A new breed of quantum dots (QDs) could enable multilayer solar cells that capture more of the sun’s energy. Natcore Technology Inc. said scientists in the laboratories of co-founder Dr. Andrew Barron, who is also a professor at Rice University, have successfully formed a heterojunction solar cell using germanium QDs on an ordinary n-type silicon wafer. Individual germanium quantum dots were coated with silicon dioxide (silica), doped to make them p-type, and then deposited, using Natcore's liquid phase deposition (LPD) process, on a commercial-grade silicon wafer. The LPD process was developed at Rice and is licensed to Natcore. QD solar cells have the potential to capture solar energy more efficiently than other cells available commercially today. Their advantage lies in their tunability, that is, the careful control of their size to absorb energy from a specific spectrum of light. The portion of the spectrum not captured passes to the next layer below, where it can then be captured by another QD cell with a different absorption band or even another type of cell. Such multijunction or tandem cells with two or more could capture much more of the solar spectrum than traditional silicon cells. “To our knowledge, no one else has been able to successfully dope and arrange silicon or germanium quantum dots into layers using a process such as Natcore’s, which appears to be ideal for mass production,” said Natcore Co-Founder and Chief Technology Officer Dr. Dennis Flood. Tandem solar cells are used in space applications. The major issue preventing their broad use in terrestrial applications has been the need to use exotic semiconducting materials for the upper layers, according to Natcore. Natcore said its new cell is an important step toward a cell in which quantum dots are used to form both the p-type and n-type materials. Once this next step is achieved, it will open the door to potential ultra-high-efficiency, multijunction solar cells, the company said. For more information, visit www.natcoresolar.com.