Femtosecond-laser hyperdoping and texturing of silicon for photovoltaic applications

Abstract:

This dissertation explores strategies for improving photolvoltaic efficiency and reduc- ing cost using femtosecond-laser processing methods including surface texturing and hyperdoping. Our investigations focus on two aspects: 1) texturing the silicon sur- face to create efficient light-trapping for thin silicon solar cells, and 2) understanding the mechanism of hyperdoping to control the doping profiles for fabricating efficient intermediate band materials.> We first discuss the light-trapping properties in laser-textured silicon and its benefit to thin silicon heterojunction solar cells. We report a nearly 15% improvement in the short circuit current and device efficiency after surface texturing, which is attributed to the enhancement of absorption due to the formation of Lambertian surfaces. We next present studies on the hyperdoping mechanism using a pump-probe method. We measure in situ the change in surface reflectivity during hyperdoping and extract the dynamics of the melt front. Understanding the melt dynamics allows us to constrain the physical parameters in a numerical model, which we use to simulate the doping profile with a simplified classical picture. We then demonstrate the successful fabrication of homogeneously doped silicon by manipulating the hyperdoping process based on theoretically predicted design principles.