Effects of Thermal Fluctuations on the Structure, Level Alignment, and Absorption Spectrum of Dye-Sensitized TiO₂: A Comparative Study of Catechol and Isonicotinic Acid on the Anatase (101) and Rutile (110) Surfaces

Abstract

The adsorption of catechol and isonicotinic acid on the TiO2 anatase (101) and rutile (110) surfaces has been studied by means of first-principles molecular dynamics simulations and time-dependent density functional calculations. Our results show that thermal fluctuations induce changes in the position of the molecular levels around the TiO2 valence band edge. For the anatase (101) surface, the alignment of the molecular levels with the TiO2 valence band edge has a significant effect on the absorption spectrum. For rutile (110), instead, the adsorption of catechol and isonicotinic acid induces only a minor sensitization. The sensitization of anatase (101) by catechol and isonicotinic acid can be enhanced by increasing the hybridization between the adsorbed dye and TiO2 states.

Two-step model for ultrafast interfacial electron transfer: limitations of Fermi’s golden rule revealed by quantum dynamics simulations

“…The LUMO of the adsorbate lies approximately 0.4 eV above the lower edge of the conduction band of the TiO 2 semiconductor, limiting the number of available states on TiO 2 capable of accepting electrons via IET. Previous computational studies of the pyCA–TiO 2 system performed at the DFT level of theory placed the LUMO of the carboxylic acid 0.19–0.53 eV relative to the TiO 2 anatase conduction band edge, 78 , 79 in agreement with our calculated values.…”

Optical Absorption Spectra and Excitons of Dye-Substrate Interfaces: Catechol on TiO2(110)

“…This is consistent with the red shift of the absorption spectrum calculated with PBE time dependent (TD)DFT in ref. 16 for catechol on rutile compared to anatase TiO 2 .…”

“…5 In such DSSCs, an electron is excited either to the lowest unoccupied molecular orbital (LUMO) of the dye and relaxes to the conduction band minimum (CBM) of the substrate (type-I DSSC), [6][7][8][9][10] or to the CBM directly (type-II DSSC). [11][12][13][14][15][16] For type-I DSSCs, the device's photovoltaic efficiency is determined by the dye's energy gap and the interfacial level alignment of the LUMO and the CBM, 10 while for type-II DSSCs, the device's photovoltaic efficiency is determined by the interfacial level alignment of the HOMO and the CBM. 14 To determine which process dominates, one must consider the optical absorption of the isolated dye, substrate, and their interface.…”

The Pros and Cons of Polydopamine-Sensitized Titanium Oxide for the Photoreduction of CO2

“…However, the CO 2 reduction performance of R@PDA-1 nm and B@PDA-1 nm is worse than the pure TiO 2 phases ( Figures S3 and S4). It might be due to the mismatch of the excited state of PDA with the CB edge of rutile and brookite [39][40][41].…”