High efficiency selective emitter cells using patterned ion implantation

Abstract

AbstractIn this paper we present recent advances of the Varian patterned ion implantation selective emitter solar cell process, Solion Blue. Varian's ion implantation system, known as Solion, is currently deployed in manufacturing. This novel doping approach enables 1) simplification of the process flow by eliminating the non-value add steps such as PSG etch and junction isolation common to diffusion-based processes, 2) improved junction quality compared to diffusion processes through precise dopant control, and 3) improved surface passivation using a thermal oxide/silicon nitride ARC. Improvements in emitter quality, through oxide passivation and elimination of the “dead” layer associated with diffusion based processes, has enabled production of>18.5% efficiency solar cells with simplified processing. The Solion Blue process enables patterned doping using in situ masking, rendering manufacturing of a precise selective emitter with an additional cell efficiency boost. Here we report on the first in a series of optimizations of the ion implanted selective emitter cell process, focusing on assessing the impact of the metallization contact width. These results suggest that, unlike diffusion based selective emitter processes, in which the focus is minimization of the contact width, due to attendant higher surface recombination, the ion implant selective emitter architecture is relatively invariant with contact width, thus enabling a wider contact window. Good surface passivation, precision doping and simplified processing make a compelling case for patterned ion implantation as the preferred doping approach for selective emitter cells and other high efficiency cell architectures, including those that require patterned boron