Electronic structures of two types of TiO₂ electrodes: inverse opal and nanoparticulate cases

Abstract

We present a comparison between the electronic structures of inverse opal (IO) and nanoparticulate (NP)-TiO 2 electrodes. The electronic structure details were obtained from optical absorption, fluorescence, and valence band studies in order to clarify the nature of the higher photovoltaic performance observed in sensitized solar cells using IO-TiO 2 electrodes. We used photoacoustic (PA) and photoluminescence (PL) spectroscopy to characterize the optical absorption and fluorescence properties, respectively.Photoelectron yield (PY) spectroscopy was applied to characterize the position of the valence band maximum (VBM) of the IO-and NP-TiO 2 electrodes. The PA spectrum for IO-TiO 2 is different to that for NP-TiO 2 , indicating differences in the exciton-phonon interactions and the density of states in the conduction band. PL measurements showed that the curvature of the valence band structure of IO-TiO 2 is different to that of NP-TiO 2 . Also, PL measurements showed that the oxygen vacancy in IO-TiO 2 is different to that in NP-TiO 2 . Moreover, PY measurements showed VBM in IO-TiO 2 to be at a higher position than that in NP-TiO 2 , suggesting a correlation with the increased open circuit voltage (V oc ) in sensitized solar cells.

Boosting visible light harvesting and charge separation in surface modified TiO2 photonic crystal catalysts with CoOx nanoclusters

“…445, 490 and 530-560 nm, related to emission from shallow defect states, such as oxygen vacancies. 62,63 Surface modification of the PC films resulted in the marked drop of the near-band gap PL emission and the defect-induced PL peaks after the 1st CC cycle, supporting the interfacial charge transfer of UV photogenerated electrons to surface states introduced by CoO x nanoclusters. 22 The PL intensity continued decreasing with the CC cycles, though at a smaller extent for PC406 after the 2nd cycle ( Fig.…”

Visible Light Trapping against Charge Recombination in FeOx–TiO2 Photonic Crystal Photocatalysts

“…Charge recombination and the presence of defect states were explored by PL spectroscopy for the FeO x –PC260 films under 275 nm excitation, as shown in Figure 7 a. The PL spectrum of pristine PC260 showed a broadband at 380 nm arising from the near-band gap emission via indirect band-to-band transitions of anatase nanoparticles, accompanied by a much weaker shoulder at about 450 nm originating from shallow defect states due to oxygen vacancies [ 5 , 74 , 75 ]. Surface modification by FeO x nanoclusters resulted in the progressive decrease of near-band gap emission along with a red shift of its spectral position reaching 400 nm for FeO x –PC260-3rd.…”

Graphene Quantum Dot-TiO2 Photonic Crystal Films for Photocatalytic Applications

“…Charge separation was further investigated by PL spectroscopy for the GQD-PC261 and GQD-P25 films under 275 nm excitation, as shown in Figure 11 d. The PL spectra of the unmodified PC and P25 films showed a broad band at about 380 nm arising from the near-band gap PL emission of the titania nanocrystals with small variations between the single-anatase PC and anatase/rutile P25 films, accompanied by much weaker shoulders at λ > 400 nm originating from shallow defect states [ 65 , 66 ], though with no sign of GQD’s blue emission. Surface modification of the PC and P25 films by GQDs resulted in the decrease of PL intensity corroborating the reduced electron–hole recombination and most importantly, pointing to the interfacial transfer of UV photogenerated electrons from TiO 2 to GQDs that function as electron scavengers.…”