Charge-carrier dynamics for silicon oxide tunneling junctions mediated by local pinholes

Tunnel oxide passivating contact (TOPCon) technology has attracted much attention in the crystalline silicon (c-Si) photovoltaic (PV) community due to overwhelming advantages for device efficiency and cost. However, fundamental device physics of the core structure of TOPCon (i.e., the polycrystalline silicon [poly-Si]/silicon oxide [SiOx]/c-Si junction), are not yet fully understood. Here, we conduct extensive experiments and simulations to clarify the underlying dynamics of the junction featuring local pinholes, including pinhole formation processes and charge-carrier transport mechanisms. The pinhole formation process is investigated by following the film dynamics, which suggest that stress due to thermal expansion is probably responsible for SiOx film fracture. The carrier transport mechanism of the poly-Si/SiOx/Si junction is numerically investigated, revealing that tunneling charge-carrier transport couples with direct transport through pinholes. Moreover, a detailed current-recombination analysis in conjunction with predictions of device efficiencies is demonstrated, providing a specific technical route to promote device efficiencies to 27%. [Display omitted] •Pinhole formation process is probed by thermal expansion model•Carrier transport through-tunneling and pinholes are theoretically confirmed•A systematic model to evaluate passivation and contact properties is established•The best devices show an average efficiency over 23.5% on the large-area wafers By combining experiments and simulations, Yang et al. reveal the formation process of pinholes and charge-carrier transport mechanisms of poly-Si/SiOx/c-Si contacts. This work may shed light on the underlying device physics of the poly-Si/SiOx/c-Si junctions and provides guidance on achieving high-efficiency TOPCon devices.