Photodecomposition of Semiconductors

The most serious problem of all photoelectrochemical devices is the susceptibility of semiconductors in contact with electrolytes to photodecomposition. Such decomposition reactions are electrochemical redox processes in which the semiconductor is involved and they can occur already in the dark. The electronic charge carriers of the semiconductors are direct reaction partners in these processes. The next table gives a summary over a number of decomposition reactions in which either holes or electrons participate. Since these reactions are electrochemical processes their thermodynamics can be described in terms of redox potentials at which these processes would be in equilibrium. 

Anodic processes (p - type specimen or photodecomposition of n - type materials) 

The two following examples indicate how the redox potential can be derived by a combination of two electrode reactions, one of them being the reference electrode in aqueous solution the standard hydrogen electrode  

E is the Fermi level of the standard hydrogen electrode in this solvent. 

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Fig. 12. Corrosion diagram for samples of n- and p-type semiconductors s the equilibrium potential of the reaction of anodic photodecomposition of semiconductor with holes involved ( ° , is the equilibrium potential for a redox system /Red (/>cwr(n) and

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