Passivation of silicon surfaces by oxygen radical followed by high pressure H2O vapor heat treatments and its application to solar cell fabrication

We report passivation on the silicon surfaces by combination of oxygen radical and high pressure H₂O vapor heat treatment. The top bear surface of 20 Ωcm n-type silicon substrates with the rear surface coated by 100 nm thermally grown SiO₂ layers were treated by oxygen radical generated from oxygen plasma via a metal mesh closing the plasma induced by 13.56 MHz radio frequency induction-coupled remote plasma with mixed gases of O₂ and Ar at 10 sccm, 1.0 Pa and at a power of 100 W. The samples were subsequently annealed with 1.3×10⁶ Pa H₂O vapor heat treatment at 260°C for 3 h. A high effective minority carrier lifetime of 1.1×10^-3 s was achieved in the case of 635 nm light illumination on the top surface in the case of the oxygen radical treatment for 3 min. Metal-insulator-semiconductor-type solar cells were formed by formation Al and Au metal strips with a gap length of 17 μm on the passivated surfaces. When airmass 1.5 at 100 mW/cm² were illuminated on the rear surface with 100 nm thermally grown SiO₂ layers, solar cell characteristics were observed by applying voltage between Al and Au electrodes. The open circuit voltage and efficiency were obtained as 0.51 V and 6.4 %.