TitleElectronic energy level alignment of dye molecules on TiO2 and ZnO surfaces for photovoltaic applications
NameTheisen, Jean-Patrick (author), Bartynski, Robert (chair), Feldman, Leonard (internal member), Zimmermann, Frank (internal member), Rutgers University, Graduate School - New Brunswick,
Dye-sensitized solar cells,
DescriptionIn dye-sensitized solar cells (DSSC), the attributes of the dye-semiconductor interface are of important interest. In this thesis, electronic and structural aspects of dye/semiconductor systems have been studied experimentally using ultraviolet photoemission spectroscopy (UPS), inverse photo electron spectroscopy (IPS) and scanning tunneling microscopy (STM).
In this work the electronic structure of N3, or more precisely Ru(4,4-dicarboxylate-2,2-bipyridine)2-(NCS)2, molecules absorbed on rutile TiO2(110) single crystal and anatase TiO2 nanoparticles has been studied and has shown that the energy of highest occupied molecular orbital (HOMO) of the N3 dye is located near the middle of the semiconductor band gap and that the lowest unoccupied molecular orbital (LUMO) level overlaps with the Ti 3d orbitals of the TiO2 conduction band. A shift of the UPS/IPS energy spectra indicates the formation of an induced dipole upon N3 adsorption on the TiO2 surface.
The electronic contributions of N3 in combination with ZnO are similar to N3 absorbed on TiO2. The position of the HOMO is almost identical in regard to the band edge of the valence band, but the LUMO is located a bit higher in energy in regard the conduction band minimum (CBM) as in comparison with N3/TiO2. We studied also the adsorbate isonicotinic acid (INA) with chemical structure: C6H5NO2 on the oxides, because it is a good model for the binding ligand of the N3 molecule and which is where the spatial distribution of the N3 LUMO is expected to be delocalized. Indeed, the electronic structure of the LUMO for INA adsorbate is for both semiconductors is very similar to the LUMO of the adsorbate N3 dye.
Another dye, catechol (C6H6O2), has been reported that catechol bonds strongly to TiO2 and that electrons can be excited directly from the catechol HOMO to the conduction band of TiO2. Our experiments show that the LUMO is indeed mixed significantly with the conduction band of TiO2.
A monolayer of pivalate ((CH3)3CCOO-) ions was used to protect the sample surface from contamination during the wetting process of the N3 adsorption. The effect of passivation on the quality of the semiconductor/dye interface is studied by UPS and IPS measurements.
NoteIncludes bibliographical references (p. 83-87)
Noteby Jean-Patrick Theisen
CollectionGraduate School - New Brunswick Electronic Theses and Dissertations
Organization NameRutgers, The State University of New Jersey
RightsThe author owns the copyright to this work.