Local p+ Poly-Si Passivating Contacts Realized by Direct FlexTrail Printing of Boron Ink and Selective Alkaline Etching for High Efficiency TOPCon Based Solar Cells

In this work, we demonstrate the formation of local boron doped, p+ SiO x/ poly-Si structures using wet chemical etching by direct printing of boron-ink FlexTrail printing. This process is a mask free approach for the formation of local TOPCon structures for high efficiency tunnel oxide passivated contact (TOPCon) solar cells. Factors affecting the etch back selectivity between intrinsic and boron doped poly-Si are studied. It is found that pre-treatment by diluted HF (1 wt%) before poly-Si removal by a KOH solution is the most crucial process to ensure etch selectivity. Etching the native oxide on intrinsic and keeping the boron silicate glass (BSG) layer on p+ poly-Si is the optimum condition for removing intrinsic poly-Si while having p+ TOPCon structure. Line widths in the range of of 86-100 µm and 24-40 µm were achieved on planar and textured surfaces, respectively. FlexTrail printing allows for significantly lower (and higher) feature sizes, but its fine-line potential wasn't fully exploited here for alignment reasons of post-processing. Test structures with a line grid of local TOPCon structures featured a maximum open circuit voltage ( iV OC) value of 720 mV and lowest saturation current density of local p+ SiO x/ poly-Si (J 0SE) ~ 90-120 fA/cm 2. The developed local p+ poly-Si will be integrated in high efficiency TOPCon solar cell where p+ poly-Si will be placed under the metal contact in the very near future.