Development and Fabrication of High Efficiency N-Type Tunnel Oxide Passivated Silicon Solar Cells with APCVD, Ion Implanted, and BBr3 Boron Emitters
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Madani, Keeya
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Abstract
This thesis focuses on developing cost-effective, high efficiency (~23%) n-type silicon solar cells utilizing tunnel oxide passivated contacts (TOPCon) on rear and optimized boron-doped emitters on front of a n-type Si wafer. Incorporating an ultra-thin tunnel oxide capped with doped poly-Si significantly reduces minority carrier recombination in the doped and metallized regions, enhancing efficiency without increasing costs. This research involves solar cell modelling, design, fabrication, and characterization of commercial-ready n-TOPCon solar cells. It also covers fundamental silicon solar cell principles, characterization tools, and a literature review on technology trends. First, a technology roadmap was developed with Quokka 2 device modelling to improve the baseline n-type p+/n/n+ PERT cell efficiency from 20.5% to 23% through a combination of front side boron emitter optimization, development and integration of rear side n-TOPCon, and improved screen-printed metal contacts. Three different B diffusion technologies, including APCVD, ion implantation, and BBr3 were investigated, optimized, and integrated into cell processing.
Fabrication of large-area n-TOPCon cells resulted in 23.3% efficiency with BBr3 emitter followed by 22.7% for ion implantation and 22.2% for APCVD emitters. Detailed device characterization and modelling was performed on these cells to identify and quantify the loss mechanisms in these cells and a new technology roadmap is proposed to take n-TOPCon cell efficiencies to > 25% by using higher quality Si wafers, ultra-high sheet resistance emitters, and improved metallization techniques. The research successfully developed high efficiency (~23%) commercial-ready n-TOPCon cells, setting a foundation for making photovoltaics the cheapest electricity source.
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2025-04-16
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Dissertation