Chemistry Reference
In-Depth Information
corresponding metal electrode or the naked
p-
Si electrode. Conversion from solar
energy to chemical energy with a relatively large exchange current can be constructed
using Pt-deposited silicon electrode.
847
A silicon electrode with a small amount of deposited noble metals such as Pt does
not behave as a buried junction and the photoelectrode properties are still determined
by contact of the electrolyte, not the metal.
812
The photovoltaic response of the Pt-
deposited silicon electrode is due to the incomplete coverage of the surface by Pt so
that the interface energetics remains dominated by the contact of the semiconductor
surface with the electrolyte. The mechanism of the hydrogen reduction processes
involves first photoexcitation of electron-hole pairs followed by charging of the small
Pt islands with excited electrons. The charged Pt islands react with at a high rate.
According to Nakato
et al
.,
598,666,791,811
the effect of metal islands on the photo-
electrochemical properties of silicon electrode is a function of the relative dimension
of the metal islands, to the width of the space charge layer, As shown in Fig.
6.30b when the metal islands are as large as the space charge layer, the effective barrier
height at the metal/electrolyte interface, which determines the magnitude of photopo-
tential, is
semiconductor results in an effective barrier height at the metal/electrolyte interface,
On the other hand, when
the modulation of the field in the
which is almost equal to that at the semiconductor/electrolyte interface as shown in Fig.
6.30a. In this case, a large barrier height and large photo potential can thus be obtained.
The high effective barrier at the metal/semiconductor interface also means that the dark
saturation current is mainly determined by the minority carriers, similar to that without
metal deposition.
