We report on the
synthesis and photophysical properties of a photocathode
consisting of a molecular bilayer structure self-assembled on p-type
NiO nanostructured films. The resulting photocathode and its nanostructured
indium–tin oxide analog absorb visible light and convert it
into injected holes with injection yields of ∼30%, measured
at the first observation time by nanosecond transient absorption spectroscopy,
and long-lived reducing equivalents that last for several milliseconds
without applied bias. An initial quantum yield of 15% was achieved
for photogeneration of the reduced dye on the p-NiO electrode. Nanosecond
transient absorption experiments and detailed analyses of the underlying
electron transfer steps demonstrate that the overall efficiency of
the cell is limited by hole injection and charge recombination processes.
Compared with the highly doped indium–tin oxide photocathode,
the NiO photocathode shows superior photoconversion efficiencies for
generating reducing equivalents and longer lifetimes of surface-bound
redox-separated states due to an inhibition toward charge recombination
with the external assembly
