Product Code: ICAL09_M903

Improved Laser Edge Isolation of Crystalline Silicon Solar Cells using a High Power Picosecond Laser
Authors:
Oliver Haupt, Laser Zentrum Hannover e.V.; Hannover Germany
Viktor Schuetz, Laser Zentrum Hannover E.V.; Hannover Germany
Rainer Kling, Laser Zentrum Hannover E.V.; Hannover Germany
Henning Nagel, Schott Solar Ag; Alzenau Germany
Stefan Bagus, Schott Solar Ag; Alzenau Germany
Wilhelm Hefner, Schott Solar Ag; Alzenau Germany
Wilfried Schmidt, Schott Solar Ag; Alzenau Germany
Severin Massa, Trumpf Laser Gmbh & Co.Kg; Schramberg Germany
Uwe Stute, Trumpf Laser Gmbh & Co.Kg; Schramberg Germany
Thomas Schlenker, Manz Automation Ag; Reutlingen Germany
Presented at ICALEO 2009

Edge isolation of crystalline silicon solar cells can be done by laser scribing. The non-contact technique is perfectly suited for thin wafers and inline processing due to the brittleness of the crystalline silicon. Common laser sources are solid-state based and used in the second or third harmonic wavelength due to the short optical penetration depth in crystalline silicon. However, the pulse duration in the nanosecond range or longer leads to recast of molten or evaporated silicon and eventually to the diffusion of dopants deep into the bulk. As a result, the edge isolation is not perfect. New high-power picosecond laser sources are a promising alternative because they ablate material nearly without melting. In this work we compare the shunt resistance (Rshunt) obtained by picosecond and nanosecond laser sources. Isotextured multicrystalline (mc) Si solar cells featuring a double-side diffusion and screen-printed metallization were edge-isolated by means of the laser sources with pulse durations from 6 ps to 20 ns and repetition rates of 400 kHz/ 50 kHz leading to a high processing speed. The cells were characterised by illuminated current-voltage measurements, infrared camera imaging under reverse bias and optical microscopy. First investigations show a calculated increase in efficiency of 0.16 % absolute.