Improved laser edge isolation of crystalline silicon solar cells using a high power picosecond laser

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 leads to recasting 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. 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 of 7 ps and 20 ns and repetition rates of 400 kHz and 50 kHz respectively leading to a high processing speed. In this work a comparison of the shunt resistance (R_shunt) obtained by picosecond and nanosecond laser sources is done.