Evaluating the impact of current-generation screen-printed Ag paste on Si solar cell emitter saturation current density

Current-generation screen-printed (SP) Ag pastes have shown capability to contact lightly doped Si solar cell emitters displaying low saturation current density (J
_0e
) with high fill factor (FF). However, we have observed that higher firing temperatures are needed to achieve low resistance Ag contact, which may degrade J
_0e
and result in lower open circuit voltage (V
_OC
). Higher firing temperatures have also resulted in rear SP Al film blistering. In order to decouple the effects of front and rear contact formation on cell performance, we present data on the impact of SP Ag contacts on n+ phosphorus (P) emitter J
_0e
for a range of doping densities and firing temperatures. Using a range of Ag coverage areas (A
_metal
) we extract the J
_0e
under SP Ag (Joe, me
_ta
i)· We observe that the change in J
_0e
as a function of A
_metal
(dJ
₀
JdA
_meta
j) increases as firing temperature increases, indicating increasing J
_0e
,
_metal
. Calculated V
_OC
loss at A
_metal
= 7%, a typical coverage for SP Ag contacts, cannot fully account for experimental V
_OC
loss, and Al back surface field (Al-BSF) degradation due to high temperature firing was found to dominate V
_OC
losses.