Study of the surface recombination velocity for ultraviolet and visible laser-fired contacts applied to silicon heterojunction solar cells

Abstract

In this study, we investigate the effect of the laser-firing process on the back surface passivation of p-type silicon heterojunction solar cells. For that purpose, two different nanosecond laser sources radiating at ultraviolet (UV) (355 nm) and visible (532 nm) wavelengths are employed. First, we optimize the laser-firing process in terms of the electrical resistance of locally diffused point contacts. Specific contact resistance values as low as 0.91 and 0.57 m Omega center dot cm(2) are achieved for the visible and ultraviolet laser sources, respectively. In addition, the impact of the laser-firing process on the rear surface passivation is studied by analyzing the internal-quantum-efficiency curves of complete devices. Low surface recombination velocities in the range of 300 cm/s are obtained for the ultraviolet laser with a 1% fraction of contacted area. This value increases to about 700 cm/s for the visible laser, which indicates a significantly higher recombination at the contacted area. The best heterojunction solar cells with rear laser-fired contacts are obtained for the ultraviolet laser and reached a 17.5% conversion efficiency.