Recombination of photoexcited holes in anodic reactions

In photoexcited n-type semiconductor electrodes, photoexcited electron-hole pairs recombine in the electrodes in addition to the transfer of holes or electrons across the electrode interface. The recombination of photoexcited holes with electrons in the space charge layer requires a cathodic electron flow from the electrode interior towards the electrode interface. The current associated with the recombination of cathodic holes, im, in n-type electrodes, at which the interfadal reaction is in equilibrium, has already been given by Eqn. 8-70. Assuming that Eqn. 8-70 applies not only to equilibrium but also to non-equilibrium transfer reactions involving interfadal holes, we obtain Eqn. 10-43  

The current i flowing in photoexcited n-type semiconductor electrodes equals the sum of the photoexcited hole current i h, the limiting current of hole diffusion ip. itB, and the current of hole recombination inc as shown in Eqn. 10—44  

In the photostationary state, Eqn. 10—44 equals the transfer current of anodic holes across the electrode interface shown in Eqn. 10-39. 

As described in this section, the Fermi level bEp of a photoexcited n-type electrode with a transfer current, t, of anodic holes corresponds to a polarization potential bBCi) of the electrode whereas, the quasi-Fermi level of the photoexcited n-type electrode corresponds to a polarization potential pE(i) (= - pEp/e = - associated with the transfer current i of anodic holes at a p-type electrode 

Consequently, by measuring the polarization curves for the transfer reaction of anodic holes both at a photoexdted n-type electrode and at a dark p-type electrode of the same semiconductor, we obtain the relationship between the Fermi level of the electrode (polarization potential E) and the quasi-Fermi level of interfadal holes in the photoexcited n-type dectrode as a function of 

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