researchers at the US Department of Energy's National Renewable Energy Laboratories (NREL, Golden, Colorado, US) have developed a low-cost etching technique that has the potential to increase solar photovoltaic (PV) cell efficiencies while eliminating the use of potent greenhouse gases and reducing costs in the manufacturing process. A research team led by NREL Researcher Howard Branz has developed a new method for creating "black silicon" wafers using an inexpensive wet-etch process, which NREL says can reduce cell reflection to under 2%. "We've had several companies come visit here to learn more about it", said NREL Commercialization and Technology Transfer Division Associate Director of Licensing Chris Harris. "The interest is high. This is certainly a significant advantage in an industry where everyone is competing for market share and the cost per watt is a key selling feature. Black silicon provides an added benefit on top of any other improvements in efficiency a company can get." 

Black silicon process a development of work by the Technical University of Munich

Black silicon is created by etching a large number of tiny holes to absorb light, giving the silicon a black appearance. The NREL process etches roughly a trillion holes for a silicon wafer the size of a compact disc, using a three-minute chloroauric acid bath to etch holes at an average depth of 500 nanometers.

NREL researcher Howard Branz says that the idea for the process came from a scientist at the Technical University of Munich, whose process used a mixture of hydrogen peroxide and hydrofluoric acid with a very thin layer of gold deposited by vacuum deposition. NREL originally used a colloidal mixture of gold and acids, however later moved to the chloroauric acid wet-etch.

Black silicon shows advantages over silane gas process

NREL says that the new approach has the potential to replace a silane gas process, which is more expensive and capital-intensive, and also uses cleaning gases including nitrogen triflouride, an extremely potent greenhouse gas. The organization notes that its silicon wet-etch process is also more effective than the silicon nitride anti-reflection layers which are currently used, which typically allow a minimum of 3-7% reflection. Black silicon further has the advantage of better absorption of low-angle morning and evening light.

NREL says that even with these advantages, the cells the organization has been able to produce with the process still have lower efficiencies than commercial PV cells, in the range of tenths of a percentage lower. However, a number of PV manufacturers have contacted NREL about the process, which won one of Research and Development Magazine's R&D 100 awards in June 2010.

2010-09-09| Courtesy: NREL | solarserver.com © Heindl Server GmbH

Our editorial selection of breaking solar news is published at:
www.solarserver.com/solar-magazine/solar-news/top-solar-news.html