Surface passivation of crystalline silicon by heat treatment in liquid water

A high photo-induced effective minority carrier lifetime τ_eff of crystalline silicon was achieved by simple heat treatment in liquid water. τ_eff was 2.8×10^-3 s for 15-Ωcm n-type crystalline silicon heat treated in liquid water at 120°C for 1.5 h. The τ_eff for the sample treated at 90°C increased from 1.0×10^-4 s (just after the treatment) to 1.7×10^-3 s by keeping the sample in the air atmosphere for 700 h. τ_eff maintained high values up to 1800 h. The metal-insulator-semiconductor type diodes were formed by forming Al and Au metals on the 0.7-nm-thick passivated layers. Rectified current characteristics were observed in the dark field because of the difference of the work function between Al and Au. Capacitance response with the bias voltage suggested low density of interface traps. Short circuit current density of 24.3 mA/cm² and open circuit voltage of 0.36 V were observed in the MIS-type solar cell under the light illumination of AM 1.5 at 100 mW/cm² to the rear surface.