Microscale Contact Formation by Laser Enhanced Contact Optimization

Abstract

A technique to improve contacts of solar cells laser enhanced contact optimization (LECO) has been studied in terms of micro scale contact formation at industrial PERC solar cells. High-resolution diagnostics by focused ion beam techniques and scanning electron and transmission electron microscopy indicate the LECO-induced formation of microscopic contacts at the buried interface between the screen-printed silver finger and the silicon wafer. A large quantity of these micro contacts where found exclusively for LECO processed cells. Target preparation and three-dimension cross-section investigation reveal an interdiffusion of the Ag and Si material as the underlying root cause for improved local contact resistivity. We propose a descriptive model for local ohmic contact formation maintaining surface passivation.