Quantum dot technology could make solar panels more efficient

Science : Researchers at the US National Renewable Energy Laboratory (NREL) have created a new type of solar cell that captures some of the excess solar energy normally lost as heat, writes Robert Service for Science. When high-energy photons from the Sun hit a semiconducting material in a solar cell, they excite the semiconductor’s electrons from a static position so they can conduct. But the photons carry more energy than is needed, and the rest gets lost as heat. Several years ago, it was found that the high-energy photons can excite more than one electron if the semiconductor consists of nanometer-sized particles called quantum dots. The NREL group used the process, known as multiple exciton generation (MEG), in their quantum dot solar cell to achieve a 5% overall efficiency at converting light to electricity. That efficiency is still well below conventional silicon solar cells, which make better use of the full solar spectrum. But the device is the first to collect more electrical charges than the number of photons that struck the quantum dots—a convincing demonstration of MEG. The group’s results were published 16 December.