Optimized aerosol jet printed silver contacts on lowly doped phosporous and boron emitters
For highly efficient silicon solar cells, lowly doped phosphorus or boron emitters are essential prerequisites to achieve sufficient surface passivation. However, contact formation to such lowly doped surfaces remains a challenge for traditional printing technologies. The question arises if such emitters can be contacted reliably applying advanced metallization inks. For this investigation, we manufactured lowly doped boron and phosphorus emitters with / < 1·1020 cm-3 onto silicon substrates with high pyramid texture. For metallization we used our optimized aerosol jet printing process and altered the ink deposition density from 6 to 23 g/m². On textured wafers the seed layer width remained < 40 mm in average with our own developed seed layer ink. For characterization purposes the lines were thickened with electro-plated silver. Contact resistivity measurements were performed to judge the suitability of this metallization scheme. It is shown that contact formation mainly depends on the firing temperature and less on the amount of deposited ink. Contact resistivities of 1-7 mO·cm² for the phosphorus and 6- 12 mO·cm² for the boron emitter could be achieved.