Optical Absorption Spectra and Excitons of Dye-Substrate Interfaces: Catechol on TiO${}_2$(110)

Abstract

Optimizing the photovoltaic efficiency of dye-sensitized solar cells (DSSC) based on staggered gap heterojunctions requires a detailed understanding of sub-band gap transitions in the visible from the dye directly to the substrate's conduction band (CB) (type-II DSSCs). Here, we calculate the optical absorption spectra and spatial distribution of bright excitons in the visible region for a prototypical DSSC, catechol on rutile TiO${}_2$(110), as a function of coverage and deprotonation of the OH anchoring groups. This is accomplished by solving the Bethe-Salpeter equation (BSE) based on hybrid range-separated exchange and correlation functional (HSE06) density functional theory (DFT) calculations. Such a treatment is necessary to accurately describe the interfacial level alignment and the weakly bound charge transfer transitions that are the dominant absorption mechanism in type-II DSSCs. Our HSE06 BSE spectra agree semi-quantitatively with spectra measured for catechol on anatase TiO${}_2$ nanoparticles. Our results suggest deprotonation of catechol's OH anchoring groups, while being nearly isoenergetic at high coverages, shifts the onset of the absorption spectra to lower energies, with a concomitant increase in photovoltaic efficiency. Further, the most relevant bright excitons in the visible region are rather intense charge transfer transitions with the electron and hole spatially separated in both the [110] and [001] directions. Such detailed information on the absorption spectra and excitons is only accessible via periodic models of the combined dye-substrate interface.

arXiv comment9 pages, 4 figures, 3 tables

References in corpus (12)

• Van der Waals Density Functional for General Geometries
• Van der Waals density functionals applied to solids
• Efficient implementation of a van der Waals density functional: Application to double-wall carbon nanotubes
• Level alignment of a prototypical photocatalytic system: Methanol on TiO2(110)
• Quasiparticle level alignment for photocatalytic interfaces
• Trends in Metal Oxide Stability for Nanorods, Nanotubes, and Surfaces
• Comparing quasiparticle H${}_2$O level alignment on anatase and rutile TiO${}_2$
• Quasiparticle interfacial level alignment of highly hybridized frontier levels: H${}_2$O on TiO${}_2$(110)
• Coverage Dependence of the Level Alignment for Methanol on TiO${}_2$(110)
• Using $G_0{W}_0$ Level Alignment to Identify Catechol's Structure on TiO${}_2$(110)
• Photoinduced Absorption within Single-Walled Carbon Nanotube Systems
• PFO-BPy Solubilizers for SWNTs: Modelling of Polymers from Oligomers

Cited by in corpus (3)

• Conditions for electronic hybridization between transition-metal dichalcogenide monolayers and physisorbed carbon-conjugated molecules
• Optical Absorption and Energy Loss Spectroscopy of Single-Walled Carbon Nanotubes
• Tailoring a Molecule's Optical Absorbance Using Surface Plasmonics