Efficiency record for laser-processed solar cells
by Christoph Hammerschmidt, EE Times Europe
05/25/2009 5:03 PM
Munich, Germany, 25 May 2009
Source: EETimes
http://eetimes.eu/germany/217600808
A team of researchers at the Stuttgart university has achieved an efficiency record for laser-processed solar cells based on crystalline silicon. The manufacturing process is fit for industrial volume production, the research group claims. The postgraduate research group led by Jürgen Köhler managed to produce crystalline silicon solar cells with an efficiency of 19 percent. Hitherto, this technology was limited to 16 percent. In the normal solar cell manufacturing, the pn junction is achieved in a high-temperature process in a diffusion furnace. The Stuttgart research group however used a pulsed laser beam instead in order to achieve the doping.
In the process developed by the group, a very thin phosphor layer is applied to the surface of a p-type silicon wafer. In the next process step, a very short laser pulse of only 1 nanosecond heats up the silicon surface to about 2.000 degrees Celsius. Since the pulse is so short, the heating effect applies only to a depth of less than a micron. During this process, the phosphor amalgamates with the then liquid silicon and the phosphor atoms are built into the silicon crystals, creating a pn junction.
According to the research team, the process achieves defect-free pn junctions if the laser exposition is focused on a very small strip of only about five microns. Since the entire exposition process is taking less than 100 microseconds, it is possible to process relatively large areas within a short time, the group said. According to the researchers, currently more than 90 percent of the world’s annual production volume of about €50 billion (about $67.5 billion) is allotted to crystalline silicon.