Role of TiO₂ Surface Passivation on Improving the Performance of p-InP Photocathodes

The role of TiO 2 thin films deposited by atomic layer deposition on p-InP photocathodes used for solar hydrogen generation was examined. It was found that, in addition to its previously reported corrosion protection role, the large valence band offset between TiO 2 and InP creates an energy barrier for holes reaching the surface. Also, the conduction band of TiO 2 is well-aligned with that of InP. The combination of these two effects creates an electron-selective contact with low interface recombination. Under simulated solar illumination in HClO 4 aqueous electrolyte, an onset potential of >800 mV vs RHE was achieved, which is the highest yet reported for an InP photocathode.