Contact Formation and Recombination at Screen-Printed Local Aluminum-Alloyed Silicon Solar Cell Base Contacts

We study recombination properties and the formation of base contacts, which are realized by local laser ablation of a dielectric stack and the subsequent full-area screen printing of an Al paste. Based on charge-carrier lifetime measurements using the camera-based calibration-free dynamic infrared lifetime mapping technique, we determine contact reverse saturation current densities as low as
$J_{0, {\rm cont}} = \hbox{9} \times \hbox{10}^{2}\ \hbox{fA/cm}^{2}$
on 1.5-
$\Omega\hbox{cm}\ p$
-type float-zone silicon (FZ-Si) and
$J_{0, { \rm cont}} = \hbox{2} \times \hbox{10}^{4}\ \hbox{fA/cm}^{2}$
on 200-
$\Omega\hbox{cm}\ p$
-type FZ-Si. Scanning electron microscopy images reveal that the thickness of the highly Al-doped
$(\hbox{Al-}p^{+})$
layer considerably depends on the contact size and the contact layout (e.g., point or line contacts). Based on this finding, we show that
$\hbox{Al-}p^{+}$
layer thickness
$W_{{\rm Al}-p+}$
significantly affects the contact recombination. As a result, we show which local contact geometry is most appropriate for the lowest contact recombination employing local Al-alloyed contacts.