Uygun, BerkayBerkayUygunKluska, SvenSvenKluskaPolzin, Jana-IsabelleJana-IsabellePolzinSchube, JörgJörgSchubeJahn, MikeMikeJahnKrieg, KatrinKatrinKriegTuran, RaşitRaşitTuranNasser, Hisham A.Hisham A.Nasser2025-03-262025-03-262025https://publica.fraunhofer.de/handle/publica/48583410.1002/pip.39012-s2.0-85218173243In this work, we demonstrate the formation of local boron-doped, SiOₓ/p + poly-Si structures using wet chemical etching by direct printing of boron-ink. FlexTrail printing uses a very hollow (orders of μm for diameter) glass capillary tube filled with boron ink for printing onto silicon substrate. This process represents a mask-free approach for the formation of local TOPCon structures, enabling high-efficiency tunnel oxide passivating contact (TOPCon) solar cells. The factors influencing etch-back selectivity between intrinsic and boron-doped poly-Si were thoroughly investigated. It was determined that pre-treatment with diluted HF (1 wt%) prior to poly-Si removal in a KOH solution is the most critical step to achieve optimal etch selectivity. This treatment effectively removes the native oxide on intrinsic poly-Si while preserving the boron silicate glass (BSG) layer on p + poly-Si, facilitating the selective removal of intrinsic poly-Si and the formation of p + TOPCon structures. Line widths ranging from 24.0 to 100.5 μm on planar surfaces and 40.0-86.0 μm on textured surfaces were achieved. FlexTrail printing allows for significantly lower (and higher) feature sizes, but its fine-line potential was not fully exploited here due to alignment challenges during post-processing. Test structures with a line grid of local TOPCon structures exhibited a maximum open-circuit voltage (𝑖VOC of 720 mV and a lowest saturation current density (𝐽0𝑆𝐸) of ~90-120 fA/cm2. The developed local p + poly-Si will be integrated into high-efficiency TOPCon solar cells, where p + poly-Si will be strategically placed under the metal contact, in the near future.enfalseFlexTrailLocal TOPConSelective Etch Back of Poly-SiSelective TOPConTOPConjournal article