Study on Al metal paste contacting n+ doped Si surfaces for industrial solar cell application

In this work, we present a study on the contact formation of Al thick film metal paste to phosphorous doped n
⁺
Si surfaces. We were able to modify the contact resistance for the applied paste using atomised Al alloy particles as metal powder in the paste matrix by changing the peak doping of the Si substrate as well as by variations of the applied sintering profile. We found a specific contact resistance ρ
_c
below 3 mΩ · cm
²
at a peak phosphorous doping level of 2x 10
²⁰
cm
^-3
established with a belt furnace sintering process and a firing profile beyond 800°C peak temperature. Tests on lower (9×10
¹⁹
cm
^-3
) doped layers showed for symmetric SiN surface passivated devices with laser contact point opening (LCPO) on 0,6% of the wafer area a recovery of the implied V
_oc
after Al metallisation of about 5 mV compared to LCPO reference samples without metallisation. The results open up the possibility for Ag free screen printed contact designs on Si solar cells using Al thick film metallisation for both, n
⁺
and p
⁺
doping polarities.