Why Pulse Duration Matters in Photovoltaics

In the manufacture of thin-film photovoltaic (TFPV) solar panels, Q-switched diode-pumped solid-state (DPSS) lasers are routinely used for “laser scribing” – the selective removal of thin-film materials. These lasers are available at various wavelengths (266–1064nm), output powers (0.5–34W), repetition rates (up to 500KHz) and pulse durations (<10 to greater than 100ns). Developing the ideal laser scribe process – that is, one that removes only the desired material leaving the adjacent material unaffected – can be a challenge. In a non-ideal scribe process, not only can there be leftover material, but also high ridges can form along the scribe line. Additionally, the supportive glass substrate can develop micro-cracks that can then cause lift-off of the thin-film material. Because these unwanted ridges and burrs interfere with subsequent thin-film layers, these non-uniformities can lead to electrical shorts that reduce TFPV efficiencies and yields. This article addresses the various ways in which pulse duration affects the laser scribe process – specifically thin-film removal thresholds, scribe quality and substrate quality. It is shown that laser systems with shorter pulse durations will generally result in a laser scribe process that has lower material removal thresholds, cleaner scribes and minimal damage to glass substrates, ultimately leading to higher yields and lower overall manufacturing costs of TFPV panels.