SOLAR cells could become much more efficient with the discovery of a way to make a single photon liberate two electrons instead of one. Most solar cells are made of sheets of semiconductor. A photon hitting the material knocks just one electron out of the crystal structure, allowing a current to flow. If the photon has more energy than is required to do this, the excess is lost as heat.
But when a high-energy photon hits a semiconductor nanocrystal, the extra energy kicks out more electrons. 鈥淵ou absorb the same number of photons but can produce double the number of electrons. Sometimes we observe three electrons produced by a single photon,鈥� Victor Klimov, the team leader at the Los Alamos National Laboratory in New Mexico, told New 杏吧原创. Klimov and his colleague Richard Schaller noticed this effect when they aimed a laser at crystals of lead selenide less than 10 nanometres wide (Physical Review Letters, vol 92, p 186,601).
A solar cell that harnessed this effect could convert 60 per cent of sunlight into useable power because it would make better use of higher-energy blue and ultraviolet light. By contrast, the maximum theoretical efficiency of a conventional solar cell is only 44 per cent.
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