Photovoltages and Stability Criteria

Based on (quasi-)thermodynamic considerations, it can be shown that the separation of the quasi-Fermi levels at the surface yields the maximum attainable 

The reactive semiconductor-electrolyte interface makes stability a major issue in photoelectrochemical solar energy conversion devices, and aspects of thermodynamic and kinetic stability are briefly reviewed here. Thermodynamic stability considerations are based on so-called decomposition levels [56, 57] that are determined by combining the decomposition reaction with the redox reaction of the reversible hydrogen reference electrode. The anodic and cathodic decomposition reactions of a compound semiconductor MX can be written for aqueous solutions as 

As an example, the light-induced anodic decomposition of CdS is discussed here which results in the formation of a passivating sulfur film according to CdS-t2h (hv) Cdjq -tS . In the derivation of the decomposition potentials, the hydrogen electrode serves as source or sink of electrons according to 

3) The calculation involves integration over the single wavelength profiles including diffusion and drift. 

The kinetics of the decomposition reactions such as Equations 2.25a-d involve individual reaction steps. For an anodic decomposition, for example, the individual decomposition levels are considered for the first two partial reactions  

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