Photoemission studies of donor/acceptor materials for photovoltaic applications

The development of novel organic materials for use in organic-based photovoltaic cells has been of considerable interest due to their lower cost and ease of processing compared with traditional devices prepared from inorganic semiconductors. Photoemission spectroscopy can be applied to the characterization of these thin films due to the surface sensitivity of the technique and the ability to examine interfacial properties in a multilayer system.;Ultraviolet photoelectron spectroscopy (UPS) is used to probe the interface between polythiophene-like films grown by surface polymerization by ion-assisted deposition (SPIAD) and various substrates to examine the dependence of the energy level alignment on the substrate work function and film deposition parameters. Comparison of the valence band electronic structure obtained by UPS for 2-methoxy-5-(2'-ethylhexyloxy)-1,4-bis((4',4"-bisstyryl) benzene) (MEH-OPV5) films and phenylene vinylene films grown by SPIAD shows changes in the underlying chemical structure of the ion-modified films that lead to morphological changes. X-ray photoelectron spectroscopy (XPS) using 200 eV photon energy provides increased surface sensitivity to examine the interaction of the nanocrystal surface with the organic matrix in PbS/organic nanocomposite films and is compared to XPS obtained using 1486.6 eV photon energy. XPS is also extended to the contactless measurement of element-specific electrical ", properties of MEH-OPV5 and SPIAD films and photovoltaic properties of PbS/organic nanocomposite films by exploiting differential charging between multiple system components of varying conductivities.