An electron-selective SiCy/SiOx contact for Si solar cells made with fully industrial techniques

Abstract

We explored the use of inline plasma-enhanced chemical vapor deposition (PECVD) to make P-doped poly-Si/SiOx-type contact for Si solar cells utilizing only industrially viable techniques, especially Ag metallization via screen-printing of a commercial fire-through paste. For this we used a thick (97 nm), non-blistering PECVD Si-rich SiCy layer, called SRC2.0, to minimize the damage due to the aggressive metallization process. The blistering suppression in SRC2.0 is achieved through the incorporation of carbon in the film but comes at the expense of its electrical conductivity. Despite this, ohmic contact between Si and SRC2.0/SiOx could be formed by annealing at 925 degrees C and higher. Moreover, we discovered that SRC2.0 has a detrimental effect on surface passivation with a thin (1.6 nm) SiOx layer that is typically used with poly-Si. This is due to reduction of the passivating SiOx layer during high-temperature annealing by the high amount (15%) of C in SRC2.0. Using a slightly thicker (1.9 nm) SiOx layer mitigated this effect, and J(0) values of 10 fA/cm(2) and lower (4 fA/cm(2)), and 40 fA/cm(2) could be obtained in un- metallized and metallized regions, respectively. The best n-type Si solar cell with the SRC2.0/SiOx contact at the rear showed a very high short-circuit current density of 41.4 mA/cm(2) and a good open-circuit voltage of 688.4 mV. Its efficiency was, however, limited to 20.7%. This was due to the high specific contact resistance ((10-40) m Omega.cm(2)) of the SRC2.0/SiOx contact, which in turn limited the fill-factor of the device to 72.6%. Nevertheless, the trends suggest that better device results can be obtained by using higher thermal budget.