http://www.cbc.ca/technology/story/2006/12/06/solar-cell.html

New solar cells break efficiency records
Last Updated: Wednesday, December 6, 2021 | 10:54 AM ET
Breakthroughs in solar cell efficiency could make solar power a competitive part of the energy market, with two separate groups announcing record results this week.
The U.S. Department of Energy announced Tuesday that a concentrator solar cell produced by Boeing-Spectrolab has achieved a world-record conversion efficiency of 40.7 per cent. The next day, Australian scientists said a commerically available thin solar sheet was capable of over 20 per cent efficiency.

Conversion efficiency measures the percentage of energy from sunlight that is converted into electricity.

Most commercially available solar cells rely solely on natural light and typically reach a top efficiency of 12 per cent to 18 per cent. But concentrator cells, which focus light from the sun, have reached efficiencies approaching 40 per cent.

"Reaching this milestone heralds a great achievement for the Department of Energy and for solar energy engineering worldwide," said Alexander Karsner, the assistant secretary for energy efficiency and renewable energy at the U.S. department of energy.

"We are eager to see this accomplishment translate into the marketplace as soon as possible - [it] has the potential to help reduce our nation's reliance on imported oil and increase our energy security."

The new record in efficiency is seen as a first step to creating affordable systems, with an installation cost of $3 US per watt and capable of producing electricity at a cost of eight to 10 cents per kilowatt hour, or roughly the same price as the cost of natural gas.
An alternative to fossil fuels

The current lack of efficiency in commercial cells has made solar energy an impractical solution as a replacement for fossil fuels such as oil, natural gas and coal.

However, interest in the technology has remained because of the seemingly limitless supply of energy available from the sun and its minimal pollution footprint.

The most basic photovoltaic solar panels use semiconductors such as silicon to absorb light particles - or photons - from the sun. The energy from these photons knocks loose electrons in the silicon, which are induced to follow one direction to create an electric current. Metal contacts attached to the semiconductor draw the current off for external use.

Prof. Andrew Blakers, director of the Centre for Sustainable Energy Systems at the Australian National University, announced on Wednesday a new cell using "sliver technology" could reduce the cost of producing solar cells by more than 60 per cent.

The sliver panels take a standard solar cell and cut tiny slices just 120 micrometres wide into it to provide the cell with more surface area, and therefore more opportunity to absorb the sun's rays. The researchers said they have achieved efficiencies of over 20 per cent, making it the most efficient among commercially available thin-film solar cells.

The Boeing-Spectrolab cell is more complex. Called a multi-junction cell, it is made up of super-thin individual layers, each of which captures part of the sunlight passing through the cell. This allows the cells to capture more of the solar spectrum, the researchers said.

In 1995, Boeing-Spectrolab had reached 39.0 efficiency with a multi-junction concentrator cell capable of focusing sunlight as if light from 236 suns was hitting the cell.

Earlier this year, U.S. President George W. Bush announced plans for a Solar America Initiative with a mandate to gain nationwide acceptance of solar energy technologies by 2015.