Nitrocatechol/ZnO Interface: The Role of Dipole in a Dye/Metal-Oxide Model System

Abstract

The electronic properties of a prototype system suitable for dye-sensitized solar cell applications are investigated both experimentally and theoretically by means of electron spectroscopies (high-resolution electron energy loss spectroscopy, HREELS, and ultraviolet and X-ray photoemission spectroscopies, UPS and XPS) and first-principles density functional theory (DFT)-based calculations. The comparison of HREELS and UPS data with the DFT results allows the microscopic description of electronic structure modifications upon interface formation, and provides a quantitative evaluation of the ionization energy and electron affinity changes induced by functionalization: these variations can be associated to the electric dipole of the functional species and, thus, to the formation of an interface dipole layer

Probing environmentally significant surface radicals: Crystallographic and temperature dependent adsorption of phenol on ZnO

“…We assign this shoulder structure at the edge of the valence band maximum (3.7 BE) to be the phenol HOMO band, which primarily lies in the band gap of ZnO. This assignment is consistent with other aromatics on ZnO [28,29]. In addition, another peak emerges at approximately 14 eV that has been assigned to the phenol sigma orbitals [30].…”

“…However, when the adsorption occurs at elevated temperature (220 °C) the spectrum (Figure 2f) shifts significantly to lower loss energy by 0.7 eV compared to Figure 2b. More importantly, EELS shows the intensity feature at 2.3 eV which is presumably due to additional transitions from the HOMO of phenol to the conduction band minimum (CB min ) of ZnO similar to the nitrocatechol system studied by Arnaud et al [29]. Also, two very prominent peaks are observed at excitation energies of approximately 4.0 and 5.8 eV.…”

Synthesis of Zinc Tetraphenylporphyrin Rigid Rods with a Built-In Dipole

“…14 −19 On transition metal oxide semiconductors, the adsorption of structurally simple molecules to form polar layers was found to shift the position of the semiconductor conduction band and influence the open circuit photovoltage and other parameters in dye-sensitized solar cells. [20][21][22][23][24][25][26]11,13 As part of our interest in molecules/semiconductor interfaces, we recently demonstrated that two Zn(II) tetraphenylporphyrins having the structure porphyrin-linkeranchor with a reversible built-in dipole in the linker shift a molecule's energy levels alignment on transition-metal oxide in a predictable manner. 27 The proof-of-concept experiment, which was carried out on a ZnO (11−20) single crystal surface by UV photoemission spectroscopy (UPS), is illustrated in Figure 1b.…”

“…9H) 13. C NMR (CDCl 3 ): δ 155.50, 142.47, 131.35, 124.23, 118.77, 114.95, 104.01, 99.81, 43.31, −0.37.…”

“…6H) 13. C NMR (126 MHz, CDCl 3 ): δ 165.49, 155.98, 150.33, 150.30, 150.20, 149.77, 143.63, 142.71, 139.40, 136.87, 134.64, 134.43, 132.91, 132.26, 132.15, 132.10, 131.61, 131.06, 130.87, 129.40, 127.57, 126.59, 123.76, 121.97, 121.45, 121.32, 120.42, 119.89, 119.23, 111.35, 97.10, 94.64, 88.39, 88.00, 52.62, 42.…”