Scribing of thin-film solar cells with picosecond and femtosecond lasers

Continuous growth of the thin-film solar technology market stimulates the development of versatile technologies for large-scale patterning of thin-film materials on rigid and flexible substrates, and laser technologies are a promising method to accomplish the scribing processes. In this study we compare picosecond and femtosecond pulse laser scribing for thin-film solar cells. For this we selected a Nd:YVO4 mode locked picosecond laser with the pulse duration of 10 ps and a Ti: sapphire laser with the pulse duration of 300 fs. We concentrated on so-called P3 step of laser scribing to expose the molybdenum back-contact. The visual quality of the scribes was controlled with optical and scanning electron microscopes. The conversion efficiency tests, LIT (lock-in thermography) and LBIC (laser-beam induced current) measurements were performed on the laser-scribed complete working solar cells of prefabrication stage. The damage-free exposure of molybdenum layer was possible in complex thin-film structure with both pulse durations. LIT and LBIC measurements did not show evidence of internal shunt formation near the scribed zone using lasers with both pulse durations. The efficiency tests confirmed an insignificantly higher solar cell performance after femtosecond laser scribing, although at both pulse durations marginal reduction in solar cell efficiency was observed.