MANUFACTURINGLASERS
variety of customer supplied substrates. JPSA’s patent pending beam delivery technology ensures uniform flat top beam exposure (Figures 7 and 8) with high beam utilization and efficiency for high throughput, high quality scribing.
JPSA has incorporated proprietary scribing methods in the PV-5000 thin-film solar panel scribing system (Figure 9). The scribing width is user adjustable down to 20 microns thus minimizing the “dead area” to less than 400 microns. The PV-5000 system offers scribing speeds up to 2 meters/sec, resulting in 30 seconds total process time for a Gen 5 solar panel of 1.2 meter by 0.6 meter size with 10 mm pitch between scribing lines.
Figure 9: JPSA PV- 5000 integrated scribing system for thin-film solar cell production
100 or more cells which are interconnected in series. A laser is used to scribe parallel lines across the full width of the panel. As shown in Figure 5, by alternating laser scribes with deposition steps, the cells are connected in series. These P1, P2, P3 laser scribes have different requirements and optimization needs to be performed for a successful production line.
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Typical DPSS lasers have a Gaussian beam distribution. Scribing by overlapping consecutive pulses which have non uniform energy distribution often leads to non optimized results (Figure 6). This can easily be understood by considering that the consecutive scribes cannot impact the underlying layers. Since energy density is a major parameter controlling scribe quality it follows that constant energy density on target is important to increase process window.
Also a circular spot projected on target leads to non uniform overlapping along the scanning direction. Despite strong evidence that a homogenous flat top beam leads to improved results still several laser system manufacturers use a Gaussian-like beam on target. JPSA has spent many years developing scribing techniques on a
Outlook
Photo-voltaic technologies are advancing rapidly as they strive for higher efficiency and lower manufacturing costs. These technologies undoubtedly have a bright future; however they also face considerable challenges to overcome.
Solar-cell manufacturing has been a demanding application for laser processing due to the requirement of both high- accuracy and cost- efficiency. This quest will be only fulfilled by optimized laser parameters specific to each application, as well as robust systems offering high-speed, reliability and consistency.
Large-scale high-quality production of solar cells/panels using lasers is already well established. In addition to the ongoing development of laser systems, new machining techniques and applications, improved beam delivery optical systems and enhanced knowledge of laser beam-material interactions will be required to sustain the progress of this green revolution.
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REFERENCES [1] Colville, F., “Laser scribing exposed: the role of laser-based tools in the solar industry”, Photovoltaics International, Ed.3, p.105 (2009).
[2] Mason, N., “High efficiency crystalline silicon PV cell manufacture: status and prospects”, PVSAT-5, Glyndwr, Wales (2009). [3] Beaucarne, G., “Silicon thin-film solar cells,” Advances in OptoElectronics, vol. 2007, Article ID 36970, 12 pages (2007). [4] Hecht, J., “The key to success is higher efficiency”, Laser Focus World, p. 39, March (2009). [5] Kyeong, D. et al, “Laser edge isolation for high-efficiency crystalline silicon solar cells“, Journal of the Korean Physical Society, Vol. 55, No.1, 124-128 (2009).
[6] Mai, T., Richerzhagen, B., “Laser microjet technology: fundamental study and highlight of its latest applications”, Proceedings of ALAC 2007, Burlington, MA, USA (2007).
[7] Pirozzi, L. et al, “Innovative applications of laser technology in photovoltaics”, Proceedings SPIE Conf. on Laser Applications in Microelectronic and Optoelectronic Manufacturing II, San Jose, CA, USA (1997).
[8] Dunsky, C., Colville, F., “Scribing thin-film solar panels”, Industrial Laser Solutions for Manufacturing, Pennwell, February (2008).
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