High-Throughput Ion-Implantation for Low-Cost High-Efficiency Silicon Solar Cells

This paper presents the use of ion-implantation for high-volume manufacturing of silicon solar cells. Ion-implantation provides a unique opportunity to obtain grid-parity because it simplifies the fabrication of advanced cell structures. It is shown in production that a streamlined ion-implantation process with homogeneous phosphorus doped emitter can raise the efficiency of 239 cm2 p-base Cz cells by 0.8% absolute, from 18.3% to 19.1%, while reducing the process sequence by one step relative to traditional POCl3 process. Average production cell efficiency is about 18.6% with maximum exceeding 19%. Several advanced cell structures were fabricated in R&D using ion-implantation and screen printed contacts. The advanced p-base structure with ion implanted selective emitter and local Al-BSF resulted in an efficiency of 19.6%. In addition, three different n-base cell structures were fabricated using boron (B) and phosphorus (P) implantation followed by in-situ front and back passivation during the implant anneal: the n-base cell with B emitter, passivated P-BSF with local contact and full metal back gave 19.2% efficiency, the implanted n-base bifacial cell was 19% efficient, and the n-base back junction cell with B emitter in the rear and P front surface field resulted in 19% efficiency.