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 [SiO_x]/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 SiO_x film fracture. The carrier transport mechanism of the poly-Si/SiO_x/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%.