Codiffusion Sources and Barriers for the Assembly of Back-Contact Back-Junction Solar Cells

摘要

In this study, several diffusion sources are investigated, aiming at codiffusion for the fabrication of back-contact back-junction (BC-BJ) silicon solar cell. As a gaseous diffusion source, a POCl-diffusion process is investigated, and for solid diffusion sources, phosphorus- and boron-doped silicate glass (PSG and BSG) deposited by the means of plasma-enhanced chemical vapor deposition are considered. The n-doped areas diffused from a solid PSG layer allow for a precise adjustment of the sheet resistance in the range of 40–400 Ω/sq, along with a dark saturation current density of 55 fA/cm. Subsequently, boron diffusion from solid BSG layer leads to p-doped areas with high doping levels ( 50 Ω/sq). However, gaseous POCl diffusion in combination with solid boron diffusion from the BSG layer can only be successfully performed if the BSG layer is protected with an SiO layer. Furthermore, by adjusting the gas flows during POCl diffusion, n-doped areas with in the range of 150– 300 Ω/sq are achieved. The corresponding surfaces feature values of 30 fA/cm . The result of this study is a flexible codiffusion setup allowing for the efficient integration in advanced process chains of BC-BJ solar cells which results in the cell efficiencies well above above 20%.