Electrochemical potential shift, under illumination

Thus, Eq. (35) implies that a noticeable shift of the electrochemical potential level under photogeneration can only take place for minority carriers. For moderate illumination intensity, the shifts of the quasi-levels, F p, are proportional to the logarithm of the intensity as it increases, further growth of the shifts slows down due to enhancement of recombination processes. The ultimate shift of F p with increasing illumination intensity, so long as Eq. (35) (and a similar formula for a p-type semiconductor) is valid, is the edge of the corresponding band. 

Though processes occurring under photopassivation have not so far been understood in detail, they may be related with certainty (Izidinov, 1979) to the acceleration, under illumination, of one of the two conjugated reactions, which constitute the overall process of electrochemical corrosion. Depending on the initial state of corroding silicon, either the anodic (at the active surface) or the cathodic (at the passive surface) partial reaction is accelerated. This leads to the shift of the potential, and the system jumps over the maximum of the polarization curve from one stable state to the other. 

The onset potential for the freshly etched p-CdTe for the photo-electrochemical reduction of carbon dioxide is -0.76V NHE. When the electrode was cycled between -0.56 to -2.24V under illumination, the onset potential for the photocurrent shifts to less cathodic potentials and remains constant at -0.66V after about c. 20 minutes. When the electrode is potentiostated at -2.0V the photocurrent remained constant for about 24 hours. These results are reproducible and consistent with the published data. Surface analysis of the etched surface of p-CdTe using XPS and SEM showed only trace amounts of carbon and oxygen. 

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