Environmental Engineering Reference
In-Depth Information
Figure 9.4 Survey [112] of energy gaps and
band-edge energies of semiconductors and
oxides of use in solar cells and water splitters.
Note that the reduction energy level of water,
taken as zero on hydrogen electrode energy
scale of electrochemistry, is about 4.5 eV below
the vacuum energy. On the right are shown
energy levels for some additional reduction/
oxidation reactions in water solution.
Figure 9.5 Proposal [112] for inexpensive thin-
film tandem cell for water splitting. In its
realization, the two cells are stacked, just as in
Figure 9.1. The downward sloping arrow in the
center of this figure represents the
transparent
ohmic contact
connecting the two cells in
Figure 9.1. The
dye-sensitized TiO
2
cell on the
right is as described in connection with Figures
6.16
6.18, and the 1.6 eV arrow shown here
corresponds to the dye absorption energy rather
than the titania band gap.
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