Browsing by Subject "Electron-hole generation"
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Item Open Access Anatase TiO2 nanowires functionalized by organic sensitizers for solar cells: a screened Coulomb hybrid density functional study(American Institute of Physics Inc., 2015) Ünal, H.; Gunceler, D.; Gülseren, O.; Ellialtıoğlu, S.; Mete, E.The adsorption of two different organic molecules cyanidin glucoside (C21O11H20) and TA-St-CA on anatase (101) and (001) nanowires has been investigated using the standard and the range separated hybrid density functional theory calculations. The electronic structures and optical spectra of resulting dye-nanowire combined systems show distinct features for these types of photochromophores. The lowest unoccupied molecular orbital of the natural dye cyanidin glucoside is located below the conduction band of the semiconductor while, in the case of TA-St-CA, it resonates with the states inside the conduction band. The wide-bandgap anatase nanowires can be functionalized for solar cells through electron-hole generation and subsequent charge injection by these dye sensitizers. The intermolecular charge transfer character of Donor-π-Acceptor type dye TA-St-CA is substantially modified by its adsorption on TiO2 surfaces. Cyanidin glucoside exhibits relatively stronger anchoring on the nanowires through its hydroxyl groups. The atomic structures of dye-nanowire systems re-optimized with the inclusion of nonlinear solvation effects showed that the binding strengths of both dyes remain moderate even in ionic solutions.Item Open Access Hybrid functional calculated optical and electronic structures of thin anatase TiO2 nanowires with organic dye adsorbates(Elsevier, 2015) Ünal, H.; Gunceler, D.; Gülseren, O.; Ellialtioğlu, Ş.; Mete, E.The electronic and optical properties of thin anatase TiO2 (1 0 1) and (0 0 1) nanowires have been investigated using the screened Coulomb hybrid density functional calculations. For the bare nanowires with sub-nanometer diameters, the calculated band gaps are larger relative to the bulk values due to size effects. The role of organic light harvesting sensitizers on the absorption characteristics of the anatase nanowires has been examined using the hybrid density functional method incorporating partial exact exchange with range separation. For the lowest lying excitations, directional charge redistribution of tetrahydroquinoline (C2-1) dye shows a remarkably different profile in comparison to a simple molecule which is chosen as the coumarin skeleton. The binding modes and the adsorption energies of C2-1 dye and coumarin core on the anatase nanowires have been studied including non-linear solvation effetcs. The calculated optical and electronic properties of the nanowires with these two different types of sensitizers have been interpreted in terms of their electron-hole generation, charge carrier injection and recombination characteristics.