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 VOC. 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 ≥ 3 W at a 400 mm/s scan speed, an estimated 1-4 nm thick stoichiometric SiO2 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 J0 was largely recovered by subsequent PECVD SiNx deposition. At 3 W, the full area J0 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 μ m wide and 30 μ m metal) contributing to a total front J0 of ∼10 fA·cm-2, well suited for 25% efficient solar cells.