Dramatically lower prices for raw silicon (Si) have reduced the cost of solar power modules (panels). For total power system cost to continue to fall, however, new methods are required to produce high efficiency silicon solar cells that minimize material costs and processing complexity. Researchers at Fraunhofer Institute for Solar Energy recently demonstrated a method for high-efficiency silicon that may do just this.
More than 90% of the solar market employs silicon solar cells, the vast majority of which are crystalline-silicon-based. Though solar power systems are far cheaper today than ever before, the total balance-of-system cost (packaging, installation, transportation, etc) must be minimized for consumer prices to continue falling. With cheaper cells, the fraction of the total cost shifts to the other components which tend to scale with cell area: a sheet of glass that protects the cells in a panel has a cost proportional to the area of the panel, regardless of what cells are beneath the glass. These area-proportional costs favor cells with higher conversion efficiency, as they can produce the same power with less area and fewer panels. Of course, higher efficiency cells tend to be more expensive to produce and require more complex processing. Producing nearly perfect silicon crystal wafers with front and rear surface layers that properly take advantage of this high-quality material at a low cost is the frontier for silicon cell development.
All solar cells consist of a diode (a junction between two differently-doped regions of silicon) and metal contacts to extract current and power; techniques for forming these contacts on the surface, however, have major consequences for cell performance. Simple formation of large areas of metal contact is easy and fast but compromises cell efficiency. Alternatively, some of the most advanced schemes preserve high performance, but require advanced production techniques with fine features. Research out of the Faunhofer Institute for Solar Energy (ISE) suggests new techniques could balance the two. The new process from ISE uses an ultra-thin layer of oxide that protects the surface of the solar cell, yet allows current to escape through a process called “tunneling” – a phenomenon that is only accurately described through quantum mechanics. Using this process, researchers formed a very simple metal contact that didn’t require the expensive features of other designs.
With the cost of silicon falling, the push for high-efficiency low-cost cell designs could help to minimize all of the costs of the solar power system. With better fabrication techniques and larger production scale, new high-efficiency silicon cells could be the future of solar power.
F. Feldmann, M. Bivour, C. Reichel, M. Hermle, S. W. Glunz, New method for contacting high-efficiency silicon solar cells adds to growing evidence of industry shift. Solar Energy Materials and Solar Cells, 120, 270-274, (2014). DOI: 10.1016/j.solmat.2013.09.017