Dielectric stack passivation on boron- and phosphorus-diffused surfaces and 20% efficient PERT cell on n-CZ silicon substrate

We present a surface passivation study of a B-diffused emitter and P-diffused back-surface field (BSF) of n-CZ Si substrates. The optimized passivation layers are subsequently incorporated into a 20%-efficient passivated emitter, rear totally-diffused (PERT) cell with V
_oc
of 672 mV. On the P-diffused, concentrated KOH-planarized BSF side, we compare different passivating plasma enhanced chemical vapor deposition (PECVD) SiN
_x
layer compositions. We demonstrate that a favorable combination of best passivation quality is achieved by a stack of thermal oxide grown at ~700°C, followed by a bilayer SiN
_x
, consisting of stoichiometric PECVD nitride and capped with Si-rich nitride, or H-dilution nitride. The stack results in surface passivation quality of J
_o
~ 17 fA/cm
²
for bilayer SiN
_x
and 14 fA/cm
²
for H-SiN
_x
on lightly P-doped BSF, and is very resistive to HF-containing wet etches. Surface preparation, deposition parameters, and post-growth annealing collaborate to define the effectiveness of the passivation. Their optimization is critical for integration of SiN
_x
:H into our high-efficiency solar cells. On the B-diffused textured emitter side, we use atomic layer deposition (ALD)-deposited Al
₂
O
₃
for surface passivation and low-temperature stoichiometric PECVD SiN
_x
for the anti-reflection coating. We discuss deposition conditions and thermal treatments for both ALD Al
₂
O
₃
and PECVD nitride that result in the optimized passivation resulting in J
_o
~ 52 fA/cm
²
and that prevent the blistering of the film.