Light-enhanced surface passivation of TiO ₂-coated silicon

Titanium dioxide is shown to afford good passivation to non-diffused silicon surfaces and boron-diffused surfaces after a low-temperature anneal. The passivation most likely owes to the significant levels of negative charge instilled in the films, and passivation is enhanced by illumination-advantageous for solar cells-indicating that a titanium dioxide photoreaction is at least partly responsible for the low surface recombination. We demonstrate a surface recombination velocity of less than 30 cm/s, on a 5-Ωcm n-type silicon, and an emitter saturation current density of 90 fA/cm ² on a 200-Ω/sq boron diffusion. If these titanium dioxide passivated boron-diffused surfaces were employed in a crystalline silicon solar cell, an open-circuit voltage as high as 685 mV could be achieved. Given that TiO ₂ has a high refractive index and was deposited with atmospheric pressure chemical vapour deposition, an inexpensive technique, it has the potential as a passivating antireflection coating for industrial boron-diffused silicon solar cells.