Photon Energy and Redox Processes

It should be noted that these effects are generally not observed at potentials for redox couples located at potentials negative (n-type semiconductors) or positive (p-type semicoductors) of the flat band potential. In these cases, the majority carriers (electrons for n-type semicoductors, holes for p-type ones) tend to accumulate near the semiconductor/electrolyte interface and the semiconductor behavior approaches that of a metal electrode. 

Correlation between electrochemical and spectroscopic data usually focuses on the determination of band gap energy and the estimation of the position of upper edge of the valence band (HOMO energy) and the lower edge of the conduction band (LUMO energy). Formal electrode potentials are correlated to the vacuum level as previously indicated. In most cases, the corresponding energies, Fhomo  

FIGURE 11.8 Schematic representation of (a) n- and (b) p-type semiconductor in contact with an electrolyte solution containing an Ox/Red redox couple under irradiation of photons with energy larger than the band gap energy. 

---