Critical to both are tiny "microchannels" needed to interconnect a series of solar panels into an array capable of generating useable amounts of power, he said. Conventional "scribing" methods, which create the channels mechanically with a stylus, are slow and expensive and produce imperfect channels, impeding solar cells’ performance.
"Production costs of solar cells have been greatly reduced by making them out of thin films instead of wafers, but it is difficult to create high-quality microchannels in these thin films," Shin said. "The mechanical scribing methods in commercial use do not create high-quality, well-defined channels. Although laser scribing has been studied extensively, until now we haven’t been able to precisely control lasers to accurately create the microchannels to the exacting specifications required."
The researchers hope to increase efficiency while cutting cost significantly using an "ultrashort pulse laser" to create the microchannels in thin-film solar cells. "The efficiency of solar cells depends largely on how accurate your scribing of microchannels is," Shin said. "If they are made as accurately as possibly, efficiency goes up."
This image, taken with a scanning electron microscope, shows a microchannel that was created using an ultrafast-pulsing laser. Courtesy of Purdue University School of Mechanical Engineering image/Yung Shin.
Research results have shown that the fast-pulsing laser accurately formed microchannels with precise depths and sharp boundaries. The laser pulses last only a matter of picoseconds, or quadrillionths of a second. Because the pulses are so fleeting the laser does not cause heat damage to the thin film, removing material in precise patterns in a process called "cold ablation."
The process creates very clean microchannels on the surface of each layer, at very high speed of several meters per second, which is not possible with a mechanical scribe. This is very tricky because the laser must be precisely controlled so that it penetrates only one layer of the thin film at a time, and the layers are extremely thin. But the ultrafast pulsing laser offers very precise control of the depth, to about 10 to 20 nanometers.
The researchers plan to establish the scientific basis for the laser-ablation technique by the end of the three-year period. The work is funded through NSF Civil Mechanical and Manufacturing Innovation division.
Abstract on the research in this research is available at: https://www.purdue.edu/newsroom/research/2011/110308ShinSolar.html