AVS 55th International Symposium & Exhibition | |
Energy Science and Technology Focus Topic | Thursday Sessions |
Session EN+EM+NS+P+A+T+V-ThM |
Session: | Energy: Tools and Approaches |
Presenter: | S. Rangan, Rutgers University |
Authors: | S. Rangan, Rutgers University J.P. Theisen, Rutgers University E. Bersch, Rutgers University R.A. Bartynski, Rutgers University |
Correspondent: | Click to Email |
We have used direct and inverse photoemission to measure the occupied and unoccupied electronic states of N3 dye and determine their alignment with the band edges of single crystal and nanostructured TiO2 and ZnO substrates. In dye-sensitized solar cell applications, the HOMO-LUMO gap of the dye molecule determines the useful portion of the solar spectrum, and charge transfer of photoexcited electrons to the substrate depends on the alignment of the LUMO to the substrate conduction band edge. We have compared the N3 dye properties on well characterized rutile TiO2(110) and wurtzite ZnO single crystal surfaces to adsorption on more technologically relevant TiO2 anatase nanoparticle and ZnO nanorod substrates. Samples were prepared and passivated with a pivalate layer in UHV, then sensitized ex-situ in a solution of N3 dye in acetonitrile. STM measurements show that the pivalic acid forms an ordered overlayer on the TiO2(110) surface and that the N3 dye molecules can be imaged after sensitization. For N3 on TiO2(110) as shown below, our spectroscopic measurements show that passivation significantly reduces contamination (presumably from water in the ambient) and that the N3 HOMO occurs at 0.9 eV above the TiO2 valence band edge, while the LUMO is found 0.5 eV above the conduction band edge. On ZnO , the N3 HOMO occurs at 1.3 eV above the ZnO valence band edge but the N3 LUMO occurs 2.1 eV above the conduction band edge, much higher than what is measured on TiO2. Comparison with experimental and theoretical values from the literature will be discussed.