Fine line Al printing on narrow point contact opening for front side metallization

Aluminum (Al) screen-printed narrow fingers on textured passivated emitter and rear totally diffused (n-PERT) front junction Si solar cells are applied and investigated. Commercial Al paste is screen-printed on symmetric test structures with different Local Contact Opening (LCO) designs by varying the dot-to-dot distances and finger widths. Strong dependency of the metal-silicon saturation current density (J0-met) is found for the considered geometries. Narrow Al grid metallization induced emitter recombination current density can be decreased by optimizing the dot-dot distance. Best results of our test matrix were determined for an 80 µm dot-dot pitch, realizing J0-met values down to 649 fA/cm2 when using narrow fingers of 65 µm compared with the J0-met of 1100 fA/cm2 identified for a commercial Ag/Al paste. For dot-to-dot distances below 40 µm, common pattern of bifacial p-type PERC, fingers with widths exceeding 120 µm are needed to realize J0-met values below 400 fA/cm2. Additionally, the shape and size of the Al-Si alloy and p++ doping layer depth after firing are strongly affected by the combination of dot-to-dot distances and screen-printed finger widths.