title: Energy alignment and surface dipoles of rylene dyes adsorbed to TiO2 nanoparticles.
abstract: The energy loss in dye-sensitized solar cells calculated from the energy difference between the lowest electronic transition of the dye and the obtained open-circuit voltage is often 1 eV or even more. To minimize this loss, it is important to accurately determine the energy alignment at the TiO(2)/dye/redox-mediator interface. In this study, we compared the results from electrochemistry and photoelectron spectroscopy for determining the energy alignment of three rylene dyes, two of which absorb relatively far in the red. The trends observed with the methods were different, as in the former, the energy alignment is measured relative to an external reference and includes contributions from solvent reorganization energies, while in the latter, it is measured relative to the energetics of the TiO(2) and is lacking such contributions. The influence of the dyes' dipole moments on the energetics of the TiO(2) was also measured and explained some of the differences in trends. Finally, we compared the injection efficiencies of the two red-absorbing dyes and found that the differences in injection efficiencies can be better explained using the energy alignment determined from photoelectron spectroscopy. This shows that the method for measuring the energetics of a DSC should be chosen according to what process one intends to study.
authors: Department of Physical and Analytical Chemistry, Uppsala University, Box 259, 751 05 Uppsala, Sweden.
authors: Ute B
authors: UB
authors: Cappel
authors: Stefan
authors: S
authors: Plogmaker
authors: Erik M J
authors: EM
authors: Johansson
authors: Anders
authors: A
authors: Hagfeldt
authors: Gerrit
authors: G
authors: Boschloo
authors: Håkan
authors: H
authors: Rensmo
mesh_terms: D000327:Adsorption; D000465:Algorithms; D011211:Electric Power Supplies; D004563:Electrochemistry; D005456:Fluorescent Dyes / Q000737:chemistry*; D015394:Molecular Structure; D053758:Nanoparticles / Q000737:chemistry*; D010569:Perylene / Q000737:chemistry*; D056951:Photoelectron Spectroscopy; D011789:Quantum Theory; D012993:Solar Energy; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*
chemical_list: D005456:Fluorescent Dyes; C009495:titanium dioxide; D010569:Perylene; D014025:Titanium