| AVS 57th International Symposium & Exhibition | |
| Energy Frontiers Topical Conference | Wednesday Sessions |
| Session EN+NS-WeM |
| Session: | Organic Photovoltaics |
| Presenter: | S. Gutmann, University of South Florida |
| Authors: | S. Gutmann, University of South Florida M.A. Wolak, University of South Florida M.M. Beerbom, University of South Florida R. Schlaf, University of South Florida |
| Correspondent: | Click to Email |
The electronic structure of the interfaces in dye-sensitized solar cell structures was investigated using x-ray and ultraviolet photoemission spectroscopy (XPS, UPS). Electrospray thin film deposition in high vacuum was used to build the interfaces of interest directly in vacuum without exposure to the ambient. Electrospray enables the fabrication of clean, essentially uncontaminated thin films of organic molecules and nanoparticles directly in vacuum.
The experiments focused on the investigation of the indium tin oxide (ITO)/nanocrystalline TiO2 interface, as well as the characterization of the TiO2/RuL2(NCS)2 [cis-bis(4,4’-dicarboxy-2,2’-bipyridine)–bis(isothio-cyanato)-ruthenium(II)] (“N3”, a prototypical dye used in many currently pursued device structures)-dye interface. Both TiO2 and N3 films were built up in several steps. After each step, characterization by XPS and UPS was performed. The resulting sequence of spectra allowed the determination of charge injection barriers and interface dipoles at the ITO/TiO2 and TiO2/N3 interfaces. Our experiments revealed a strong influence of the UV radiation during UPS measurements on the band line-up at these interfaces. This was revealed though low intensity x-ray photoemission spectroscopy (LIXPS) measurements, which allow the measurement of the work function prior to UV exposure. These results suggest that even low-level UV radiation, such as encountered in an encapsulated solar cell, may lead to cell degradation over time due to a re-alignment of the electronic structure with detrimental effect on charge transport.