Passivating pinholes for large-area and high-efficiency silicon solar cells with tunnel oxide passivated contact

The tunnel oxide passivated contact (TOPCon) solar cell is poised to dominate silicon photovoltaics, yet the atomic-scale nature of pinholes-local disruptions in the SiO_x layer enabling direct conduction-remains unresolved despite its critical importance for device performance. Here, using spherical aberration-corrected transmission electron microscopy, the TOPCon interface is uncovered at the atomic level, revealing two distinct pinhole types: recombinational pinholes with oxygen-depleted Si-Si contacts, and previously unknown passivating pinholes that retain sufficient oxygen to passivate dangling bonds while enabling carrier tunneling. These passivating pinholes exhibit cross-sectional sizes of approximately 1.6 ± 0.2 nm × 1.4 ± 0.3 nm and an area density of 2×10¹² cm^-2. Fischer model analysis demonstrates that pinhole passivation, not geometry, governs device performance. Translating these insights, industrial large-area (333.3 cm²) TOPCon solar cells achieve certified efficiencies of 25.40% and open-circuit voltages of 738.7 mV. Our findings provide atomic-level insights into the TOPCon interface and offer direct guidance for fabricating high-efficiency solar cells.