Laser Applications for Photovoltaics Crystalline and Thin Film Technologies

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1 LASERS & MATERIAL PROCESSING I OPTICAL SYSTEMS I INDUSTRIAL METROLOGY I TRAFFIC SOLUTIONS I DEFENSE & CIVIL SYSTEMS Laser Applications for Photovoltaics Crystalline and Thin Film Technologies Back contact solar cell (MWT technology) Fraunhofer - Institut für Solare Energiesysteme (ISE)

2 Crystalline Solar Cells Laser Applications front contact emitter MWT / EWT wrap through contacts (-) metal coating (+) SiN coating (AR coating, passivation) n doping pn junction p-type Si wafer passivation layer backside contacts Metal / Emitter Wrap Through (MWT / EWT) up to 20,000 holes / second hole diameter µm before etching, 3-4 pulses / hole Preferred lasers: JenLas disk IR50 JenLas disk IR70 screen printed front contacts (-) emitter LFC laser fired contacts metal coating (+) SiN coating (AR coating, passivation) n doping pn junction p-type Si wafer passivation layer backside contact Laser Fired Contacts ( LFC ) up to 25,000 contacts / second ( PVD-Al ) up to 15,000 contacts / second ( SP-Al ) contact dimension µm, 1 pulse / contact Preferred lasers: JenLas disk IR50 JenLas disk IR70 JenLas disk IR70E screen printed front contacts (-) emitter SiN coating (AR coating, passivation) n doping pn junction p-type Si wafer passivation layer backside contact SiN / SiO dielectric layer opening up to 100,000 contact spots / second ablation diameter µm, 1 pulse / contact Preferred laser: JenLas D2.fs SiN contact opening metal coating (+) Further laser processes in crystalline photovoltaics edge isolation preferred lasers: JenLas fiber ns 10 70, JenLas disk IR50 / 70 wafer marking preferred lasers: JenLas fiber ns 10 70, JenLas disk IR50 / 70 module marking preferred laser: JenLas fiber ns wafer reshaping, TLS technology preferred laser: JenLas fiber cw stringer / junction box soldering preferred laser: JenLas fiber cw

3 Thin Film Solar Cells Laser Applications In thin film photovoltaics, there is considerable variation in layer composition and substrates. Each of these combinations requires specific laser parameters. Therefore, the following is presented as an overview only. These are examples of typical thin film coatings on glass substrates. P1 P2 P3 backcontact (metal) a-si / CdTe TCO glass a-si / CdTe type solar cells coating sequence: glass, TCO, emitter, metal contact patterning ( P1 / P3 ) Preferred laser: JenLas fiber ns emitter patterning ( P2 ): under development CIGS type solar cells P1 P2 P3 TCO CIGS backcontact (metal) glass layer structure opposite to a-si / CdTe type contact patterning ( P1) Preferred laser: JenLas fiber ns emitter patterning ( P2, P3 ) Preferred laser: JenLas D2.fs Further laser processes in thin film photovoltaics module marking preferred laser: JenLas fiber ns junction box soldering preferred laser: JenLas fiber cw

4 Jenoptik Laser Sources for Photovoltaic Applications JenLas disk IR50/70 l JenLas disk 70E IR disk laser up to 65 W laser source tunable pulse length 30 2,000 ns up to 300 khz flexible pulse repetition rate up to 7 mj pulse energy JenLas D2.fs diode-pumped thin-disk femtosecond laser wavelength 1025 nm pulse length < 400 fs up to 500 khz pulse repetition rate average power 5 W, up to 40 µj JenLas fiber ns air-cooled nanosecond fiber lasers W IR laser source tunable pulse length ns up to 1 MHz pulse repetition rate up to 1.25 mj pulse energy JenLas fiber cw high power cw fiber lasers W IR laser source fundamental mode beam quality up to 100 khz modulation air cooled and water cooled versions

5 Laser Technologies for Photovoltaic Industry by Jenoptik Crystalline (c-si) based solar cells constitute roughly 80 % of the worldwide production of photovoltaic (PV) cells. Although standard PV cell structures are a mature technology, there are plenty of bright ideas to enhance solar cell efficiency and push it closer to the theoretical limits. New structures are now being implemented into mass production which require new laser sources: EWT / MWT technology brings the front contacts to the PV cell backside. EWT / MWT (Emitter / Metal Wrap Through) requires laser drilling technology. For this application, Jenoptik has developed JenLas disk IR50, a unique laser source with independent tuning of pulse duration, repetition rate and pulse energy. Up to 20,000 through-holes per second theoretically can be drilled by the power enhanced version JenLas disk IR70. Cell passivation by SiN/SiO coatings allows efficiency gain by reduction of recombination losses. This technology requires a high-speed selective passivation opening with minimized impact of heat to the cell. For this application, Jenoptik offers a femtosecond laser source JenLas D2.fs, which can generate up to 100,000 contact openings per second in the passivation layer. Laser Fired Contacts (LFC) is an alternative technology for backside contacting by punctual melting ( firing ) of the metallisation through the passivation layer. Because different methods for metallisation are used, laser pulse length must be tuned to paste composition and layer thickness. For screen-printed metallisation 1 pulse per contact point with a rate of 15 khz using JenLas disk IR70 has been demonstrated. For LFC at PVD metallisation JenLas disk IR70E has been used with a rate of more than 25,000 point contacts per second. There are other process steps at wafer and module level, which Jenoptik offers laser technology for. A listing is given in the brochure. Cost reduction and efficiency enhancement are also major goals for thin film PV module production. For ITO and Molybdenium ablation JenLas fiber ns laser can be used. CI(G)S emitters are very sensitive to temperature and thus structuring by scribing needle is used today. Non-thermal processing by our femtosecond laser JenLas D2.fs is a good choice for replacement of mechanical tools. In this brochure we give an overview of lasers for the photovoltaic industry offered by Jenoptik.

6 JENOPTIK I Lasers & Material Processing Lasers Business Unit JENOPTIK Laser GmbH Goeschwitzer Strasse Jena l Germany Phone Fax sales-laser.lm@jenoptik.com It is our policy to constantly improve the design and specifications. Accordingly, the details represented herein cannot be regarded as final and binding en