Total repair

时间:2019-03-07 04:12:00166网络整理admin

By Robert Adler ATOMS that repair radiation damage as they wander through semiconductors could lead to cheaper, more efficient and longer-lasting solar power cells, say researchers in Israel. Scientists trying to make better solar cells have long been intrigued by a complex semiconductor called CIGS (copper indium gallium diselenide). This absorbs light more efficiently than silicon, works well in very thin films and is surprisingly stable even when exposed to intense radiation—for example, in space. The mystery of the material’s stability has now been solved, says chemist David Cahen at the Weizmann Institute of Science in Tel Aviv. The secret of CIGS is its remarkable ability to repair itself. Cahen and his colleagues describe in the current issue of Advanced Materials (vol 11, p 957) how they used intense X-rays to probe CIGS and a material with very similar properties, copper indium diselenide (CIS). The researchers found that some of the chemical bonds can be broken quite easily, freeing copper atoms to wander through the crystals. They saw radioactive copper-64 speeding through the semiconductor nearly 20 orders of magnitude faster than materials added to silicon. “The remarkable thing,” says Cahen, “is that you can have a high-quality electronic material with these atoms running around.” The material repairs itself, Cahen found, because the natural tendency of the copper atoms to distribute themselves evenly means that they spread into damaged spots in the crystal, where their presence fixes the problem. Solar cells made from self-repairing semiconductors should last much longer than ones made with conventional materials, such as silicon, which accumulate damage. Nobody yet knows just how long such cells could survive, but at least one simulation suggests they could keep on working for hundreds of years. “It could well provide the stable, radiation-hard power supply for long-term space missions,” says Robert Tomlinson, a materials scientist at the University of Salford in Manchester. “Once it gets up there, it seems to last forever.” Until now, Cahen says, solar cell researchers have viewed the stability of CIGS as “black magic”. Now that the mechanism is understood, he expects the field to move forward quickly. At least one company, Siemens, markets CIGS solar cells. Franz Karg, a physicist at Siemens Solar in Munich, says that these cells already generate electricity more efficiently than other thin-film solar products. He’s intrigued by Cahen’s findings, and agrees that understanding the self-repair mechanism could encourage the development of even better semiconductors. Researchers can design new semiconductors in the same family, he says, by swapping copper and silver; indium, gallium and aluminium; or selenium and sulphur. Karg remains cautious, however. Cahen’s claims are “very bold”, he says,