An improved process for making solar cells could allow manufacturers to cut the amount of silicon needed in half. Since silicon can account for about three-quarters of the cost of conventional solar cells, this could significantly lower the price of solar power. The technique can reduce the amount of other materials used and improve solar-cell performance.
The process uses ink-jet printing to make electrical connections within a solar cell, replacing the existing screen-printing process. Because the ink-jet method is more precise, it can use less material for these connections. Also, because the printheads don’t make contact with the silicon, the method works with thinner silicon wafers. The process uses an ink-jet printer built by iTi Solar, based in Boulder, CO, that was originally designed for printing electronics, such as the contacts on touch screens.
The National Renewable Energy Laboratory (NREL), in Golden, CO, which helped direct the design of the device, is now starting to produce solar-cell prototypes using the technology. Since the ink-jet printer can be dropped into existing solar-cell manufacturing lines, it could be used in commercial production within a year, estimates Maikel van Hest, a scientist at NREL.
One of the first applications could be in the manufacture of silicon solar cells, the most common type of solar cell sold today. Silicon absorbs light and converts it into electrons, and then an array of silver lines printed on the silicon collects these electrons, creating an electrical current. In conventional manufacturing, these silver lines are printed using screen printing. The silver ink used in the new process is much more conductive than the silver paste used in screen printing, and ink-jet printing is more precise. As a result, much thinner lines can be printed–35 to 40 micrometers wide, compared with 100 to 125 micrometers wide with screen printing, van Hest says. Using less silver saves money. It also improves the performance of the solar cell since the thinner lines shade less of the active material.