Wet chemical poly-Si(n) wrap-around removal for TOPCon solar cells

• Published in: EPJ Photovoltaics Vol. 15; p. 9
• Main Authors: Krieg, Katrin, Mack, Sebastian, Vollmer, Jan, Dannenberg, Tobias, Brunner, Damian, Zimmer, Martin
• Format: Journal Article
• Language: English
• Published: EDP Sciences 2024
• Subjects: batch cluster etching; ex-situ; in-situ; inline etching; wet chemical
• ISSN: 2105-0716; 2105-0716
• DOI: 10.1051/epjpv/2024002

This work gives an overview on different technological solutions for polysilicon removal in industrial tunnel oxide passivated contact (i-TOPCon) n -type silicon solar cell fabrication. The removal of parasitically deposited poly-Si layers on the front and the edges is a mandatory requirement for a low reverse bias junction leakage current ( I rev ). A polysilicon removal study on wafer level shows (i) that the efficient removal of the surface oxide layer before poly-Si etching is crucial to achieve short etching times and (ii) that an additive in the KOH solution enhances etching selectivity between poly-Si and silicon oxide surfaces. To evaluate the impact on device level, TOPCon cells have been fabricated in parallel using in-situ n-doped PECVD and LPCVD layers, as well as ex-situ LPCVD poly-Si layers, with another variation of poly-Si removal processes, namely wet chemical inline, wet chemical batch cluster and atmospheric dry etching (ADE). Our results show that a two-minute inline polysilicon removal in hot KOH meets the I rev qualification in case of as deposited in-situ doped layers, whereas for ex-situ doped layers a batch process with a five-minute KOH etching time is needed. LPCVD poly-Si cells show efficiencies above 23%, PECVD poly-Si cells with a batch cluster poly-Si removal process up to 23.4%.