Band bending photo potential

The development of photocathode materials for either single- or dual-absorber cells has also received considerable attention [80, 101, 102]. Thermodynamic equilibrium dictates that p-type semiconductors will exhibit upward band bending when in contact with a liquid electrolyte. This behaviour is the opposite to that of n-type semiconductors described previously, and will result in the movement of photogenerated electrons towards the semiconductor-electrolyte interface while the holes are driven into the bulk of the electrode, towards the electrical back contact. At the surface, provided that the energy carried by the electrons is sufficient, H2 is evolved. As discussed previously, one of the electronic properties of metal oxides that makes them suitable for water photo-oxidation purposes is the O 2p character of the valence electrons, which places the VB edge at potentials... 

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