Hole-blocking crystalline-silicon/titanium-oxide heterojunction with very low interface recombination velocity

We demonstrate a hole-blocking crystalline-silicon/titanium-oxide heterojunction that can be fabricated by a modified MOCVD process at only 100 ^oC substrate temperature. Ultra thin layers of only 1-4 nm TiO₂ can be reliably deposited on silicon with no pinholes. Band alignment at the Si/TiO₂, experimentally determined using surface spectroscopy, confirms that Si/TiO₂ interface has a large barrier at the valence band, which blocks holes. The hole-blocking characteristics allow the Si/TiO₂ heterojunction solar cells to achieve power conversion efficiencies > 7%. Finally, the electrical quality of the Si/TiO₂ interface was characterized in terms of interface recombination velocity. We show that annealed Si/TiO₂ interfaces can achieve recombination velocities of ~ 200 cm/s.