The Effect of SPA-SiO2 Tunnel Oxide Thickness for Metal-Insulator-Silicon Photoelectrochemical Cells

The photoelectrochemical properties of metal-insulator-silicon cells with varying SiO2 thickness are studied using slot-plane-antenna (SPA) growth. This method can produce ultrathin films with precise thickness at low temperatures. N-type silicon photoanodes and degenerately doped p-type silicon anodes are fabricated with SPA-SiO2, compared to devices with chemical-SiO2, and found to produce similar results to previous studies. The electrochemical performance of SPA-SiO2 oxides of varying thickness is measured and modeled in order to map the trend of performance with varying thickness. The modeled resistance of charge transfer in ferri/ferrocyanide is found to increase exponentially with SiO2 thickness in agreement with a quantum tunneling mechanism expected for a tunnel junction and notably different from previous behavior observed for ALD-TiO2/SiO2 anodes. These findings are set in context of the goal of fabricating devices optimized for both efficiency and long-term stability.