Novel Process for Screen-Printed Selective Area Front Polysilicon Contacts for TOPCon Cells Using Laser Oxidation

The efficiency potential of double-side tunnel oxide passivated contact (DS-TOPCon) solar cells is limited by parasitic absorption in the front poly-Si layer, despite excellent passivation and high
V_OC
. The use of patterned poly-Si only under the front metal grid lines can significantly reduce the parasitic absorption loss without sacrificing voltage. In this work, we demonstrate a simple, manufacturing-friendly method of patterning the front poly-Si using a nanosecond UV (355 nm) laser. We found that with laser powers
$ \geq $
3 W at a 400 mm/s scan speed, an estimated 1–4 nm thick stoichiometric SiO
₂
layer was grown on TOPCon. This served as a mask for KOH-etching of 200 nm poly-Si, allowing for patterning of poly-Si fingers required for selective TOPCon. While laser powers above 3 W caused substantial deterioration in passivation quality, the resulting damage in
J
₀
was largely recovered by subsequent PECVD SiN
_x
deposition. At 3 W, the full area
J
₀
was found to be 36.8 fA·cm
⁻²
. This translates to 1.68 fA·cm
⁻²
for 4.48% coverage from the wing area of the polyfinger lines (100 lines–100
$\mu \text{m}$
wide and 30
$\mu \text{m}$
metal) contributing to a total front
J
₀
of ∼10 fA·cm
⁻²
, well suited for 25% efficient solar cells.