Effects of Surface Passivation on Trap States, Band Bending, and Photoinduced Charge Transfer in P3HT/TiO2 Hybrid Inverse Opals

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.