Thin mc Si low cost solar cells with 15% efficiency

The firing-through SiN screen-printing process was adapted for thin mc Si wafers with a thickness of 180 μm. The optimization of this industrially compatible solar cell process resulted in a cell efficiency of 15.2% for a cell area of 10×10 cm² and an emitter with a sheet resistance of 35 Ω/sq. For cost saving and to avoid the bending of thin wafers with an entirely metallized rear side, the coverage of the rear side metallization was reduced. Three different local back contact processes were carried out: including a noncompensated rear side emitter, a back-to-back diffusion, and alternatively a diffusion barrier. All processes include rear side silicon nitride deposition followed by screen-printing a square pattern of lines with Al-paste to perform the back contacts. The reduction of the rear side SiN-layer thickness from 80 nm to 25 nm leads to a short-circuit current density enhancement of 0.7 mA/cm² and efficiencies up to 14.1%