Mechanistic studies of n-Si photoelectrodes have been conducted using aqueous and nonaqueous electrolytes. In contact with the CH3OH-dimethylferrocene (Me2Fc)+/0 electrolyte, the dark current and open-circuit voltage (Voc) were not dependent on acceptor concentration for [Me2Fc+] ≤ 0.010 M and were only weakly dependent on acceptor concentration for [Me2Fc+] ≥ 0.010 M. For [Me2Fc+] between 0.3 mM and 0.050 M, the temperature dependence of Voc indicated that bulk-diffusion/recombination was the rate-limiting recombination process. In all of these experiments, conventional Shockley diode theory provided an excellent description of the solid/liquid junction properties. In a related set of experiments, HF-etched n-Si photoelectrodes ((100)- and (111)-oriented samples) and n-Si samples that had been metalized by several different methods all showed passivation in contact with Fe(CN)6 3-/4- (aq) or Br2/Br- (aq) electrolytes. For several metalized Si samples, etches that had been reported to produce metal islands on the Si surface instead yielded Si surfaces free of metal. All Si samples that had been metalized by filament evaporation yielded I-V behavior in contact with the CH3OH-Me2Fc+/0 redox system that was characteristic of a pinned surface Fermi level, even for coverages of metal as low as 9 Å. This indicates that proposed metal-insulator-semiconductor junctions with anomalously high barrier heights are difficult to obtain by such metalization and etching methods.
|Number of pages||8|
|Journal||Journal of Physical Chemistry|
|Publication status||Published - 1991|
ASJC Scopus subject areas
- Physical and Theoretical Chemistry