We
investigate the effect of a common TiO2 passivation
reagent, TiCl4, on the photoinduced charge transfer of
poly(3-hexylthiophene) (P3HT) to TiO2 in the inverse opal
structure. Treating the inorganic oxide framework with TiCl4 leads to an increase in the size of the TiO2 nanoparticles,
a thickening of the inverse opal framework, and a decrease in the
trap-state photoluminescence. These changes lead to different energy
alignments at the interface. In comparison to the unpassivated P3HT/TiO2 inverse opal, we measured a larger polaron yield, by as high
as ninefold, and significantly shorter and more uniformly distributed
polaron lifetimes in TiCl4-treated samples. We show that
downward band bending in the polymer can be circumvented by tuning
the trap states on the metal oxide using TiCl4, thereby
eliminating the energetic barrier for photoelectron injection from
the polymer to the metal oxide. The findings suggest a way to overcome
a potential factor that has plagued the performance of metal oxide–polymer
hybrid photovoltaics.
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