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Focal-piShaper in Photovoltaics
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Lasers become more and more popular in production of various solar cells finding application in such technologies like:
- Edge Isolation,
- Vias Drilling,
- Patterning in Thin-Film cells (P1, P2 and P3 structuring),
- Edge Delete in Thin-Film cells,
- Marking,
and bringing increasing the productivity, quality and other features in production process.
Performance of above mentioned laser technologies can be seriously improved by applying the Laser Beam Shaping technique, for example, transformation of a beam intensity profile from Gaussian to so called flattop (uniform) distribution. This optical transformation helps to improve a trench profile in sense of steeper walls and reaching flat bottom, reduce drastically the HAZ (heat affected zone) and increase the productivity of material processing due to more efficient usage of the laser energy, see the details here.
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Just this transformation is realized by the refractive beam shapers Focal-piShaper (F-piShaper) - intended to work with lasers of different wavelengths and create flattop, donut and other intensity distributions for beams focused by a diffraction limited lens to spots below 100-200 micron.
The group of F-piShaper models is a part of a family of refractive beam shapers realizing so called field mapping optical approach and having the trade name piShaper. |
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Intensity profiles of focused beams under various F-piShaper settings
(Courtesy of Altechna, Lithuania) |
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| Input beam diameter 6 mm |
Input beam diameter 4.2 mm |
Animated presentation of intensity profile behaviour in zone of focal plane of a diffraction limited lens can be seen by clicking on the corresponding picture.
The operational principle presumes applying of a focusing lens after the F-piShaper. There can be a lens of any type: an F-theta lens, any kind of telecentric lens or focusing lens.
The most important feature of the lens is that it has to be diffraction limited one, in other words, it shouldn’t implement any wave aberration over whole working field. This is an essential condition for proper operation of the F-piShaper.
Effect of applying an F-piShaper in laser technologies of manufacturing the solar cells is illustrated on below pictures showing results of scribing of CIGS thin-film solar cell with a picosecond laser, wavelength 1064 nm, 100 kHz, M2 about 1.2.
This laser scribing corresponds to P3 structuring step when top layers of ZnO and CI(G)S to be removed and the bottom layer of Mo (molybdenum) to be opened; in the best case the Mo layer to become cleaned without damaging. |
Laser scribing of CIGS thin-film solar cell with a picosecond laser
(Courtesy of Erwin Steiger Laserservice, Germany)
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with Gaussian beam
Features:
- irregular trench edges,
- wide HAZ,
- the bottom Mo layer is partially damaged.
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with F-piShaper 9_1064
Features:
- even trench edges,
- steep walls,
- almost without HAZ,
- the bottom Mo layer is cleaned and almost untouched.
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Laser scribing with F-piShaper 9_1064
Variable pulse energy – increasing from left to right.
Features:
- by variable pulse energy the trench width is
almost invariable,
- optimum conditions are achieved for the second
from the right side scribe, where:
- even trench edges,
- highly reduced Heat Affected Zone,
- the bottom Mo layer is cleaned and
almost untouched.
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 - Leaflet - Focal-piShaper in Photovoltaics |
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