Tunable Band Edges of TiO2 via Functionalization with Phosphonic Acid Adsorbates

ORAL

Abstract

The deliberate design of semiconductor surfaces with band edge energies optimal for electro- or photoelectrochemical applications is a grand challenge. We examine the extent that the band edges of anatase TiO2(101) can be effectively tuned via molecular adsorption on its surface. Using density functional theory, we compute TiO2 band edge energies for a series of phosphonic acid molecules, whose intrinsic dipole moments are significantly different in both magnitude and direction. The results reveal that the molecule-substrate binding leads to a large induced dipole moment, and the induced dipole upon adsorption varies with the binding nature and configuration. Repulsive dipole-dipole interactions between molecules lead to a striking coverage-dependence of the effective dipole moments. Interestingly, computed band edge shifts in TiO2 are in excellent agreement with the experimentally measured work-function changes. Implications for the role of such adsorbates on photoelectrochemical devices will be discussed.

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Authors

  • Guo Li

    Molecular Foundry, Lawrence Berkeley National Laboratory

  • Jessy Rivest

    Molecular Foundry, Lawrence Berkeley National Laboratory

  • Ian Sharp

    Joint Center for Artificial Photosynthesis, Lawrence Berkeley National Laboratory

  • Delia Milliron

    Molecular Foundry, Lawrence Berkeley National Laboratory

  • Jeffery B. Neaton

    Department of Physics, UC-Berkeley; Molecular Foundry, LBNL, Molecular Foundry, LBNL, Department of Physics, UC Berkeley, Molecular Foundry, LBNL and Dept. Physics, UC Berkeley, Molecular Foundry, Lawrence Berkeley National Laboratory and Department of Physics, University of California, Berkeley, UC Berkeley, Dept of Physics; Materials Science Division, LBNL, Molecular Foundry, Lawrence Berkeley National Laboratory; Department of Physics, UC-Berkeley, The Molecular Foundry, LBNL; Dept. of Physics, University of California, Berkeley, Lawrence Berkeley National Laboratory, UC Berkeley Department of Physics, Lawrence Berkeley Natl Lab and Department of Physics, UC-Berkeley, Physics Department, UC Berkeley; Molecular Foundry, Lawrence Berkeley National Lab