Ion implantation as a potential alternative for the formation of Front Surface Fields for IBC silicon solar cells

Interdigitated back contacted cells (IBC) constitute an excellent option for the achievement of high-efficiency on silicon material. The effective implementation of an electrical field on the front side, also called Front Surface Field (FSF) is beneficial for this cell concept. It contributes to the reduction of the recombination and the enhancement of the lateral conductivity, improving the cell efficiency. The ideal FSF would push the minority carriers away, while restricting the Auger-recombination-active region to a minimal depth. In addition, too high doping leads to increased absorption in a highly-recombinative region, due to bandgap narrowing. Therefore, a trade-off should be achieved in an n-type IBC solar cell by the combination of a highly-doped n⁺ surface with a shallow doping profile. Such a profile can be manufactured by ion beam implantation. The experience gathered from CMOS processing enables excellent profile engineering, with independent control over the peak surface doping concentration and the doping depth even for high sheet resistances. Process and device modeling are presented on this paper. These have been used to estimate a range of interesting processing conditions for the use of ion implantation to the formation of FSF for IBC cells.