Novel Laser Oxidation for Screen-Printed Selective Area Front Poly-Silicon Contacts for TOPCon Cells

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 33 W at a 400 mm/s scan speed, a 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 poly-finger lines (100 lines-100 wide, 30 metal) contributing to a total front J0 of -10 fA.cm-2, well suited for 25% efficient solar cells.