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
Abstract
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.