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, is not fully understood yet. 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 suggests that stress due to thermal expansion is likely responsible for SiOx film fracture. Carrier transport mechanism of poly-Si/SiOx/Si junction was numerically investigated, revealing that tunneling charge-carrier transport competes with direct transport through pinholes. Moreover, a detailed current-recombination analysis in conjunction with predictions of device efficiencies was provide, providing a specific technical route to promote device efficiencies to 27%.