Dielectric Charge Tailoring in PECVD SiO${}_x$/SiN ${}_x$ Stacks and Application at the Rear of Al Local Back Surface Field Si Wafer Solar Cells

State-of-the-art surface passivation results are obtained on undiffused p-type commercial-grade Czochralski Si wafers with effective surface recombination velocity S
_eff
values of ~8 cm/s and implied open-circuit voltage iV
_oc
values of up to 715 mV with an industrially fired dielectric stack of silicon oxide and silicon nitride (SiO
_x
/SiN
_x
) deposited in an industrial inline plasma-enhanced chemical vapor deposition reactor. We are able to controllably vary the total positive charge density Q
_total
in the stack by more than one order of magnitude (10
¹¹
-10
¹²
cm
^-2
) with no impact on midgap interface state density D
_{it,m idgap}
(5 × 10
¹¹
eV
^-1
· cm
^-2
) by altering the deposition temperature of the SiO
_x
layer in the stack. We show experimentally that, for inversion conditions, S
_eff
scales with the inverse square of the charge density 1/Q
²
_total
, which is in good agreement with theory. Based on the measured injection-level-dependent minority carrier lifetimes and the total positive charge densities, it is shown that films with higher positive charge density have higher 1-sun Voc and fill factor (FF) potential. Large-area alloyed aluminum local back surface field solar cells confirmed this by showing higher conversion efficiency by 0.17% absolute due to improved cell V
_oc
and FF of the solar cells featuring a SiO
_x
/SiN
_x
stack with a higher Q
_total
.