Photocurrent enhancement in nanocoatings of cerium oxide and platinum on black silicon

Abstract

Black silicon is surface modification by reactive ion etching that creates a forest of silicon micro-spikes and increases surface area of the sample. When the spikes’ height exceed an optical wavelength, light is trapped on the surface through multiple pathway scattering, increasing the optical absorption of visible and near infrared radiation. Cerium oxide (CeO 2 ) is believed to have good photoactivity, and finds many applications including photoelectrolysis. However, the large band gap limits the efficiency of the water splitting process. We suggest black silicon surfaces as substrates for CeO 2 sputter coating to increase photon-material interaction. An additional catalytic layer of platinum is deposited to create highly energetic electrons as a result of plasmonic resonance and enhances incident photon to current efficiency (IPCE). The difference of surface current for laser on and off condition is found to be 32 times higher in a nanolayered coated black silicon sample as compared to flat silicon. The resistance of flat silicon substrate was 11 Ω for laser-off state, decreasing to 9 Ω when the laser was turned on. On the other hand, the black silicon substrate sample had a higher resistance of 70 Ω in dark which decreased to 1.5 Ω for laser on state.