dye sensitized electron transfer in bandgap materials

In Gratzel cells, fluorescent dye molecules are excited by photons, and the electrons from the excited state of the dye are brought into
the conduction band of a semiconductor. A photocurrent is the result.
I assume, that when a metal is used instead of a semiconductor, there is no bandgap and the excited electron falls back immediately into a low energy state providing no photocurrent.
If an insulator is used instead of a semiconductor, would a photocurrent be possible (for example, if the excited electrons have high energy)?
Is it possible to think of the dye as a strong reducing agent, and the semiconductor acceptor as being oxidized when the electron is transferred to its high energetic conduction band?
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