Improvement of Passivation Quality by Post-Crystallization Treatments with Different Methods for High Quality Tunnel Oxide Passivated Contact c-Si Solar Cells

We report a systematic study of the post-crystallization treatment effects on the passivation quality of tunnel oxide passivated contact (TOPCon) on n-type CZ c-Si wafers with different methods, including thermal annealing in forming gas, and moisture carried by nitrogen, as well as capping with atomic layer deposition (ALD) Al
₂
O
₃
and plasma-enhanced chemical vapor deposition (PECVD) SiN
_x
:H following a thermal annealing in nitrogen. We found that the annealing at a moderate temperature of ~450°C within a mixture of nitrogen and moisture is an effective way for improving the passivation quality, with which a high quality passivation with an implied open circuit voltage (iV
_oc
) of 729 mV is achieved. A hydrogen containing capping layer with ALD Al
₂
O
₃
on the poly-Si contact layer is found to be the most effective way for improving the passivation, with which an outstanding passivation quality with an iV
_oc
of 747 mV, effective life time (τ
_eff
) of 4.07 ms (Δn= 5.0×10
¹⁵
cm
^-3
), and single-side saturated recombination current density (J
₀
) of 1.9 fA/cm
²
is attainted. Using the optimized TOPCon passivation layer on solar grade CZ wafers, we achieved a solar cell efficiency of 22.2%.