Maskless Patterning of Laser Activated p+ poly-Si Layers and the Fast Firing Stability of Patterned p+ poly-Si layers

Abstract

Advanced TOPCon solar cells with local p+ poly-Si/SiO₂ passivation stacks under the front metal contacts can be a future replacement for the current TOPCon baseline design. The local p+ poly-Si/SiO₂ layers eliminate the metal-induced recombination on the front side, and the local placement of these layers prevents high parasitic absorption losses. Laser activation of p+ poly-Si/SiO₂ layers provides an etch stop layer and allows for maskless patterning of these layers in alkaline solution. Patterning in this work refers to removing the poly-Si layer and texturing the substrate in the areas that are not laser-activated. In the laser activation step, the laser processing parameters must be carefully selected to entirely melt and activate the poly-Si layer without damaging the SiO₂ layer beneath. Since partially activated poly-Si layers are not fully etch resistant in alkaline solution, patterning step removes the partially activated poly-Si layer and lowers the passivation quality. Even though the fully activated and patterned p+ poly-Si/SiO₂ layers show similar passivation quality as non-patterned p+ poly-Si/SiO₂ layers before the fast firing step, the fast firing step degrades the passivation quality of the patterned samples. However, an additional re-hydrogenation step in the fast firing furnace can restore the passivation quality of the patterned samples. This fast and industrially feasible re-hydrogenation method ensures a good passivation quality of p+ poly-Si/SiO₂ layers in the final fabricated solar cell.