Self Aligned Aluminum Selective Emitter for n-type Si Cells

We show a method for making a self-aligned selective emitter by annealing aluminum grid lines above the SiAl eutectic temperature, and study the recombination properties using lifetime measurements. The dark saturation current density at the metal contact (J
_0,metal
) is determined as a function of minority carrier density using photoconductive decay. After annealing at 600 °C, J
_0,metal
decreases from 1800 fA cm
^-2
to 500 fA cm
^-2
at an injection level of 1E15 cm
^-3
. This value of J
_0,metal
would correspond to a very low emitter recombination contribution of ~10 - 25 fA cm
^-2
for a front metal grid with area coverage of 2 - 5%. In addition, J
_0,metal
is found to be injection dependent. A low contact resistivity of ~0.1 mOhm cm
^-2
is obtained from transmission line measurement (TLM).