By Charles Choi, United Press International

NEW YORK (UPI) -- New, oxygen-laced crystals could lead to solar electric panels with nearly double the efficiency of current solar cells. "We would expect this to be most relevant to space applications -- satellites," researcher Kin Man Yu, a materials scientist at Lawrence Berkeley National Laboratory in Berkeley, Calif., told United Press International.

Solar panels use layers of semiconductors to turn sunlight into electricity. Current solar cells convert at an efficiency of about 30 percent. Yu said his team's new crystal could produce efficiencies of up to 56 percent. The key is tuning solar cells to receive wider bandwidths of light. In standard photovoltaic cells, a semiconductor material -- usually silicon -- absorbs daylight, which is converted to power by knocking electrons loose. When electrons move, electrical current flows. Depending on the semiconductor employed in the cell, the light must possess a specific energy, known as its "band gap," to knock out the electrons. Light with lower energy will not be absorbed, while light with higher energy will be absorbed, but its extra energy will be wasted.

The researchers invented a new semiconducting crystal composed of an alloy of zinc, manganese and the relatively rare element tellurium, along with oxygen impurities. The oxygen alters the photovoltaic properties of the material by splitting its one band gap into three. The semiconductor then can take advantage of a wider range of solar energy, Yu explained. Also, adjusting the amount of oxygen in the material can vary the band gaps, so scientists can continue to tinker with the technology and optimize it for sunlight harvesting. "They could probably, with further optimization, get efficiencies of up to 65 or 70 percent," physicist Jacek Furdyna of the University of Notre Dame in South Bend, Ind., told UPI. "It's an entirely new ballgame."

In solar cell parlance, the new semiconductor is a type of II-VI alloy. It has a broad range of band gaps because it contains small quantities of oxygen -- in the parts-per-million range -- which it absorbed from the air during fabrication. Scientists have known for 30 years impurities could split the band gap of a semiconductor, Yu said, allowing it to harvest more energy. Actually synthesizing such a semiconductor was difficult, he added. For oxygen to generate the power-conversion benefits seen in the new alloy, it needed to be present at levels at least 10,000 times higher than usual in II-VI alloys. The problem is oxygen usually bubbles out because it will not combine very well chemically with the semiconductor.

Yu and his Berkeley team solved this chemical conundrum with a novel, laser-based technique. First they create thin films of the untainted alloy. Next, they fire beams of oxygen ions at the film, which forces them into the material. Last, they blast it all with intense laser pulses, which liquefy the film. The pulses are only 30 billionths of a second long, so the semiconductor quickly solidifies, trapping the oxygen atoms in the crystal. "The rapid nature of the process is crucial to achieving such an alloy," said Yu, who with his team describes the findings in an upcoming issue of the journal Physical Review Letters.

The researchers have not yet fabricated a working device using their material but Yu said they hope to partner with several labs to try to build cells, including Notre Dame, Purdue University in West Lafayette, Ind., and the National Renewable Energy Laboratory in Golden, Colo. At this point, the new semiconductor is not cheap, at least when compared with silicon. "The most immediate application would not be solar panels on the roof, because of the expense," Yu said. "In space, the best energy source is solar power, and the cost in that case is not that important compared to the efficiency."

Also, the only way to make the material is with the novel, pulsed-laser melting method. The researchers currently are experimenting with other, more industrially proven fabrication methods, such as molecular beam epitaxy or laser ablation. They also hope to experiment on cheaper materials with similar properties to their new semiconductor. Furdyna said he found the work very exciting.

"It's not something you'll see tomorrow, but I think it's something that will be viable in as soon as the scale of five years," he told UPI. If researchers can create a material with four band gaps, "the efficiency could be over 70 percent," Yu said. "But we don't know how to make such a material yet."