Boron-doped pecvd silicon oxides as diffusion sources for simplified high-efficiency solar cell fabrication

Abstract

We develop plasma-deposited boron-doped silicon oxide layers with multifunctional capabilities: Firstly, they are used as local diffusion sources for attaining low saturation current densities of J 0 = 84 fA/cm 2 at sheet resistances as low as 67 /□ and surface boron concentrations in the range of 4–710 19 cm ‐3 , suitable for efficient metallization. Secondly, they act as diffusion barriers against other dopants. Therefore a co-diffusion process consisting of a boron drive-in and a phosphorus diffusion in a POCl 3 furnace in only one high temperature step potentially allows to simplify the fabrication of high-efficiency n-type PERT cells. Process and device simulations indicate that a co-diffusion temperature near 900C and a co-diffusion time of about 20 minutes are optimum for reaching cell efficiencies near 21%.