Copyright 2009 Society of Photo-Optical Instrumentation Engineers. This paper was published in Proc. SPIE 7201-41, published online in March 2009 and is made available as an electronic reprint with permission of SPIE. One print or electronic copy may be made for personal use only. Systematic or multiple reproductions, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modifications of the content of the paper are prohibited. Effects of pulse duration on the ns-laser pulse induced removal of thin film materials used in photovoltaics Jim Bovatsek* a , Ashwini Tamhankar a , Raj Patel a , Nadezhda M. Bulgakova b , Jörn Bonse c a Newport Corp., Spectra-Physics Lasers Division North America, 1335 Terra Bella Ave, Mountain View, CA 94043, USA b Institute of Thermophysics SB RAS, Lavrentyev ave. 1, 630090 Novosibirsk, Russia c Newport Spectra-Physics GmbH, Ruhlsdorfer Strasse 95, 14532 Stahnsdorf, Germany ABSTRACT The removal of thin films widely used in photovoltaics as (transparent) electrodes (e.g. SnO 2 , 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. Keywords: thin film photovoltaics, solar cell, laser scribing, P1, P2, P3, nanosecond pulse, thresholds 1. INTRODUCTION Recent years have seen tremendous growth in emerging market economies throughout the world. The resulting rapid growth in resource consumption has driven the cost of energy to unprecedented levels. Accompanying this increased cost was increased interest in alternative energy sources such as photovoltaic (“PV”) devices. And with every surge in the price of oil or gas, there was a corresponding surge in the financial viability of such alternatives. While recently the rate of global economic growth has waned, and the cost of energy has retreated accordingly, interest in solar cell technology remains strong. This is providing a source of continued demand for various support industries such as laser and laser-based system manufacturing. The role of lasers in solar cell device fabrication continues to expand, with processes such as cutting, drilling, scribing, sintering, and annealing all being explored. For the highly-efficient crystalline silicon-based devices (“c- Si”), lasers are most commonly used for edge isolation scribing; but there is also a fast-growing application space with the increased fabrication of more exotic solar cells, such as “emitter wrap through” (via drilling) and buried contact (scribing) devices. 1 An increasingly popular alternative to c-Si solar cells is thin film photovoltaic (TFPV) device technology, for which the most important laser process is laser thin film removal (“laser scribing”) for electrical isolation of the individual segments of a monolithically integrated serial connection of solar cells. This process involves the irradiation of a glass panel with a tightly-focused laser beam, thus resulting in the removal of one or more layers of thin film from