New simplified methods for patterning the rear contact of RP-PERC high-efficiency solar cells

New processing schemes for fabricating the rear contact pattern of the PERC-structure (passivated emitter and rear cell) are demonstrated. Both, thermally-grown silicon oxide (SiO₂) and plasma-deposited silicon nitride (SiN_x) are used as the passivating rear layer. The first processing scheme utilizes plasma etching of the dielectric layer through a mask. The plasma process was optimized in order to reduce the damage in the silicon base of the cell. Efficiencies of 21.5% and 21.7% have been achieved for SiN_x and SiO₂ rear layers, respectively. The second approach uses a laser beam to remove the dielectric layer for the rear contact pattern. Efficiencies of 19.7% and 21.3% have been achieved for SiN_x and SiO₂ rear layers, respectively. Reference cells with the same front structure but conventionally processed rear (photo resist, wet-chemical etching) show only a slightly higher efficiency of 22.0% on cells with a SiO₂ passivation layer. This proves that both approaches have a very high potential