Effects of pulse duration on the ns-laser pulse induced removal of thin film materials used in photovoltaics

The removal of thin films widely used in photovoltaics as (transparent) electrodes (e.g. SnO2, molybdenum) or solar absorber (e.g. amorphous silicon) materials is studied experimentally using multi-kHz diode-pumped solid state lasers in the visible and infrared spectral region. The film processing (or what is commonly known as P1, P2, or P3 laser scribing) is performed through the film-supporting glass plate of several millimeter thickness by using a galvo laser scanner setup equipped with f-theta optics. The dependence of the film removal fluence threshold on the laser pulse duration (~8 ns to ~40 ns) is investigated systematically for two different laser wavelengths of 532 nm and 1064 nm. The laser-scribing of continuous lines suitable for thin-film solar cell production is demonstrated successfully at scribe speeds on the order of meters per second. The experimental results are discussed on the basis of laser ablation models considering optical, geometrical, and thermal material properties and are additionally supported by numerical simulations.