Boron LCP local back surface fields for high efficiency silicon solar cells

This work shows the possibility to use local laser chemical processing (LCP) boron dopings to create local back surface fields (LBSF) in a high efficiency p-type silicon solar cell structure. In order to create boron local back surface fields with LCP an alkaline aqueous boron solution was used. Our recent work shows the potential of this doping source to create local dopings with a surface concentration of about 10²⁰ cm^-3 and a doping depth of up to 1.3 μm. For the first time the successful application of boron LCP as LBSF for high efficiency solar cells is shown. The processed LCP-PERL (passivated emitter and rear locally diffused) solar cells show a maximum cell efficiency of η = 20.9% and an absolute cell efficiency benefit of Δη = 0.3-0.4%abs. in comparison to the reference cells with undoped local rear contacts processed with water-LCP. The presented solar cells show the best cell efficiencies ever achieved with LCP dopings. For this study different LCP-parameters were varied such as the contact geometry (line openings and openings formed with a cascade of overlapping LCP dots) and the pitch of the rear side contact structure. The results show that the LCP boron doping process allows the fabrication of industrial feasible local back surface field structures with a line contact design for high efficiency p-type silicon solar cells.