Charge Transfer in Poly (3-Hexylthiophene) / Titanium Dioxide Inverse Opals: Effects of Surface Passivation and Donor Concentration

Hybrid photovoltaics are attractive because of their low cost and ability to be applied onto flexible substrates. However defect states can trap charges and are undesirable. We investigate TiO2 inverse opals treated with titanium tetrachloride (TiCl4) and subsequently coated with poly(3-hexylthiophene) (P3HT) to elucidate the effect of surface passivation on the photoinduced charge transfer and polaron dynamics. The chemical, physical and morphological properties were characterized using UV-vis spectroscopy, reflectance microscopy, X-ray diffraction, Raman spectroscopy and scanning electron microscopy. Passivation resulted in increased wall thickness of the inorganic framework and crystallite size. Photoinduced absorption spectroscopy showed enhanced polaron absorptions and reduced polaron lifetimes with increased titanium tetrachloride concentration and reduced concentration of the solution from which the P3HT is cast. The 3D structure presents an opportunity to study the charge transfer within a percolated network.