MATERIALS
There is only one type of nanosecond source that
References
hits the mark here: the Excimer laser. Which
indeed makes the nanosecond-vs-picosecond
i D. Fork et al., “Solar cell production using non-contact patterning and direct-write
debate all the more interesting! A comparison of
metallization,” European Patent EP1833099A2, filed January, 2007.
ii N. Posthuma et al., “Current and future metallization challenges and solutions for crystalline
process windows and fully amortized per-wafer
cell manufacturing,” Photovoltaic International, 3, 2009.
production costs will determine which laser type iii A. Knorz et al., “Progress in selective laser ablation of dielectric layers,” 22nd EUPVSEC,
will emerge as the industry favourite.
Milan, 2007.
iv K. Neckermann et al., “Local structuring of dielectric layers on silicon for improved solar
cell metallization,” 22nd EUPVSEC, Milan, 2007.
Several laser types have emerged as candidates
v S. Glunz et al., “Progress in advanced metallization technology at Fraunhofer ISE,” 33rd
for dielectric ablation. For minimised surface and
IEEE PVSC, San Diego, 2008.
bulk damage, picosecond lasers (either at 532 or
vi F. Colville, “Laser scribing exposed: the role of laser-based tools in the solar industry,”
Photovoltaic International, 3, 2009.
355 nm) should provide cleanest ablation with
vii N. Posthuma et al., “Development of high efficiency FZ silicon solar cells by application of
minimized sub-surface effects
4
: “the depth of the P the i-PERC concept,” 23rd EUPVSEC, Valencia, 2008.
profile increases proportionally to the laser
viii A. Gröhe et al., “Laser processes for the industrial production of high efficiency silicon
wavelength for locally opened structures using the
solar cells,” 22nd EUPVSEC, Milan, 2007.
ix P. Engelhart et al., “Laser processing for back-contacted silicon solar cells,” ICALEO LMC,
optimized laser parameters.
Paper M703, 2006.
x F. Colville et al., “Existing and emerging laser applications within PV manufacturing,”
SEM images demonstrated the complete or partial
Photovoltaic International, 1, 2008.
xi A. Knorz et al., “Selective laser ablation of SiNx layers on textured surfaces for low
surface melting when nanosecond lasers were
temperature front side metallization,” Prog. Photovolt. Res. Appl., 17, 127, 2009.
employed.” This suggests picosecond lasers as xii B. Xu et al., “Front-side metallization of crystalline silicon solar cells using selectively laser
ideal sources for either SiNx or stack removal with
drilled vias,” submitted to 34th IEEE PVSC, 2009.
underlying dopant regions, as confirmed by
xiii S. Correia et al., “Selective laser ablation of dielectric layers,” 22nd EUPVSEC, Milan 2007.
xiv V. Rana et al., “Investigations into selective removal of silicon nitride using laser for
Rana
14
: “by optimizing the process condition for
crystalline silicon solar cells,” 23rd EUPVSEC, Valencia, 2008.
picosecond pulse ablation, the deleterious effects xv P. Engelhart et al., “Laser ablation of SiO2 for locally contacted Si solar cells with ultra-
[using nanosecond lasers] on the substrate are
short pulses,” Prog. Photovolt. Res. Appl., 15, 521, 2007.
xvi F. Book et al., “Two diffusion step selective emitter: comparison of mask opening by laser
avoided.” In a recent study by Book
16
: “the
or etching paste,” 23rd EUPVSEC, Valencia, 2008.
[nanosecond] laser with a wavelength of 355 nm xvii A. Esturo- Breton et al., “Laser doping for crystalline silicon solar cell emitters,” 20th
was used to ablate the SiNx. The laser also melts
EUPVSEC, Barcelona, 2005.
the underlying silicon. Therefore, a damage
xviii B. Tjahjono et al., “High efficiency solar cell structures through the use of laser doping,”
22nd EUPVSEC, Milan, 2007.
etching is necessary.”
25
1 New metallization schemes generally includes two parts: a contact (silicide producing)
For rear side stack removal, nanosecond lasers
material deposited into the openings, followed by a highly conductive metal deposited on the
www
become strong candidates (with further relaxed
contact material.
2 Pulses even shorter than picoseconds are used widely, from ‘femtosecond’ lasers.
.solar
tolerances if bulk damage is annealed out).
Industrial-grade variants are limited to very low energy and power, ruling them out of solar
Optimization is ongoing here, first to show proof-of-
adoption. Further, operating with short femtosecond pulsewidths can introduce un4 of 11 -pv-management.com
principle for R&D / pilot-line implementation,
i D. Fork et al., “Solar cell production using non-contact patterning and direct-write
followed by tooling specification where production
metallization,” European Patent EP1833099A2, filed January, 2007.
throughput and ROI become decisive factors. ii N. Posthuma et al., “Current and future metallization challenges and solutions for crystalline
cell manufacturing,” Photovoltaic International, 3, 2009.
Conclusions
iii A. Knorz et al., “Progress in selective laser ablation of dielectric layers,” 22nd EUPVSEC,
Milan, 2007.
Correct choice of laser parameters is vital for
iv K. Neckermann et al., “Local structuring of dielectric layers on silicon for improved solar
successful implementation of laser ablated cell metallization,” 22nd EUPVSEC, Milan, 2007.
Issue II 2009
dielectric layers within next generation, high
v S. Glunz et al., “Progress in advanced metallization technology at Fraunhofer ISE,” 33rd
IEEE PVSC, San Diego, 2008.
efficiency concepts. Choosing the correct lasers
vi F. Colville, “Laser scribing exposed: the role of laser-based tools in the solar industry,”
with short wavelengths and short pulsewidths will Photovoltaic International, 3, 2009.
ensure that both damage (surface and bulk) and
vii N. Posthuma et al., “Development of high efficiency FZ silicon solar cells by application of
material modification can be avoided in teh
the i-PERC concept,” 23rd EUPVSEC, Valencia, 2008.
viii A. Gröhe et al., “Laser processes for the industrial production of high efficiency silicon
manufacturing process.
solar cells,” 22nd EUPVSEC, Milan, 2007.
ix P. Engelhart et al., “Laser processing for back-contacted silicon solar cells,” ICALEO LMC,
New industrial-grade lasers are available to meet
Paper M703, 2006.
this challenge for new pilot production lines. In
x F. Colville et al., “Existing and emerging laser applications within PV manufacturing,”
Photovoltaic International, 1, 2008.
future, the subsequent – or simultaneous –
xi A. Knorz et al., “Selective laser ablation of SiNx layers on textured surfaces for low
Selective Emitter diffusion (dopant within the
temperature front side metallization,” Prog. Photovolt. Res. Appl., 17, 127, 2009.
paste
1
, or discrete phosphorous-containing layer
xii B. Xu et al., “Front-side metallization of crystalline silicon solar cells using selectively laser
drilled vias,” submitted to 34th IEEE PVSC, 2009.
activated thermally via laser-induced
xiii S. Correia et al., “Selective laser ablation of dielectric layers,” 22nd EUPVSEC, Milan,
heating/melting
17,18
) may become easier to realize 2007.
for enhanced efficiencies.
xiv V. Rana et al., “Investigations into selective removal of silicon nitride using laser for
crystalline silicon solar cells,” 23rd EUPVSEC, Valencia, 2008.
xv P. Engelhart et al., “Laser ablation of SiO2 for locally contacted Si solar cells with ultra-
Further studies are necessary to compare ns-vs-ps
short pulses,” Prog. Photovolt. Res. Appl., 15, 521, 2007.
laser types, different UV wavelengths, and novel xvi F. Book et al., “Two diffusion step selective emitter: comparison of mask opening by laser
beam shaping arrangements, to identify the most
or etching paste,” 23rd EUPVSEC, Valencia, 2008.
xvii A. Esturo- Breton et al., “Laser doping for crystalline silicon solar cell emitters,” 20th
appropriate laser-based tool with the maximum
EUPVSEC, Barcelona, 2005.
ROI for cell producers. xviii B. Tjahjono et al., “High efficiency solar cell structures through the use of laser doping,”
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