Competitive solar cell manufacturing requires production of a high precision component at the lowest possible price. Coherent provides laser technologies that achieve this goal by simplifying and speeding several solar cell fabrication steps, including various front side rear side processes, PSG laser doping, edge isolation and via hole drilling.
Laser process tools enable ultra-narrow c-Si solar cell line scribing
for edge isolation while minimizing sub-surface damages such as
Laser process tools for solar cell Edge Isolation all feature AVIA lasers; currently the dominant laser source for c-Si UV-laser Edge Isolation, with over 90% market share. Within laser Edge Isolation, a high-speed scanner directs UV or green nanosecond laser pulses around the perimeter of cells, scribing narrow grooves between the finger grid and the cell edges. The use of short-wavelength laser output enables ultra-narrow scribe lines (<30 μm), reduced ‘dead’ area around the trenches, and minimized sub-surface laser damage. Sub-surface damage – a negative outcome of using long wavelength IR lasers – can include changes to minority carrier lifetimes and bulk microcracking.
Coherent lasers enable highly precise scribing and doping processes for c-Si selective emitter formation.
Selective Emitters hold perhaps the greatest promise for efficiency enhancement within c-Si solar cell production. Laser-based tools have various roles within the different schemes already implemented or which form the basis of tomorrow’s high-volume production lines. Laser scribing (with short-wavelength nanosecond AVIA lasers) is performed at the front-end of Laser Grooved Buried Contact (LGBC) cells. Laser-assisted Dopant-Diffusion (either using the residual PSG layer or pre-deposited impurities) enables direct formation of strongly phosphorous doped regions. Here the short pulsewidths and fast (quasi-CW) pulsing from Paladin laser-based tools are ideal for production environments. Laser ‘doping’ can also be performed simultaneously with groove scribing or Dielectric Ablation.
Lasers and laser process tools enable highest precision c-Si ablation with minimized sub-surface bulk damage.
IOS tools for Edge Isolation all feature AVIA lasers; currently the dominant laser source for c-Si UV-laser Edge Isolation, with over 90% market share.Within laser Edge Isolation, a high-speed scanner directs UV or green nanosecond laser pulses around the perimeter of cells, scribing narrow grooves between the finger grid and the cell edges. The use of short-wavelength laser output enables ultra-narrow scribe lines (<30 μm), reduced ‘dead’ area around the trenches, and minimized sub-surface laser damage. Sub-surface damage – a negative outcome of using long wavelength IR lasers – can include changes to minority carrier lifetimes and bulk mAlso known as Selective Removal, Dielectric Ablation involves ablating thin layers of SiNx or SiO2 included on the cell surfaces to increase surface passivation while further assisting light transmission (front) or reflection (rear). Laser-based tools can ablate fine lines or holes with micron precision, while reducing sub-surface bulk damage to levels not affected by subsequent downstream process steps. Dielectric Ablation is a prerequisite for diffusion or plating mask formation/openings – both strong candidates for next-generation highefficiency cells. Key laser specifications include both short-wavelengths and short pulsewidths; factors which promote the AVIA, Talisker, and Paladin lasers.crocracking.
Coherent lasers are ideal for thin-film panel production due to their excellent pulse-to-pulse stability, accurate beam positioning on the panels, and a combination of short pulsewidth and high repetition rates greater than 100 kHz.
Thin-Film panels are actually comprised of a large number of thin ‘cells’ - or strips - that are interconnected to allow low-voltages to be added up in series across the panel, while keeping the current generated from the panel at a low level of a few amps. Dividing up these panels into cells involves the use of lasers to ‘pattern’ the layers during the Thin-Film deposition stages. Lasers have been the preferred technology for Thin-Film Patterning from the inception of Thin-Film production over ten years ago. As a result, this application for lasers within the Solar industry represents the area where lasers are most commonly used and have the highest visibility levels.
Each of the common Thin-Film absorber-types (a:Si, CIGS, Cd:Te) requires three Patterning stages (termed P1, P2, and P3). While a range of different materials is found across Thin-Film manufacturing, the Patterning steps are most typically performed with relatively low-power (up to 20W) short-ns-pulsewidth diode-pumped solid-state lasers, either at 1064, 532, or 355 nm. The choice of wavelength is typically due to the absorption properties of the materials used. Decreasing the pulsewidths can provide cleaner selective material removal: increasing the repetition rates can increase the process time on larger panel sizes.
AVIA based process tools enable highly reliable and precise c-Si wrap through processes.
Laser based tools can also be configured for ‘Wrap-Through’. This includes both Emitter and Metal Wrap-Through schemes. Here conductive pathways (via’s) are drilled through c-Si cells to allow contacts to be located at the rear of the cells; busbars for MWT and both fingers/busbars for EWT. With a ten-year heritage in drilling Through Silicon Via’s (TSV’s) within the semiconductor industry, the AVIA laser-based laser process tools provide ideal platforms here. Finally, various short-wavelength lasers provide the basis of front surface mask hole openings for etch-barriers, used in new concepts to texture the surfaces of multi-crystalline cells.
Risk factors: Except for the historical information contained here, many of the matters discussed in this Web site are forward-looking statements, based on expectations at the time they were made, that involve risks and uncertainties that could cause our results to differ materially from those expressed or implied by such statements. These risks are detailed in the “Factors That May Affect Future Results” section of our latest 10-K or 10-Q filing. Coherent assumes no obligation to update these forward-looking statements.